Upcoming Events
Archana Kamal, Northwestern University, 5/01/2025
Title: TBA
Abstract: TBA
Time: Thursday 5/01/2025, 11:00 AM EST
Location: 726 Broadway, Room 1067
Giordano Scappucci, Delft University of Technology, 3/28/2025
Title: TBA
Abstract: TBA
Time: Friday 3/28/2025, 11:00 AM EST
Location: 726 Broadway, Room 1067
Georgios Katsaros, Institute of Science and Technology Austria, 3/13/2025
Title: TBA
Abstract: TBA
Time: Friday 3/13/2025, 11:00 AM EST
Location: 726 Broadway, Room 1067
Nathalie de Leon, Princeton University, 2/13/2025
Title: TBA
Abstract: TBA
Time: Thursday 2/13/2025, 11:00 AM EST
Location: 726 Broadway, Room 1067
Kin Chung Fong, Northeastern University, 1/30/2025
Title: TBA
Abstract: TBA
Time: Monday 1/30/2025, 11:00 AM EST
Location: 726 Broadway, Room 1067
Ludovic Perret, Laboratoire d’Informatique de Paris 6, 12/12/2024
Title: Public-Private Initiative in Post-Quantum Cryptography
Abstract: The possible construction of a large-scale quantum computer poses a systemic threat to currently deployed public-key cryptography. Shor’s quantum algorithms permit to break number-theoretic cryptosystems (such as Diffie-Hellman, RSA, ECDSA) which form the security backbone of digital communications. Post-Quantum Cryptography (PQC) is a solution to mitigate this risk and provides a new generation of cryptography designed to be resistant against any powerful quantum computer. Recently, PQC has received much attention from standardization bodies (e.g., the NIST PQC standardization processes) and policy sectors (e.g., the US Quantum Computing Cybersecurity Preparedness Act). After five years and three rounds of selection, NIST selected the first set of PQC standards in 2022. This selection is a major milestone marking a new era of (post-quantum) cryptography. NIST standardization marks the first step toward a wide-scale deployment of PQC. However, this transition from legacy networks protected with classical cryptography to a more robust, quantum-resistant, infrastructure is especially challenging. Many open questions at the intersection of fundamental research and innovation need to be addressed in the short term. This talk will present some of these challenges and a new initiative at Sorbonne University that aims to gather academics, the public sector at large, and industry to address fundamental and industrially relevant open problems. This initiative is structured around three main scientific axes, 1) basic security analysis of pos-quantum schemes, 2) tools to help the transition, and 3) design of enhanced primitives/protocols. The initiative also includes a multidisciplinary track that will consider the impact of post-quantum cryptography beyond the pure scientific/technical questions : standardization, regulation, policy issues, and innovation.
Time: Monday 12/12/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Edwin Barnes, Virginia Tech, 12/09/2024
Title: Control-based variational quantum algorithms and dynamical noise suppression
Abstract: The simulation of strongly correlated systems is one of the most exciting potential applications of quantum computers. There is hope that variational algorithms could enable the simulation of classically intractable problems on near-term devices, but this requires significant reductions in both variational circuit depths and measurement counts. I will discuss our recent efforts to lower these resource demands by eliminating quantum gates and circuits completely and instead optimizing control pulses directly. I will also describe a general approach to designing control pulses that suppress noise while implementing qubit rotations that is based on shaping geometric space curves.
Time: Monday 12/09/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Aaron Chou, Fermilab and University of Chicago, 12/05/2024
Title: A quantum computer as an axion dark matter detector
Abstract: The QCD axion model solves the longest standing problem in fundamental physics – the vanishing of the neutron electric dipole moment – while also providing a cosmological origin story for dark matter. While present axion dark matter search experiments are limited by quantum zero point noise, new single microwave photon receivers based on superconducting qubits provide orders of magnitude noise reduction below the standard quantum limit. Using advanced quantum information processing techniques currently in development, next generation experiments will be the first to deploy a rudimentary quantum computer as the front end for the readout electronics. Combined with recent advances in magnetic field-compatible microwave cavities, these experiments will finally reach sensitivity to the predicted axion-photon couplings over a decade in mass in the 10-100 micro-eV range.
Time: Monday 12/05/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Past Events
Dirk Morr, University of Illinois Chicago, 11/14/2024
Title: Topological Superconductivity, Majorana Zero Modes and Quantum Algorithms in Magnet-Superconductor Hybrid Systems
Abstract: Magnet-Superconductor Hybrid (MSH) systems have proven to be versatile platforms for the engineering of topological superconductivity and the ensuing Majorana zero modes, an important step towards the realization of topological quantum computing. In particular, the experimental ability to create MSH system with widely varying magnetic structures — from ferromagnetic and skyrmion-like to antiferromagnetic – has provided an unprecedented opportunity to manipulate and explore topological phases. In this talk, I will review some recent progress in the theoretical prediction and experimental realization of novel topological superconducting phases – ranging from strong and higher order topological superconductors to topological nodal-point superconductivity — in MSH systems. Moreover, I will demonstrate how the manipulation of the magnetic structure in MSH systems provides a new path to braiding MZMs and to the real time simulation of topologically protected quantum algorithms.
Time: Thursday 11/14/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Julian Martinez-Rincon, Brookhaven National Lab, 11/7/2024
Title: The New York State Quantum Internet Testbed (NYSQIT)
Abstract: Brookhaven National Laboratory and Stony Brook University are building a Quantum Network to distribute entanglement along the New York metropolitan area. This hybrid quantum-classical network is designed to demonstrate quantum entanglement swapping in a memory-assisted quantum repeater operation, and it will be used to explore applications in quantum communication, quantum computing, and quantum sensing. Fiber-connected and free-space links are being developed for quantum distribution of entanglement. During this talk, I will present a description of the project, its vision, and the current work to tailor atomic systems for distributed quantum processing of information.
Time: Thursday 11/7/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Mazyar Mirrahimi, INRIA Paris, 11/5/2024
Title: Cat-qubits for hardware-efficient fault-tolerant quantum computation
Abstract: Bosonic cat qubits stabilized by two-photon driven dissipation represent a promising approach towards hardware-efficient and fault-tolerant quantum computation. In this talk, I will explain the functioning of the Asymmetrically Threaded SQUID, a nonlinear dipole element, that implements the two-photon exchange Hamiltonian while avoiding harmful interactions. I will also explain how the same device can further be used to engineer the interactions required for performing protected operation of cat qubit. Finally, I will present recent experimental results where the ATS is further used to perform the Wigner tomography of the encoded states.
Time: Tuesday 11/5/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Muqing Yu, University of Pittsburgh, 10/31/2024
Title: KTaO3-based superconducting nanodevices
Abstract: The KTaO3 (KTO)-based two-dimensional electron gas (2DEG) has recently raised interest in the field of complex oxides, due to the discovery of its superconductivity that strongly depends on the KTO interface orientation. Under conductive atomic force microscope (c-AFM) lithography, metal-to-insulator transition of the KTO 2DEG can be reversibly controlled with nanoscale resolution. Using this technique, KTO-based superconducting weak links and SQUIDs are patterned and characterized. These devices reflect the underlying high kinetic inductance (~2nH/sq) and low superfluid density of the KTO 2DEG. By engineering the weak link geometry, supercurrent diodes can also be realized. The unusual inductive and capacitive properties of KTO, along with the development of nanodevices, positions KTO as a promising future platform for superconducting microwave circuits.
Time: Thursday 10/31/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
David Perconte, Institut Neel Grenoble, 10/17/2024
Title: Evidence for chiral supercurrent in quantum Hall Josephson junctions.
Abstract: We present evidence that ultra-narrow Josephson junctions defined in encapsulated graphene nanoribbons exhibit a chiral supercurrent, visible up to 8 T, and carried by the spin-degenerate QH edge channel. 2Φ0periodic oscillation of the supercurrent emerge at constant filling factor that is when the area of the loop formed by the QH edge channel is constant. By varying the junction geometry, we show that reducing the superconductor/normal interface length is pivotal to obtain a measurable supercurrent on QH plateaus, in agreement with theories predicting dephasing along the superconducting interface. Our findings mark a critical milestone along the path to explore correlated and fractional QH-based superconducting devices that should host non-Abelian Majorana and parafermion zero modes.
Time: Thursday 10/17/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Layla Hormozi, Brookhaven National Lab, 10/16/2024
Title: Minimal Quantum Circuits for Simulating Fibonacci Anyons
Abstract: The Fibonacci topological order is the prime candidate for the realization of universal topological quantum computation. Here we devise minimal quantum circuits to demonstrate the non-Abelian nature of the doubled Fibonacci topological order, as realized in the Levin-Wen string net model. We show that the fusion channels of thisi model can be detected using only three qubits, twisting phases can be measured using five, and braiding can be demonstrated using nine qubits, all with a single-qubit measurement. These designs provide the simplest possible settings for demonstrating the properties of Fibonacci anyons and can be used as realistic blueprints for implementation on many modern quantum architectures. The talk will be based on arXiv:2407.21761.
Time: Thursday 10/16/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Yuval Oreg, Weizmann Institute of Science, 10/9/2024
Title: Topological superconductivity in phase-controlled Josephson junction arra
Abstract: The search for low-dimensional topological superconductivity is fueled by the promise of new and exotic physics, such as chiral superconductivity and non-Abelian anyons. However, the need to break time-reversal symmetry, usually by applying a relatively large external magnetic field, has hindered the realization of these novel phases of matter due to the deterioration effects of the field on the superconductor. We propose to break the time-reversal symmetry by controlling and tuning the superconductors’ phases only to a regime where topological superconductivity emerges without needing an external exchange field. Our platforms rely on commonly available semiconductor-superconductor heterostructures, where spin-orbit coupling plays a central role. The main advantages of our approach over the existing ones are its tunability, suitability to a wide range of materials, and lack of magnetic field-induced impurity states. We complement simplified models by analyzing disorder effects and transport simulations.
Time: Thursday 10/9/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Eli Levenson-Falk, University of Southern California, 9/30/2024
Title: Balancing on Bloch: enhancing qubit sensitivity with coherence stabilization
Abstract: Since its invention in 1950, Ramsey interferometry has been the gold standard for measurement of a qubit’s frequency. This measurement forms the basis of many quantum sensing protocols and quantum computing gate calibrations. Unfortunately, decoherence limits the sensitivity of this frequency measurement. I will present our recent results deriving and demonstrating a protocol for unconditionally enhancing the signal-to-noise ratio of a qubit frequency measurement. Our protocol uses strictly deterministic Hamiltonian control to stabilize one component of the qubit state, preserving coherence and allowing the sensing signal to grow. We show that it is possible to improve SNR per measurement shot by up to a factor of 1.96 and SNR per evolution time by up to a factor of 1.18, and experimentally demonstrate improvement factors of 1.6 and 1.1 in a superconducting transmon qubit. The protocol requires no extra experimental resources and can be applied in a wide variety of qubit systems. I will discuss possible extensions of our results to further enhance sensitivity.
Time: Monday 9/30/2024, 2:00 PM EST
Location: 726 Broadway, Room 1067
Arunav Bordoloi, University of Maryland, 9/26/2024
Title: Flux-Tunable Qubits and Spin Cross-Correlation Experiments in Semiconducting-Superconducting Heterostructures
Abstract: Semiconducting-superconducting hybrid heterostructures provide an ideal system for investigating wide range of phenomena, for example to study qubit transitions in a gate-tunable transmon (gatemon) qubit [1] and demonstrate spin correlations in quantum mechanical systems [2]. To this end, we demonstrate the operation of split-junction gatemons biased at the half-integer flux quantum [3], which do not require any electrical gating at all. Such “gateless gatemon” qubits naturally acquire a strong anharmonicity, as large as 2400%, while remaining first-order insensitive to flux noise. The observed rich transition spectra can be explained by the interference of supercurrents carried by 2e- and 4e-charges across the junctions. Another useful property of the half-integer flux bias operation is a partial suppression of the transition matrix element responsible for the dielectric energy relaxation. The bare minimum design of gateless gatemons combined with their broad frequency tuning range provide an efficient mechanism for comparing various super-semi materials platforms and implementing novel partially-protected qubits. In addition, we have also introduced ferromagnetic split-gates (FSGs) to individually polarize the electron spins in semiconducting InAs nanowire (NW) quantum dots (QDs) [4]. We then implement such spin filters in a Cooper pair splitting (CPS) device, an electronic device that emits electrons originating from Cooper pairs, to demonstrate the direct measurement of the spin cross-correlations [2] between the currents emitted from the ‘splitting’ of spin-singlet Cooper pairs. We find a negative spin correlation of -1/3, which deviates from the ideal value mostly due to the overlap of the Zeeman split quantum dot states. Our results demonstrate a new route to perform spin correlation experiments in nano-electronic devices, especially suitable for those relying on magnetic field sensitive superconducting elements, like triplet or topologically non-trivial superconductors. [1] L. Casparis et al., Nature Nanotechnology 13, 915-919 (2018) [2] A. Bordoloi et al., Nature 612, 454-458 (2022) [3] A. Bordoloi et al., “Gateless gatemon qubit based on two-dimensional InAs/Al heterostructure”, in preparation [4] A. Bordoloi et al., Communication Physics 3, 135 (2020)
Time: Thursday 9/26/2024, 2:00 PM EST
Location: 726 Broadway, Room 1067
Wolfgang Pfaff, University of Illinois at Urbana-Champaign, 9/26/2024
Title: Generating and stabilizing entanglement in distributed quantum devices
Abstract: Mediating interactions and generating entanglement between separated qubits is a fundamental physics problem, as well as an important ingredient for scalable quantum technology. On one hand, the ability to create entanglement between qubits that are not immediate neighbors enables modular quantum devices and high connectivity in quantum processors. On the other hand, it is an intriguing fundamental question to ask what the limits are for creating pure entangled states between non-interacting qubits. I will discuss ongoing efforts in my group that are targeting both practical and fundamental aspects, using the circuit QED platform: For one, we have realized two-qubit gates with high fidelities through detachable and reconfigurable cable connections [1]; this effort is geared towards developing means to scale quantum processors beyond single wafers. Next, we are developing routing schemes that will enable all-to-all connectivity for ‘plug & play’ connected networks [2]. Finally, we have developed a driven-dissipative protocol with which we aim to show experimentally steady-state remote entanglement between qubits that do not interact coherently. This effort can be understood as a way of using bath engineering to mediate interactions [3,4]. Through these approaches we aim to advance scaling of superconducting quantum devices and shed light on the question how distributed quantum states may be preserved in open systems. [1] Mollenhauer, M., Irfan, A., Cao, X., Mandal, S. & Pfaff, W. arXiv:2407.16743 (2024). [2] Cao, X., Irfan, A., Mollenhauer, M., Singirikonda, K. & Pfaff, W. arXiv:2405.15086 (2024). [3] Lingenfelter, A. et al. Phys. Rev. X 14, 021028 (2024). [4] Irfan, A. et al. Phys. Rev. Research 6, 033212 (2024).
Time: Thursday 9/26/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Jesse E. Balgley, Columbia University, 9/19/2024
Title: Crystalline Josephson junctions for compact superconducting qubits
Abstract: State-of-the-art superconducting qubits face materials limitations that inhibit both the improvement of coherence times and the miniaturization required for scalability. Crystalline materials, with their pristine structural order and exceptional electronic properties, offer an ideal yet relatively unexplored platform to overcome these limitations. In this talk, we present DC electronic transport characterization of crystalline vertical Josephson junctions composed of the layered superconductor NbSe2 interposed with weak links of the layered semiconductor WSe2. As the thickness of the semiconducting weak link is varied, the junctions exhibit a crossover from proximity-type to tunneling-type junction behavior. Using observed trends in critical current density versus weak link thickness, we design a fully crystalline “merged-element transmon”—a novel compact qubit in which fields are confined to dielectrics and interfaces in a parallel plate structure. We demonstrate dispersive coupling between this transmon and a microwave resonator, highlighting the potential of crystalline materials for high-quality, small-form-factor superconducting quantum devices.
Time: Thursday 9/19/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Thomas Smart, Forschungszentrum Jülich, 9/17/2024
Title: Thermal Laser Epitaxy for Superconducting Quantum Devices
Abstract: Over the past twenty years, the promise of quantum computing has driven significant strides in the production of superconducting quantum devices. However, for many material systems, the production of homogeneous, single-crystalline films and devices is challenging, particularly when combined with sapphire as a substrate. Within the past five years, Thermal Laser Epitaxy (TLE) [1] has emerged as a promising candidate for the production of superconducting quantum devices owing to vast parameter space of operating pressure and substrate temperature,[2] whilst be able to deposit any solid, non-radioactive element within the periodic table.[3] The material and fabrication challenges facing current superconducting devices may be addressed via a combination of ultra-pure deposition on atomically smooth interfaces and the use of an in- situ stencil mask. Within this talk, TLE will be introduced and its various advantages over existing deposition techniques will be discussed. We will then explore how TLE is being used for the growth of superconducting devices on reconstructed sapphire,[4] with a particular focus on tantalum- based devices. Via the addition of an in-situ stencil mask, we demonstrate that high quality superconducting devices can be produced via TLE, without the need for any post-growth fabrication.[5] References: [1]: W. Braun and J. Mannhart, AIP Adv. 9, 085310 (2019) [2]: T.J. Smart et al., J. Vac. Sci. Technol. A 41, 042701 (2023) [3]: T.J. Smart et al., J. Laser Appl. 33, 022008 (2021) [4]: S. Smink et al., Adv. Mater., 36, 2312899 (2024) [5]: R. Hanna et al. (in preparation) (2024)
Time: Tuesday 9/17/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Jinkwon Kim, Cornell University, 8/08/2024
Title: Strain-Dependence of Time-Reversal Symmetry Broken Superconductivity in High-Quality Sr2RuO4 Thin Films Grown by Molecular Beam Epitaxy
Abstract: Sr2RuO4 has gained much attention with its ambiguous superconducting order parameter (SOP) and possible spin-triplet state, which led to Sr2RuO4 being considered as a possible platform for topologically protected qubit. However, recent findings strongly supporting the spin-singlet state in Sr2RuO4 have introduced confusion in understanding the SOP of Sr2RuO4. Additionally, contradictory experimental results regarding the existence of a splitting between the superconducting transition temperature (Tc) and the time-reversal symmetry breaking temperature (TTRSB) under uniaxial strain have further complicated the determination of SOP. In this context, high-quality Sr2RuO4 thin films with robust superconductivity suggest alternative experimental approaches to clarifying its unclear SOPs, along with epitaxial strain engineering.
In this work, first we grew superconducting Sr2RuO4 thin films on NdGaO3 (110) substrates (-0.3 % compressive) and SrTiO3 (100) substrates (0.9 % tensile) by molecular-beam epitaxy (MBE). Our optimized Sr2RuO4 thin films show a superconducting transition temperature as high as 2.1 K and residual resistivity ratio as 122; both are the best values ever reported. Using these high-quality thin films, we studied strain-dependent TRSB Superconductivity of Sr2RuO4 thin films by scanning superconducting quantum interference device (SQUID) microscopy. The magnetic penetration depth versus temperature λ(T) in both the compressive and tensile thin films show T2 dependence, without any anomaly or TTRSB splitting. This study provide a platform for fabricating various quantum devices such as Josephson junction and micro-patterned ring devices as well as SQUID devices, which can contribute to determining the SOP in Sr2RuO4.
Time: Thursday 8/08/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Vedangi Pathak, University of British Columbia, 7/25/2024
Title: Spontaneous time-reversal breaking in d-wave superconducting heterostructures
Abstract: In this seminar, I will present recent advancements in the study of time-reversal symmetry breaking phases in superconducting heterostructures of high-Tc cuprate superconductors. I will focus on two distinct superconducting heterostructures that exhibit d+id′ and d+is order parameters, respectively. Bilayers made of high-Tc cuprate superconductor (Bi2Sr2CaCu2O8) assembled with a twist angle close to have been recently shown to spontaneously break time reversal symmetry , consistent with theoretical predictions for emergent chiral topological phase in such twisted -wave superconductors. I will explore methods for estimating the magnitude of spontaneous chiral edge currents in the time-reversal symmetry-broken phase using a minimal microscopic model. Additionally, I will show that the magnetic fields generated by these edge currents, while small, are above the detection threshold of the state-of-the-art magnetic scanning probe microscopy. Next, I will discuss time- reversal symmetry breaking in the heterostructure of a high-Tc cuprate and a conventional s-wave superconductor, resulting in a non-topological d+is superconductor. I will share insights from our ongoing research on frustrated edge currents and spontaneous flux patterns at the edges of such superconductors. Finally, I will explore how the time-reversal symmetry breaking in these systems can be harnessed for the development of novel superconducting qubits and other device applications.
Time: Thursday 7/25/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Axel LeBlanc, CEA Grenoble Center, 7/18/2024
Title: Current phase relation engineering in Ge-based JoFETs
Abstract: Recently, parity-protected superconducting qubits have emerged as promising candidates for enhancing the lifetime of quantum states. This innovative approach leverages sin(2φ) Josephson elements dominated by charge-4e supercurrent, which is the coherent transfer of pairs of Cooper pairs. In this study, we examine a highly transparent S-Sm-S Josephson field effect transistor (JoFET) fabricated from SiGe/Ge heterostructures. Initially, we utilize a SQUID with a wide and narrow JoFET to demonstrate that the current-phase relation comprises multiple and gate-tunable harmonics corresponding to charge-2ne (with n an integer) supercurrent. Their contribution is confirmed by DC measurements under radio-frequency irradiation that exhibit integer and half-integer Shapiro steps. Second, by harnessing the superconducting diode effect in a SQUID with two similar JoFETs, we identify the regime of perfect critical current symmetry. In this configuration, Shapiro steps measurements at half flux quantum reveal a pronounced reduction in the first harmonic thereby realizing a sin(2φ) Josephson element. Third, in a double SQUID device, we conduct a direct measurement of the CPR of a symmetric SQUID and report its harmonic content gate and flux-tunability. In a finely tuned configuration, we achieve a regime where the sin(2φ) component accounts for more than 95% of the total supercurrent. This result demonstrates a new promising route for the realization of parity-protected superconducting qubits with enhanced coherence properties.
Time: Thursday 7/18/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Baris Pekerten, University at Buffalo, 7/8/2024
Title: Beyond the standard model of topological Josephson junctions: Crystalline anisotropy, finite-size and diode effects, and microwave detection
Abstract: Planar Josephson junctions provide a platform to host topological superconductivity which, through manipulating Majorana bound states (MBS), could enable fault-tolerant quantum computing. With a change in Zeeman field, a planar Josephson junction undergoes a transition from trivial to topological superconductivity, accompanied by a jump in the superconducting phase difference $\phi$. A standard model of these Josephson junctions, which can be fabricated to have a nearly perfect interfacial transparency, predicts a simple universal behavior: At a single critical value of Zeeman field, the system undergoes a topological transition with a $\pi$ phase jump and a minimum in the critical superconducting current $I_c$, while applying a controllable phase difference yields a diamond-shaped topological region as a function of $\phi$ and a Zeeman field. In contrast, even for a perfect interfacial transparency, we find a much richer and nonuniversal behavior as the width of the superconductor is varied or the Dresselhaus spin-orbit coupling is considered: The Zeeman field for the phase jump, not necessarily $\pi$, is different from the value for the minimum of the $I_c$, while there is a strong deviation from the diamond-like topological region. These Josephson junctions show a striking example of a nonreciprocal transport and superconducting diode effect. Moreover, what constitutes experimental signatures of topological superconductivity and how MBS can be detected remains strongly debated. Guided by the advances in microwave spectroscopy, we consider Al/InAs-based planar Josephson junctions embedded in an RF-SQUID to identify possible microwave signatures of topological superconductivity. Remarkably, by exploring the closing and reopening of a topological gap, we show that even in a wide planar Josephson junction with many Andreev bound states, such a topological signature is distinguishable in the resonance frequency shift of a microwave drive. Our findings provide guidance for future superconducting spintronics and an important step towards experimental detection of non-Abelian statistics and implementing scalable topological quantum computing. [1] B. Pekerten, D. S. Brandão, B. Bussiere, D. Monroe, T. Zhou, J. E. Han, J. Shabani, A. Matos-Abiague, and I. Žutić, Beyond the Standard Model of Topological Josephson Junctions: From Crystalline Anisotropy to Finite-Size and Diode Effects, Applied Physics Letters 124, 252602 (2024). [2] B. Pekerten, D. S. Brandão, B. Heiba Elfeky, T. Zhou, J. E. Han, J. Shabani, A. Matos-Abiague, and I. Žutić, Microwave Signatures of Topological Superconductivity in Planar Josephson Junctions, Accepted for publication in Phys. Rev. B (Letter)
Time: Thursday 7/8/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Jia Leo Li, Brown University, 5/23/2024
Title: Broken Symmetries and Superconducting Diode Effect in Multi-Layer Graphene
Abstract: The superconducting diode effect is defined by nonreciprocity in the critical supercurrent, which has been attributed to the presence of finite-momentum Cooper pairs. In this talk, I discuss our recent observation of superconducting diode effect under zero magnetic field in multilayer graphene heterostructures. Transport nonreciprocity in and of itself must exhibit an angular dependence with varying azimuth direction of current flow. The broken symmetries associated with the diode effect are naturally encoded into properties of this angular dependence. To unravel such information, we utilize the angle-resolved measurement to extract the conductivity tensor that describes transport properties in both the linear and nonlinear channels. By investigating the interplay between transport nonreciprocity, ferromagnetism, and superconductivity, our findings suggest that the exchange-driven instability in the momentum space plays a key role in stabilizing the zero-field superconducting diode effect.
Time: Thursday 5/23/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Joel IJ Wang, Massachusetts Institute of Technology, 5/16/2024
Title: Hybrid Superconducting Quantum Circuits with van der Waals Heterostructures.
Abstract: Van der Waals materials constitute a diverse array of layered substances, spanning semi-metals, insulators, semiconductors, ferromagnetic materials, superconductors, and topological insulators. These materials can be intricately assembled to form van der Waals heterostructures, holding significant promise for constructing key components for emerging solid-state quantum computing platforms. Conversely, superconducting circuits and circuit quantum electrodynamics (cQED) techniques offer a distinctive and potent toolkit for investigating novel quantum materials, complementing traditional quantum transport measurements. In this presentation, I will explore superconducting quantum circuits constructed using van der Waals heterostructures, which play a central role in advancing and enhancing existing quantum technologies. Moreover, I will impart insights from our recent studies concerning the kinetic inductance and pairing symmetries of 2D superconductors, such as NbSe 2 and magic-angle twisted bilayer graphene (MATBG). By utilizing superconducting circuits and cQED techniques, our research endeavors to deepen understanding and harness the potential of these materials for quantum technologies.
Time: Thursday 5/16/2024, 2:00 PM EST
Location: 726 Broadway, Room 1067
Shashank Misra, Sandia National Laboratories, 5/16/2024
Title: Atomically precise fabrication and microelectronics.
Abstract: A combination of scanning tunneling microscopy and hydrogen-templated selective chemistry has been used by several groups to precisely place individual phosphorus atoms in silicon that function as qubits, and to create the circuitry which serves to initialize, manipulate, and read out these qubits. Our work focuses instead on generalizing this capability, which we term atomic precision advanced manufacturing (APAM), to have a broader impact to microelectronics. In the first part of this talk, I will detail our progress towards using APAM to improve conventional digital transistors, and to produce novel devices which leverage quantum confinement and tunneling. Many of these examples do not rely on single atom precision, but instead leverage the record-breaking doping levels produced by the APAM process, which provides control over band engineering that is reminiscent of, but distinct from, semiconductor alloying. In the second part of this talk, I will show how we have directly integrated APAM into Sandia’s complementary metal oxide semiconductor (CMOS) manufacturing process. This proof of principle opens the door to a future where APAM can enhance CMOS microsystems. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. Shashank Misra is a Distinguished Member of Technical Staff at Sandia National Laboratories. He earned a doctorate in physics from the University of Illinois at Urbana-Champaign in 2005, and since 2013, has been a member of the research staff at Sandia National Laboratories. His research interests revolve around atomic precision fabrication, the material science of MOS spin qubits, and using stochastic devices to perform neuro-inspired computation.
Time: Thursday 5/16/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Lijing Jin, Institute for Quantum Computing, Beijing, China, 5/2/2024
Title: Using the inductive-energy participation ratio to characterize a superconducting quantum chip.
Abstract: In this talk, I will introduce an inductive energy participation ratio (IEPR) method [1] for characterizing superconducting quantum chips. The method efficiently extracts the key linear and nonlinear characteristic parameters, as well as the Hamiltonian of a quantum chip layout. In theory, the IEPR provides insights into the relationship between energy distribution and representation transformation. We demonstrate the approach to solving different types of characteristic parameters in both bare and normal modes. Building upon the IEPR method, we further provide an operational procedure guiding the acquirement of the key characteristic parameters and the Hamiltonian extracted only from the quantum chip layout. This methodology empowers us to efficiently model the quantum chip layout’s Hamiltonian, offering researchers the means to assess and optimize quantum chip designs before entering the fabrication stage. It holds the promise of significant enhancements in simulation and verification techniques and represents a pivotal step towards quantum electronic design automation.
Time: Thursday 5/2/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Berk Diler Kovos, Quantum Machines, 4/29/2024
Title: Unlocking the potential of quantum-classical processing.
Abstract: In recent years, it has become increasingly clear that realizing the potential of quantum technologies require tight quantum-classical integration to overcome shortcomings of quantum systems. We will start by explaining the framework, benchmark, and metrics we, as Quantum Machines, think about regarding quantum-classical integration. We then will provide some examples from various qubit platforms on sensing, communication, and computation on the benefits of such a tight quantum-classical integration, enabled by Quantum Machines. We will then conclude with discussing the newest developments at Quantum Machines, including the OPX1000 platform, Photonic Control Unit built in collaboration with QuEra Computing and DGX-Quantum built in collaboration with Nvidia. The attendees will hear about the state-of-the-art developments in quantum technologies and will learn how Quantum Machines is powering this acceleration.
Time: Monday 4/29/2024, 10:00 AM EST
Location: 726 Broadway, Room 1067
Satyavolu Papa Rao, NY CREATES, 4/19/2024
Title: Opportunities and Challenges for Scalable Fabrication of Quantum Circuits.
Abstract: This talk will present progress made by NY CREATES and partners in developing fabrication technologies for superconducting devices utilizing state-of-the-art 300 mm wafer process tools at Albany, NY. The development of alpha-tantalum based devices including Josephson junctions, resonators, damascene capacitors, will be discussed. The fabrication of superconducting TaN, NbN nanowires for applications in lumped element resonators and SNSPDs will be presented, along with initial results on establishing process flows for Al-based Josephson junctions. Ongoing work to establish a Design Rule Manual, and a Process Design Kit for the fabrication of superconducting quantum circuits will be described. The talk will conclude with a discussion of the challenges by the community in scaling quantum computing, and how new approaches might allow us to break free of prior constraints. The work done by the NY CREATES team has been in close collaboration with AFRL, Seeqc, BNL, PNNL, Auburn and Syracuse, with funding from AFRL, DOE and from NYS.
Time: Thursday 4/19/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Eliot Kapit, Colorado School of Mines, 4/18/2024
Title: On the approximability of random-hypergraph MAX-3-XORSAT problems with quantum algorithms
Abstract: Constraint satisfaction problems are an important area of computer science. Many of these problems are in the complexity class NP which is exponentially hard for all known methods, both for worst cases and often typical. Fundamentally, the lack of any guided local minimum escape method ensures the hardness of both exact and approximate optimization classically, but the intuitive mechanism for approximation hardness in quantum algorithms based on Hamiltonian time evolution is poorly understood. We explore this question using the prototypically hard MAX-3-XORSAT problem class. We conclude that the mechanisms for quantum exact and approximation hardness are fundamentally distinct. We qualitatively identify why traditional methods such as quantum adiabatic optimization are not good approximation algorithms. We propose a new spectral folding optimization method that does not suffer from these issues and study it analytically and numerically. We consider random rank-3 hypergraphs including extremal planted solution instances, where the ground state satisfies an anomalously high fraction of constraints compared to truly random problems. We show that, if we define the energy to be E=Nunsat−Nsat, then spectrally folded quantum optimization will return states with energy E≤AEGS (where EGS is the ground state energy) in polynomial time, where conservatively, A≃0.6. We thoroughly benchmark variations of spectrally folded quantum optimization for random classically approximation-hard (planted solution) instances in simulation, and find performance consistent with this prediction. We do not claim that this approximation guarantee holds for all possible hypergraphs, though our algorithm’s mechanism can likely generalize widely. These results suggest that quantum computers are more powerful for approximate optimization than had been previously assumed.
Time: Thursday 4/18/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Srivatsan Chakram, Rutgers University, 4/04/2024
Title: Error-Resilient Control and Logical Operations in Low-Loss Multimode Bosonic Circuit QED Systems
Abstract: Superconducting circuits have emerged as a promising platform for quantum computation, thanks to rapid advances in coherence and control over the past few decades. Most superconducting processors and simulators are based on lattices of coupled transmon circuits and rely on nearest-neighbor interactions for gate operations and entanglement. In this talk, I will describe advances in an alternative superconducting quantum computing architecture that utilizes multiple harmonic modes of a multimode cavity, all coupled to and controlled by one or a few superconducting quantum circuits. This multimode circuit-QED system capitalizes on the long coherence times of superconducting microwave cavities, which can exceed those of typical superconducting qubits by several orders of magnitude. The architecture also ensures high connectivity and hardware efficiency, enabling gate operations between any two cavity modes with only a few control lines. I will present protocols for the universal control of the multimode cavity system and for engineering novel interactions between photons. Furthermore, I will discuss new processor designs and control schemes for multimode-cavity-based processors that mitigate errors resulting from inter-mode crosstalk and faults in the ancillary circuit. Lastly, I will outline recent progress in implementing and manipulating bosonic logical qubits encoded in the cavity modes and our strategy for scaling up the size of such processors.
Time: Thursday 4/04/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Madisen Holbrook, Columbia University, 3/28/2024
Title: Atomic Defects in Stacked Two Dimensional Semiconductors
Abstract: Within the expanding family of two dimensional (2D) materials, transition metal dichalcogenides (TMDs) have been established as attractive candidates for semiconductors in future 2D devices. Semiconductor electronic properties are strongly modified by defects, which can be detrimental to device performance, or beneficial as a tool to engineer electronic properties. Following the example of silicon, future 2D device performance hinges on achieving high-purity TMDs and controllably introducing known defects to harness their properties. Recent advances in 2D heterostructure device performance rely on stacking mechanically exfoliated bulk TMDs; therefore, nanoscale characterization and quantification of their native defects is of key importance. In this talk, I will present our scanning tunneling microscopy (STM) characterization of the point defects in exfoliated high-purity self-flux grown TMD monolayers, as well as bulk single crystals. I will further describe how we utilize substitutional doping of our high-purity TMDs to directly correlate STM images with the atomic lattice. I will also discuss our comparison of the defects in self-flux and chemical vapor deposition (CVT) grown TMDs, and how they modify their optoelectronic properties. Finally, I will describe our work that shows conductive atomic force microscopy (CAFM) as a reliable tool for defect quantification and characterization by direct comparison with STM.
Time: Thursday 3/28/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Andrew Higginbotham, University of Chicago, 3/26/2024
Title: Thermally enhanced superconductivity and photonic friction in Josephson junction arrays
Abstract: I will present two studies exploring the limits of superconductivity in long Josephson junction arrays. The first study shows that apparent superconductivity persists for vastly weaker chains than expected within a zero-temperature theory. This behavior is consistent with thermal effects, which effectively melt the insulator and restore superconducting behavior [1]. The second study discovers a source of dissipation arising from photon-photon interactions — photonic friction. I will discuss the possible relevance of this effect as a limitation on quality factor.
Time: Tuesday 3/26/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Mattias Fitzpatrick, Dartmouth College, 3/21/2024
Title: Quantum Simulation with Superconducting Circuits: Synthetic Quantum Matter to Non-Hermitian Sensing
Abstract: In recent years, superconducting circuits have garnered much attention due to their use in quantum computers and quantum annealers. However, this technological platform can also be used to study problems in condensed matter and many-body physics where microwave photons are the particles of interest and interactions are engineered using superconducting qubits or other nonlinearities. In this talk, I will describe my work building hyperbolic superconducting circuit lattices and the associated flat bands that arise in their band structure. From here, I will discuss recent work in my new lab at Dartmouth, where we have developed a means of controlling the effective photon hopping in lattices. Using directional amplification and phase shifters, I will show how to create effectively tunable hopping rates in the Hermitian and non-Hermitian domains. Finally, I will discuss nonlinearities in the gain-dominated regime and their implications for self-oscillation sensors.
Time: Thursday 3/21/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Abhay Narayan Pasupathy, Columbia University, 3/14/2024
Title: Teaching an old dog some new tricks.
Abstract: For several decades now, traditional solid state physics has been focused on understanding the quantum ground state properties of interesting new materials like superconductors or magnets. Experimentalists use simple techniques like measuring the resistance of a sample, and use this data to draw conclusions on the underlying physics of materials. In more recent times, dramatic advances in lasers have opened up new fields of quantum information science and dynamical control of solids. In this talk, I will discuss two meeting points between the old and the new ways of doing solid state physics based on new experiments in my laboratory. In the first, I will describe quantum sensing experiments that can detect critical behaviour near a magnetic phase transition in an atomically-thin sample. In the second, I will describe how near-field enhancement can be used to generate enormous electric fields that can dramatically tune the electronic properties of a two-dimensional semiconductor.
Time: Thursday 3/14/2024, 4:00 PM EST
Location: 726 Broadway, Room 940
Benjamin Lienhard, Princeton University, 3/14/2024
Title: Comprehensive overview of the various career trajectories of physics degree holders.
Abstract: Individuals with degrees in physics possess valuable skills that make them highly sought after in both the private and public sectors. Despite this, many students and early career scientists may not be fully aware of the diverse range of career paths available to them. In this presentation, I aim to offer a comprehensive overview of the various career trajectories of physics degree holders. By providing examples of common career paths and showcasing helpful resources for exploring different options, I intend to assist attendees in their job search and application processes. Additionally, I will share insights from my career journey, specifically focusing on the unique trajectories within the field of quantum information sciences.
Time: Thursday 3/14/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Leandro Tosi, SPEC-CEA University of Saclay, 3/11/2024
Title: Anisotropic magnetic field dependence in hybrid superconductor/semiconductor microwave resonator as a signature of unconventional induced superconductivity.
Abstract: — Simon Feyrer1 , Ignacio Lobato1 , Michael Prager1 , Dominique Bougeard1 , Carlos Balseiro2 , Marco Aprili3 , Christoph Strunk1 , and Leandro Tosi1,2 — 1 Institute of Experimental and Applied Physics, University of Regensburg, Germany — 2Centro Atomico Bariloche, Comision Nacional de Energia Atomica, Argentina — 3 Laboratoire de Physique des Solides, Université Paris-Saclay, France In this talk we will present measurements of the frequency response of a lumped element microwave resonator made out of hybrid Al/InAs super conductor/semiconductor 2D heterostructures. In our device, the inductor is a narrow wire taylored in the material, dominating the kinetic inductance contribution. The resonance frequency depends on temperature, on power and strongly on in-plane magnetic field. We have observed an anisotropic magnetic field dependence, stronger when the in-plane field is orientated perpendicular to the wire. This anisotropy can be explained by considering the contribution of the kinetic inductance of the InAs 2DEG, where the induced superconductivity is affected by the spin-orbit coupling [1]. [1] D. Phan et al., Phys. Rev. Lett. 128, 107701 (2022)
Time: Monday 3/11/2024, 10:00 AM EST
Location: 726 Broadway, Room 1067
Ahmet Oral, Middle East Technical University 3/8/2024
Title: Tip based high performance magnetic imaging using Scanning Probe Microscope (SPM) Low Temperature Confocal Raman Microscope & NV Centre Microscope.
Abstract: We will give an overview of the state of the art Scanning Probe Microscopes (SPM) for magnetic imaging in the 20mK to 300K temperature range. Recent developments in cryofree cryostats and dilution refrigerators (DR) have opened a new avenue for scientists suffering from heavy Helium costs. We shall first describe the design of High Resolution MFM which can achieve 10nm magnetic resolution. Such high resolution is possible with unprecedented ~12fm/√Hz noise floor of the cantilever deflection electronics. We have also designed a Fabry-Perot interferometer for our mK-AFM which has a measured ~1fm/√Hz noise level @ 4K as shown in Fig.1.(a), while the shot noise limit was ~0.2fm/√Hz. The system uses a dielectric multilayer coating at the end of the fiber to achieve this unprecedented noise level. We tested the microscope in MFM mode with a harddisk sample and imaging Abrikosov vortices in BSCCO as shown in Fig.1.(b)-(c). We hope to improve the noise levels further and achieve better than 5-6nm resolution for mK- MFM. We shall also describe a mK-Scanning Probe Microscopes (mK-SPM) operating in Scanning Tunnelling Microscope (STM), Scanning Hall Probe Microscope (SHPM) and Atomic/Magnetic Force Microscope (AFM/MFM) mode in a wide temperature range of 20mK-300K. mK-SHPM images of magnetic materials at 20mK will be presented. We shall also discuss our recent Low Temperature Confocal Raman Microscope results (Fig. 2) & the development of Low Temperature NV Centre Microscope using our 0.82NA/1mmWD LT-APO Objectives in our ultra-low vibration 1.5K 14T Closed Cycle Cryostats.
Time: Friday 3/8/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Ramon Aguado, Instituto de Ciencia de Materiales de Madrid, 2/29/2024
Title: From Majorana to Andreev and back.
Abstract: Subgap Andreev bound states (ABS)s near zero energy are ubiquitous in semiconductor-superconductor hybrid devices due to various physical mechanisms, making unambiguous Majorana detection extremely difficult. Interestingly, this Majorana versus Andreev controversy [1] has helped us to understand that, far from being a disadvantage, the presence of ABSs can be used to design new qubit concepts. One promising route is to encode a qubit in the spin of a quasiparticle occupying an ABS in a quantum dot-based Josephson junction [2,3]. Embedding such superconducting spin qubit in a superconducting transmon circuit, allows an intrinsic spin-supercurrent coupling providing an optimal interface with circuit quantum electrodynamics for coherent control, readout and strong coherent qubit–qubit coupling [4]. By extending this idea to four quantum dots one could demonstrate a minimal Majorana-Transmon qubit based on non-local fermion parity [5].
[1] From Andreev to Majorana bound states in hybrid superconductor-semiconductor nanowires, Elsa Prada, Pablo San-Jose, Michiel WA de Moor, Attila Geresdi, Eduardo JH Lee, Jelena Klinovaja, Daniel Loss, Jesper Nygård, Ramón Aguado, Leo P Kouwenhoven, Nature Review Physics,2, 575–594 (2020).
pagespages575–594 (2020)
[2] Singlet-Doublet Transitions of a Quantum Dot Josephson Junction Detected in a Transmon Circuit, Arno Bargerbos, Marta Pita-Vidal, Rok Žitko, Jesús Ávila, Lukas J. Splitthoff, Lukas Grünhaupt, Jaap J. Wesdorp, Christian K. Andersen, Yu Liu, Leo P. Kouwenhoven, Ramón Aguado, Angela Kou, and Bernard van Heck, PRX Quantum 3, 030311 (2022).
[3] Spectroscopy of Spin-Split Andreev Levels in a Quantum Dot with Superconducting Leads, Arno Bargerbos, Marta Pita-Vidal, Rok Žitko, Lukas J. Splitthoff, Lukas Grünhaupt, Jaap J. Wesdorp, Yu Liu, Leo P. Kouwenhoven, Ramón Aguado, Christian Kraglund Andersen, Angela Kou, and Bernard van Heck, Phys. Rev. Lett. 131, 097001 (2023)
[4] Direct manipulation of a superconducting spin qubit strongly coupled to a transmon qubit, Marta Pita-Vidal, Arno Bargerbos, Rok Žitko, Lukas J Splitthoff, Lukas Grünhaupt, Jaap J Wesdorp, Yu Liu, Leo P Kouwenhoven, Ramón Aguado, Bernard van Heck, Angela Kou, Christian Kraglund Andersen, Nature Physics, 19, 1110 (2023)
[5] Minimal Kitaev-transmon qubit based on double quantum dots, D Michel Pino, Rubén Seoane Souto, Ramón Aguado, arXiv:2309.12313 (Phys. Rev. B in press).
Time: Thursday 2/29/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Gerrit Behner, Forschungszentrum Jülich, 2/22/2024
Title: Transport studies on selectively grown topological insulator multiterminal junctions.
Abstract: The combination of an ordinary s-type superconductor with three-dimensional topological insu- lators creates a promising platform for fault tolerant topological quantum computing circuits based on Majorana braiding. The backbone of the braiding mechanism are three-terminal Josephson junc- tions. It is crucial to understand the transport in these devices for further use in quantum computing applications. Generally, hybrid devices with multiple connections leads to rich physics in terms of transport properties. First, measurements on non-superconducting multi-terminal devices will be presented where a novel trapping effect is discussed that periodically modifies the conductance in the samples. Furthermore, we present low-temperature measurements of three-terminal Bi0.8Sb1.2Te3 Josephson junctions, fabricated based on a combination of selective area growth and shadow mask evaporation. The transport properties of the junction a mapped out as a function of bias current and magnetic field. The bias current maps reveal multiple interesting transport phenomena, i.e. multiple Andreev reflections suggesting the successful fabrication of a fully coupled three-terminal junction. The junctions seem to be in good agreement with a resistively and capacitively shunted junction model, but also reveal the influence of intrinsic asymmetries and their effect on the transport in the junctions.
Time: Thursday 2/22/2024, 2:00 PM EST
Location: 726 Broadway, Room 1067 and Zoom
Benedikt Frohn, Forschungszentrum Jülich, 2/22/2024
Title: Transport spectroscopy on (Bi,Sb)2Te3 nanoribbons proximitized by aluminum as parent superconductor
Abstract: One-dimensional topological insulator nanowires which are proximitized by an s-wave superconductor and are exposed to an in-plane field are predicted to become topological superconductors [1, 2]. So far, reaching a strong proximity effect in such structures has remained an experimental challenge. In this talk, I present transport spectroscopy results on (Bi,Sb)2Te3 nanowires with Al as parent superconductor. All materials are grown via molecular beam epitaxy in a single growth run consisting of five subsequent deposition steps. To prevent diffusion of Al into (Bi,Sb)2Te3 and creating a transparent interface, we employ a thin diffusion barrier made from Pt. These devices are fabricated using stencil lithography [3] and possess contacts with varying barrier strength made of AlOx. This enables us to study the density of states and therefore to search for topological features within the induced superconducting gap, of which we measure the dependencies of different magnetic field directions as well as temperature.
Time: Thursday 2/22/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067 and Zoom
Andrei Bernevig, Princeton University, 2/15/2024
Title: Exotic Phases in Moire Systems
Abstract: I will review the experimental discoveries and amazing puzzles in Twisted Bilayer Graphene and in twisted MoTe2 which culminated with the discovery of long-thought phases of matter such as the Fractional Chern Insulator. We will then show that, theoretically, most of the puzzling properties of TBG can be explained by an exact analytic mapping of the problem to a topological heavy fermion system. This mapping links two seemingly completely different fields but, in retrospect represents a natural way of explaining all the experimental puzzles. In The MoTe2, we will show how the FCI states discovered are more complicated than initially thought, and how a correct description of the intricate nature of the system necessarily involves band mixing, which exponentially increases the difficulty of the problem.
Time: Thursday 2/15/2024, 4:00 PM EST
Location: 726 Broadway, Room 1067
Katharina Laubscher, University of Maryland, 2/15/2024
Title: Majorana zero modes in germanium-based devices.
Abstract: In this talk, I discuss the theoretical prospects for the realization of Majorana zero modes in Ge-based devices. In the main part of the talk, I focus on proximitized gate-defined one- dimensional channels in planar Ge hole gases. First, I present theoretical topological phase diagrams for different channel geometries as well as estimates for the size of the topological gap in dependence on various system parameters such as channel width, strain, and the applied out-of-plane electric field. Based on these estimates, I will critically discuss under which conditions Ge hole channels may manifest Majorana zero modes. Next, by numerically calculating the local tunneling conductance spectra in the topological phase for realistic disorder strengths, I show that the extremely high quality of current state-of-the-art Ge hole gases can be expected to lead to a significant reduction of spurious signals stemming from disorder-induced in-gap Andreev bound states, and, therefore, to less ambiguity in the experimental transport data compared to what is reported in InAs- or InSb- based platforms. Finally, if time permits, I will additionally discuss planar Josephson junctions based on two-dimensional Ge hole gases as an alternative platform for Ge-based Majorana zero modes.
Time: Thursday 2/15/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Tina Brower-Thomas, Howard University, 2/08/2024
Title: How an Interest in π-systems Led to a Career in Quantum and Quantum in three Dimensions
Abstract: Self-assembled conjugated π-systems, such as aromatic thiols, on gold substrates buoyed the field of molecular electronics and offered a unique solution to some of the challenges faced by the semiconductor industry. Another π-system that holds even a greater promise is graphene, a single atom thick layer of carbon atoms. In fact, the impact of the successful exfoliation of graphene from bulk graphite has left an indelible mark on several fields, including condensed matter physics, chemistry, and materials science. Although graphene possesses some promising properties, such as high mobility and high thermal conductivity, graphene’s lack of a bandgap and magnetic properties has impeded its use in a variety of industrial applications, including electronics and spintronics. My group aims to functionalize graphene, improving graphene’s function without fundamentally affecting its desirable properties. Although theoretical reports of graphene’s interaction with transition metal (TM) and alkali ions (AI) show a retention of graphene’s properties upon the adsorption of these atoms, experimental approaches are needed to substantiate these theoretical works. Motivated by a lack of comprehensive experimental work in this field, we have been investigating the interaction of TM and AI with the surface of graphene using chemical and electrochemical reactions. Finally, I am setting up a microwave plasma chemical vapor deposition system that will be coupled to x-ray diffraction at the Brookhaven National Laboratory Synchrotron Source for in-situ x-ray growth studies of diamond growth. In addition to discussing our work in the field, we will also discuss our contributions in quantum education and work force development.
Time: Thursday 2/08/2024, 11:00 AM EST
Location: 726 Broadway, Room 1067
Kungang Li, University of Maryland, 12/18/2023
Title: Energy relaxation time fluctuations in transmon qubits with different superconducting gaps
Abstract: Superconducting qubits are an ideal platform for quantum computing and the relaxation time T1 has increased in recent years. We have repeatedly measured the behavior of Al/AlOx/Al transmons that have electrodes with different superconducting gaps in a 3-D cavity and observed significant fluctuations. In our devices, base electrode was formed from nominally pure aluminium while the counter electrode was formed from oxygen-doped aluminium. The measurement of T1 varied from 100 to 300 μs under low temperature and the maximum T1 of the transmon observed was 310 μs at 20 mK. A device with a thin doped-Al base electrode and thick pure Al counter electrode showed T1fluctuations of a similar size with maximum T1 values over 200 μs. Measurements of the fluctuations versus temperature reveal that the standard deviation of T1 is proportional to T1. I proposed a mechanism for exploring the T1 fluctuation data and discuss the possible underlying cause of the T1 fluctuations.
Time: Monday 12/18/2023, 10:00 AM EST
Location: 726 Broadway, Room 1067
Guo-Yi Zhu, University of Cologne, 12/07/2023
Title: Nishimori’s cat in a noisy quantum processor
Abstract: Traditionally, measurements have been synonymous with extracting information from physical systems. Yet in quantum mechanics, measurements exhibit a Janus-faced character allowing them to also actively modify and steer quantum states, which forges a new route to entanglement generation and a pathway to preparing unconventional quantum states. From a conceptual point of view, it has remained an open question whether these measurement-based state preparation protocols can lead to phases of matter which are stable to gate imperfections. In this talk I will focus on a shallow circuit targeting at the “hydrogen atom” of long-range entangled states – the Greenberger-Horne-Zeilinger “cat state”. Analytically, we find that its long-range order is stable against certain coherent and incoherent errors, up to a finite threshold. The threshold is governed by Nishimori physics featuring a conspiracy (fueled by Born’s rule) of disorder and effective temperature. Experimentally, I’ll discuss an implementation of this protocol and a realization of the Nishimori transition on one of IBM’s 127-qubit quantum processor. If time permits, I’ll briefly show a generalization of this physics to non-commuting measurements and the Floquet honeycomb code, where the frustration of measurements leads to highly entangled quantum liquid.
Time: Thursday 12/07/2023, 11:00 AM EST
Location: 726 Broadway, Room 1067
Chris Palmstrøm, University of California, Santa Barbara, 11/16/2023
Title: Superconductor/Semiconductor Heterostructures for Quantum Computing Applications.
Abstract: Superconductor/semiconductor heterostructures have theoretically been predicted to have unique applications in quantum information systems. Coupling superconductivity to near surface quantum wells (QW) and nanowires of high spin-orbit semiconductors have allowed the observation of zero bias peaks, which can be a signature of, but not proof of, Majorana Zero Modes, a key ingredient for topological quantum computing. Although the Majorana Zero Modes have not been experimentally confirmed, induced superconductivity is observed and paves the way for lithographically defined complex superconductor/semiconductor nanostructured networks necessary for quantum computing. Our efforts have focused on developing high mobility of near surface quantum wells of the high spin-orbit semiconductors InAs, InSb and InAsySb1-y. Rather than just relying on post growth lithography and top down etching to form semiconductor nanostructures, we have also investigated the development of shadow superconductor growth on atomic hydrogen cleaned MOVPE-grown vapor-liquid-solid InSb nanostructures and in-vacuum chemical and molecular beam epitaxy selective area grown InAs nanostructures. We have identified Sn as an alternative for Al for use as superconductor contacts to InSb vapor-liquid-solid nanowires, demonstrating a hard superconducting gap, with superconductivity persisting in magnetic field up to 4 Tesla. Further, a small island of Sn-InSb exhibits the two-electron charging effect, a clear indication of a supercurrent. Lateral superconductor/semiconductor/superconductor structures allow for selective control of conductance modes in planar lateral multi-terminal Josephson Junctions. Vertical superconductor/semiconductor/superconductor heterostructures have the potential for combining the capacitor and Josephson Junction in a superconducting transmon qubit device into a single device, a merged element transmon, resulting in orders of magnitude reduction in size. In this presentation, my group’s progress in developing superconductor/semiconductor heterostructures for quantum computing applications will be presented. This will include progress in in-situ patterning and selective area growth, multi-terminal Josephson Junctions and the recent progress towards developing a Si fin based merged element transmon – the FinMET.
Time: Thursday 11/16/2023, 11:00 AM EST
Location: 726 Broadway, Room 1067
Katja Nowack, Cornell University, 10/19/2023
Title: Understanding electronic transport through local magnetic measurements.
Abstract: Electric charge can flow in unexpected ways through a sample, in particular in dissipationless conductors. In this talk, I will discuss how we use a local magnetic probe to visualize electronic transport in two different types of dissipationless conductors. First, we study microstructures fabricated from a heavy-fermion superconductor that exhibit an unusual resistive superconducting transition. We show that this behavior is explained by a spatially modulated transition temperature, and we discover that local strain is the cause of the spatial modulation. Second, we visualize how a non-equilibrium current flows in a quantum anomalous Hall insulator by imaging the magnetic field produced by the current. Against the prevalent expectation that the transport current is concentrated along the edges, we find that the current can flow in the interior of the sample within the dissipationless regime.
Time: Thursday 10/19/2023, 11:00 AM EST
Location: 726 Broadway, Room 1067
Kaveh Delfanazari, University of Glasgow, 10/12/2023
Title: High-yield addressable hybrid superconducting-semiconducting quantum integrated circuits
Abstract: In this talk, I will present our latest progress in the development of quantum integrated circuits based on hybrid superconductor-semiconductor two-dimensional electron gas in InGaAs heterostructure. In particular, the design, nanofabrication, and cryogenic measurements of large-scale hybrid superconductor-semiconductor field-effect conductance switches with novel chip architectures will be discussed with a focus on their electronic response, switching (on/off) statistics, quantum yield, and reproducibility [1]. If time allows, in the second part of my talk, I will discuss our recent results on the fabrication and characterisation of high-Qi factor (above million) superconducting microwave coplanar waveguide resonator arrays based on NbN, and their microwave spectroscopy from high power to single photon regime at millikelvin temperatures and high magnetic fields [2] for their integrations with hybrid quantum circuits. [1] K Delfanazari et al., arXiv:2307.04355 [2] P. Foshat et al., arXiv:2306.02356
Time: Thursday 10/12/2023, 11:00 AM EST
Location: 726 Broadway, Room 1067
Akira Oiwa, Osaka University, 10/06/2023
Title: Semiconductor spin qubits for quantum networking.
Abstract:Semiconductor spin qubit is well recognized as a promising platform for scalable fault-tolerant quantum computers (FTQCs) because of relatively long spin coherence time in solid state devices and high-electrical tuneability of the quantum states [1]. Indeed, the single qubit and two-qubit gate operation with high fidelity exceeding fault-tolerance threshold have been demonstrated [2,3,4]. These achievements have ignited research for scaling up the qubits towards million qubit systems operating based on quantum error correction. The strategy for scaling-up to million qubits is not simply arranging qubits in neighbor to each other, but building quantum networks by intermediate quantum state transfer or optical networking are considered as more effective routes to develop FTQCs. In this talk, we show two topics: the photon-polarization to spin quantum interface for connecting quantum computers to the optical quantum networks [5,6] and the other is the acceleration of the adiabatic spin state transfer bringing a concept to shortcut to adiabaticity into the intermediate spin state transfer for middle range spin quantum link [7]. [1] G. Burkard et al., Rev. Mod. Phys. 95, 025003 (2023). [2] J. Yoneda et al., Nature Nanotechology 13, 102 (2018). [3] A. Noiri et al., Nature 601, 338 (2022). [4] X. Xue et al., Nature 601, 343 (2022). [5] T. Fujita et al., Nature commun. 10, 2991 (2019). [6] K. Kuroyama et al., Phys. Rev. B 10, 2991 (2019). [7] X.-F. Liu et al., submitted.
Time: Friday 10/06/2023, 11:00 AM EST
Location: 726 Broadway, Room 1067
Daniel Loss, University of Basel, 10/05/2023
Title: Spin Qubits in Semiconductors for Scalable Quantum Computers.
Abstract:Semiconductor spin qubits offer a unique opportunity for scalable quantum computation by leveraging classical transistor technology. This has triggered a worldwide effort to develop spin qubits, in particular, in Si and Ge based quantum dots, both for electrons and for holes. Due to strong spin orbit interaction, hole spin qubits benefit from ultrafast all-electrical qubit control and sweet spots to counteract charge and nuclear spin noise . In this talk I will present an overview of the state-of-the art in the field and focus, in particular, on recent developments on hole spin physics in Ge and Si nanowires, Si FinFETs, and Ge heterostructures.
Time: Thursday 10/05/2023, 4:00 PM to 5:30 PM EST
Location: 726 Broadway, Room 940
Leo Kouwenhoven, Delft, 10/05/2023
Title: Andreev and Majorana bound states in nanoscale devices.
Abstract:Over the past decade we have studied Majorana bound states in hybrid devices of superconducting and semiconducting materials. Due to finite-size effects, unavoidable residual disorder and inhomogeneities in our devices, Majorana bound states with topological protection have not been observed. Instead of these studies in long hybrid nanowires, we have adopted a new bottom-up approach by building a Kitaev chain starting from a minimal cell. The minimal cell consists of two spin-polarized quantum dots coupled via a short, grounded superconductor. This coupling provides both single-electron tunneling between the quantum dots as well as a Cooperpair coupling via crossed Andreev reflection. We discuss how sweet spots can be found where Majorana states arise on the dots. This minimal cell is too short to develop a topological gap such that these Majorana states are only partially protection, hence these states have been dubbed ‘poor man’s Majoranas’. Relevant reference: Dvir, Wang…, Kouwenhoven, Realization of a minimal Kitaev chain in coupled quantum dots. Nature 614(7948), 445–450 (2023).
Time: Thursday 10/05/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Jason Orcutt, IBM Quantum, 09/28/2023
Title: Extending superconducting qubit systems with microwave-optical transduction
Abstract: As superconducting qubits scale to larger and more powerful computational systems, researchers are looking for new ways to interconnect them. A long sought objective is to interconnect superconducting quantum systems with optical photons to enable long distance and ambient media connections. The fundamental challenge is known as microwave-optical transduction, where the quantum information must be converted between the microwave and optical domains with high efficiency and low added noise. In this talk, I will review the current approaches being pursued in the community and at IBM Quantum to achieve this task. At the system level, I will share an introduction motivation for when these interconnects will be critically needed for scaling. At the physical level, I will discuss different material systems under consideration to build transducers and connect them to qubits. I will end with a discussion of the protocols are under development to use these transducers to extend a quantum computational system.
Time: Thursday 09/28/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Martin Weides, University of Glasgow, 09/22/2023
Title: Improved Method for Characterizing Resonance Quality Factor in Superconducting Resonators
Abstract: We present a study on tunable Fano-type resonances in a superconducting coplanar cavity coupled to multiple artificial atoms [1,2]. By applying bias current through nearby control lines, the shape of the measured cavity transmission can be continuously tuned, exhibiting Fano-type resonances with a dispersive shift that can be observed as a peak or a dip. We demonstrate how the heating of the environment can invert the line shape of the cavity, and how this Fano-peak inversion is possible due to a tunable interference between a microwave transmission through a background and through the cavity. We also discuss how the background transmission can be accounted for by Jaynes-Cummings type models via modified boundary conditions. Additionally, we investigate the characterization of material losses in superconducting resonators, using a combination of simulation and experiment to determine the reliability of a fitting algorithm for separating internal and coupling quality factors of the resonance quality factor[3,4]. We propose a novel measurement protocol to reduce fitting errors and mitigate the influence of the measurement background on fit results. Our findings provide insights into the tunability and manipulation of Fano-type resonances in superconducting quantum devices and can be generalized for other resonance systems beyond superconducting resonators. [1] Phys. Rev. A 99, 063804 (2019) [2] Phys. Rev. Applied 14, 024025 (2020) [3] Review of Scientific Instruments 86, 024706 (2015) [4] arXiv:2301.06364
Time: Thursday 09/22/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Eva Gurra, JILA National Institute of Standards and Technology, 08/24/2023
Title: Design of a current-biased tunable coupler integrated with superconducting 3D-cavities.
Abstract: Superconducting circuits are a leading platform for scalable quantum information processing. These macroscopic circuits can be easily controlled using magnetic flux generated by delivering current to an off-chip coil or an integrated on-chip coil. However, flux sensitive devices can suffer from flux offsets and environmental magnetic field fluctuations, and cannot be operated inside of superconducting enclosures. Furthermore, scaling up flux-controlled devices can be difficult, as large amounts of current may be required to deliver sufficient flux to each device. One solution for improved operation and scalability is to use current biasing. In this talk, we present the design of a current-controlled superconducting coupling element based on an inductive Wheatstone bridge. The inductors on the arms of the bridge are arrays of gradiometric rf SQUIDs, which are insensitive to uniform flux changes in the environment to first order. The bridge is controlled by a uniform trapped current in the outer loop and imbalanced by a gradiometric current. Numerical simulations of the bridge coupling two superconducting 3D cavities predict that tunable coupling on the order of megahertz, with high on/off contrast, is achievable between the cavities, in several configurations.
Time: Thursday 08/24/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Andrea Morello, Centre for Quantum Computation & Communication Technology, UNSW, 08/10/2023
Title: Quantum Information and Quantum Foundations with Donors in Silicon
Abstract: Dopant atoms in silicon are a versatile platform for experiments in quantum information processing, as well as quantum foundations. The electron [1] and nuclear [2] spin of a 31P donor were the first qubit demonstrated in silicon, and went on to become among of the most coherent qubits in the solid state, with coherence times exceeding 30 seconds [3], and quantum gate fidelities approaching 99.99% [4]. In this talk I will present the state of the art and future directions for donor spins in silicon. For quantum information, the current focus is on multi-qubit operations, scale-up and fault tolerance. We have demonstrated an exchange-based 2-qubit CROT gate for electron spins [5], using a device in which we implanted a high dose of 31P donors. Future experiments will focus on using deterministic, counted single-ion implantation, for which we have recently demonstrated the capability to detect an individual ion with 99.85% confidence [6]. With nuclear spins, we have achieved the landmark result of universal 1- and 2-qubit logic operations with >99% fidelity, and prepared a 3-qubit GHZ entangled state with 92.5% fidelity [7]. We have also demonstrated the coherent electrical control of an electron-nuclear flip-flop qubit [8], which will greatly facilitate the integration of single-atom qubits in nanoelectronic devices. Heavier donors possess a high nuclear spin quantum number, which can be used to study quantum chaos in a single quantum system [9]. Chaotic dynamics must be understood and controlled for the correct operation of quantum computers and quantum simulators [10]. In the process of operating a single 123Sb nucleus, we (re)discovered the phenomenon of nuclear electric resonance, and applied it for the first time to a single nuclear spin [11]. This provides yet another pathway to scale up and integrate donor-based quantum technologies.
[1] J. Pla et al., Nature 489, 541 (2012) [2] J. Pla et al., Nature 496, 334 (2013) [3] J. Muhonen et al., Nature Nanotechnology 9, 986 (2014) [4] J. Muhonen et al., J. Phys: Condens. Matter 27, 154205 (2015) [5] M. Madzik et al., Nature Communications 12, 181 (2021) [6] A. Jakob et al., Advanced Materials 34, 2270022 (2022) [7] M. Madzik et al., Nature 601, 348 (2022) [8] R. Savytskyy et al., Science Advances 9, eadd9408 (2023) [9] V. Mourik et al., Physical Review E 98, 042206 (2018) [10] L. Sieberer et al., NPJ Quantum Information 5:78 (2019) [11] S. Asaad et al., Nature 579, 205 (2020)
Time: Monday 08/14/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Joanna Zajac, Brookhaven National Lab, 08/10/2023
Title: Indistinguishable single photons for QIST Applications
Abstract: A key ingredient for quantum technologies is an on-demand source of indistinguishable single photons. State-of-the-art indistinguishable single-photon sources typically employ resonant excitation pulses with fixed repetition rates, creating a string of single photons with predetermined arrival times. However, in future applications, an independent electronic signal from a larger quantum circuit or network will trigger the generation of an indistinguishable photon. Further, operating the photon source up to the limit imposed by its lifetime is desirable. Here, I discuss our work on III-V QDs for generating a true on-demand approach with detailed control of the excitation pulse duration based. I will discuss dephasing mechanisms and demonstrate that highly indistinguishable single photons can be generated using this on-demand approach. I will also discuss their future use for the hybrid quantum networks.
Time: Thursday 08/10/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Will Zeng, Unitary Fund, 08/09/2023
Title: What we need for useful quantum computers and how to get there: error mitigation
Abstract: Quantum computers have theoretical promise as useful industrial and scientific tools. This talk will be in two parts. In the first, we will use finance applications of simulation and optimization as a case study to estimate the performance of a quantum computers that would be needed for useful advantage. This work indicates that significant reductions in error rates are needed. In the second part of the talk, we will review new error mitigating techniques for compiling quantum programs to be robust against errors. We review the role these error mitigating techniques could play with quantum error correction to make needed error reductions.
Time: Wednesday 08/09/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Jesse Amato-Grill, QuEra, 08/08/2023
Title: Quantum Computing with Neutral Atoms
Abstract: Neutral atom arrays have recently emerged as one the leading platforms for large-scale quantum computing and simulations [1, 2]. These systems offer a variety of possible qubit encodings with long coherence times, as well as exceptional programmability and reconfigurability of the array geometry and connectivity. In addition, strong, highly coherent coupling between the qubits can be achieved using Rydberg states of the atoms. In the last year, QuEra Computing’s Aquila came online as the first commercially available neutral atom quantum computer. Aquila is a 256-qubit analog-mode device based on a 2D array of Rubidium-87 atoms in reconfigurable optical tweezers. I will tell the story of how it was built, review its performance [3], and discuss prospects for digital and error-corrected neutral atom devices. [1] L. Henriet et al., Quantum 4, 327, (2020). [2] S. Ebadi et al., Science 376, 1209-1215 (2022). [3] https://arxiv.org/abs/2306.11727 \
Time: Tuesday 08/08/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Connor Hart, Quantum Catalyzer, 07/25/2023
Title: Magnetic Imaging using the Quantum Diamond Microscope
Abstract: The Quantum Diamond Microscope (QDM) leverages nitrogen-vacancy (NV) defects in diamond for wide-field imaging of magnetic fields, with applications spanning geoscience, life science, material science, and quantum technology education. In this talk, I will introduce the technology, including the underlying NV physics, and highlight recent scientific results enabled by quantitative, micron-scale magnetic imaging using the QDM. To conclude, I will describe our recent commercialization efforts at Quantum Catalyzer and the approach we are taking for transitioning technologies out the lab.
Time: Tuesday 07/25/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Tuhin Dey, Texas State University, 06/29/2023
Title: Growth of Germanium Tin Carbide Alloy: Possible Photonic Materials for Lasers and Amplifiers
Abstract: Electronic and photonic integrated circuits (EPICs) are based on replacing slow, passive elements of ICs, such as copper interconnects, with optical elements for greater speed. One way to implement this is to directly integrate optically active devices such as lasers and amplifiers into integrated circuits (ICs). There are some existing techniques to integrate laser sources on Integrated Metal Oxide Semiconductors (CMOS), but they all utilize III-V laser materials. From a material science point of view, a single material system would provide maximum speed in EPICs because it would allow smaller devices to be placed directly within the silicon circuit. Thus, there has been an increasing focus on advancing Group IV semiconductor optoelectronic devices compatible with the CMOS platform. The inherent challenge lies in the indirect bandgap nature of Group IV materials, which hinders radiative recombination rates, resulting in low quantum efficiency and high threshold current. This limits the use of Group IV materials to any photonic applications. However, germanium (Ge) has a nearly direct bandgap: the energy difference between the direct and indirect bands is very small (~136 meV). Therefore, with the help of strain or alloying, one can easily tune the band structure of Ge and make it a direct bandgap material. Unlike III-V materials, the new material is compatible with the fabrication of Si electronics. In this presentation, I will discuss the high-quality growth of tensile-strained pseudomorphic Ge1 x ySnxCy alloy at low temperatures by molecular beam epitaxy (MBE) to develop direct bandgap Group IV materials. The alloy was investigated thoroughly using High-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Rutherford backscattering spectroscopy (RBS). Through these techniques, a comprehensive understanding of the growth mechanism of GeSnC has been achieved. Lastly, I will show how optical absorption and photoluminescence (PL) results show the possible direct bandgap nature of GeSnC.
Time: Thursday 06/29/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Philip Moll, Max-Planck-Institute, 06/28/2023
Title: The unusual electron transport in metallic Kagome nets
Abstract: Materials that can host different states of electronic order form a recurring theme in physics and materials science, and they are of particular interest if they are coupled strongly. A famous example are ferroelectrics, in which electric polarization and magnetism not only coexist but are strongly linked. This both unveils a rich physics of correlated states, and also opens unexpected application avenues as the coupling promises to manipulate one state by a stimulus that primarily acts on another – say switching magnetism using electric fields. Recently, materials based on the structural motif of the Kagome web have attracted significant attention for their tendency to host such strongly coupled phases. In particular, the centro-symmetric layered Kagome metal (K,Cs)V3Sb5 have entered the focus of experimental and theoretical research. They host a charge-density-wave type transition at elevated temperatures ~100K, followed by a superconducting transition at 3K (exact values depend on composition). Yet there is another type of electronic order which thus far eludes exact microscopic identification. A series of experimental probes detects the onset of anomalous behavior around T’~30-40K, including thermal Hall, SR, NMR, magnetic torque, Kerr rotation. The anomalous low-temperature state carries the characteristics of a chiral, nematic and time-reversal-symmetry breaking fluid (all of which are under most active debate currently). Yet what crystallizes out of the current state of experimental data is a highly entangled system which is extraordinarily responsive to external perturbations. This materials main strength is equally its weakness, the unusual degree of coupling between states can hinder its systematic investigation. However, it is already clear that it provides a platform to explore strongly coupled correlated phases, and as a result it displays a thus-far unknown electromagnetic response, a diode in which the forward direction can be switched by the application of a magnetic field. I will review the current state of the field, and discuss ongoing projects in my department.
Time: Thursday 06/28/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Gabriella Carini, Brookhaven National Laboratory, 06/27/2023
Title: QIST at BNL: a network of opportunities.
Abstract: BNL continues to advance quantum computing beyond the current noisy intermediate scale quantum (NISQ) limitations, discover next generation quantum materials, and develop an entanglement-sharing quantum network as the basis for the first prototype of the quantum internet. A short overview of several activities with emphasis on quantum networks will be presented.
Time: Thursday 06/28/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
John Davis, University of Alberta, 05/25/2023
Title: Sensing Gravitational Waves and Dark Matter with Superfluid Helium
Abstract: Observations spanning multiple astronomical scales point to the existence of an unknown form of matter, dubbed “dark matter”, that constitutes over 85% of the mass of most galaxies. Recent theoretical insights into the possible nature of dark matter and how it interacts with normal matter have inspired a wide range of experimental efforts aimed at directly detecting dark matter. As part of this effort, we are developing small-scale experiments to search for multiple well-motivated “ultralight” dark matter candidates, placing much stronger bounds than are currently possible with high-cost and/or large-scale efforts. The core enabling technology relies on quantum-limited microwave cavity readout of mechanical motion in superfluid helium. I will tell you about the experiments that have led up to where we are now, and our current efforts with regards to this table-top dark matter search.
Time: Thursday 05/25/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Swarnadeep Majumder, IBM, 05/23/2023
Title: Characterizing and mitigating coherent errors in quantum computers
Abstract:In this talk, we will discuss novel methods for characterizing and mitigating coherent errors in quantum computers. We will then delve into the basics of characterizing noise in quantum computers and explore the use of quantum control and error mitigation techniques to reduce the impact of noise on performance. The focus of the first part of the talk will be on a particularly detrimental type of time-dependent errors and the derivation of theoretical limits of a closed-loop feedback based quantum control protocol for their mitigation. We will present two different protocols, one suitable for fault-tolerant systems and another for near-term devices, and demonstrate their performance through numerical simulations. In the second part, we will discuss the mitigation of coherent noise at the circuit level through the use of the hidden inverses protocol, with results from experiments conducted at Duke University, Sandia National Laboratories, and IBM. Overall, this talk will provide insights into the challenges of building and operating quantum computers with coherent errors, and the promising methods being developed to mitigate errors and improve their performance.
Time: Tuesday 05/23/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Valla Fatemi, Cornell University, 05/18/2023
Title: Probing Andreev bound states with circuit quantum electrodynamics.
Abstract:Andreev bound states (ABSs), the quantum many-body electronic states that are localized at Josephson weak-links, provide a platform to explore the interplay of superconductivity, spin-orbit interaction, Coulomb interaction, and magnetism, including in topological regimes. ABS carry supercurrent and are thus suited to being probed by the circuit quantum electrodynamics (cQED) toolset, which offers high- resolution, high-bandwidth microwave-domain measurement and manipulation of quantum states. In this talk, I will describe our implementation of cQED to reveal the spectrum, dynamics, and potential applications of quasiparticles trapped in ABSs hosted in a Josephson semiconductor nanowire. After an introduction comparing quantum superconducting circuits and ABS, I will motivate ABS as a unique qubit platform. Then, I will describe our use of superconducting resonators for quantitative measurement of microwave response functions and spectroscopy in the presence of non-equilibrium state populations. With this tool, we developed insights on Coulomb interaction in ABSs, which are conventionally regarded as chargeless states. Furthermore, I will describe how we leveraged the physics of spin-orbit interaction to realize the Andreev spin qubit, a supercurrent-carrying spin degree of freedom.
Time: Thursday 05/16/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Mark Nowakowski, Boeing, 05/16/2023
Title: Demystifying STEM Career Opportunities
Abstract: IResearch-focused graduate students and postdoctoral fellows seeking permanent career opportunities commonly encounter a STEM job market landscape that can offer a wide breadth of opportunities; however, identifying opportunities that offer the best “fit” and navigating the application process can, on occasion, seem unexpectedly challenging. This presentation aims to provide realistic and honest guidance to students who are either planning or within the process of a STEM career job search. First, the landscape of career opportunities and pathways available to higher education students is surveyed through a detailed contrast of the skillsets that may be sought after for positions in academia, national labs, and industry. Special consideration is then offered to illuminate the value, potential roles, and sought-after experience of higher education graduates who pursue research opportunities within industry. Finally, a detailed discussion regarding the application process is presented that provides insight into how job requisitions are created, the processes that may influence candidate down- selection, and the rigor required to prepare documents for STEM applications in academia, national labs, and industry.
Time: Tuesday 05/16/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Sebastian Will, Columbia, 05/11/2023
Title: Quantum Control of Atoms and Molecules for Quantum Science and Technology.
Abstract:Quantum systems that are highly controllable, scalable, and preserve quantum properties for extended periods of time are the key driver of the second quantum revolution. Atoms and molecules – pristine miniature quantum systems provided by Nature – have extremely promising properties in this regard. In this talk, I will discuss our recent progress in synthesizing, controlling, and stabilizing dipolar molecules of NaCs [1,2,3]. The dipolar interactions between NaCs molecules have long-range character and are ideally suited for the preparation of strongly correlated and highly entangled quantum states. Most recently, we have demonstrated that rotational qubits in NaCs can be controlled via microwave pulses on the nanosecond-scale, rivaling the control times of many traditional qubit platforms. In addition, we have demonstrated that microwave shielding can enhance the lifetime of dense NaCs ensembles by a factor of 100. NaCs now provides us with a wide range of opportunities, including the formation of novel quantum phases, such as 2D quantum crystals, and the quantum simulation of spin systems. Finally, I will present our effort on creating optical tweezer arrays of strontium atoms, realizing a powerful new platform for precision time-keeping, quantum simulation, and quantum computing [4]. [1] I. Stevenson et al., Ultracold Gases of Dipolar NaCs Ground State Molecules, arXiv:2206.00652 (2022). [2] A. Lam et al., A High Phase-Space Density Gas of NaCs Feshbach Molecules, Phys. Rev. Research 4, L022019 (2022). [3] C. Warner et al., Overlapping Bose-Einstein Condensates of Na and Cs, Phys. Rev. A 104, 033302 (2021). [4] “Metasurface Holographic Optical Traps for Ultracold Atoms,” X. Huang et al. arXiv:2210.07425 (2022).
Time: Thursday 05/11/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
John Davis, University of Alberta, 04/27/2023
Abstract: Observations spanning multiple astronomical scales point to the existence of an unknown form of matter, dubbed “dark matter”, that constitutes over 85% of the mass of most galaxies. Recent theoretical insights into the possible nature of dark matter and how it interacts with normal matter have inspired a wide range of experimental efforts aimed at directly detecting dark matter. As part of this effort, we are developing small-scale experiments to search for multiple well-motivated “ultralight” dark matter candidates, placing much stronger bounds than are currently possible with high-cost and/or large-scale efforts. The core enabling technology relies on quantum-limited microwave cavity readout of mechanical motion in superfluid helium. I will tell you about the experiments that have led up to where we are now, and our current efforts with regards to this table-top dark matter search.
Bio: John P. Davis is a Professor in the Department of Physics at the University of Alberta. His group specializes in cavity optomechanics and electromechanics at low-temperatures, in particular for the study of superfluids, superconductors, and magnetic materials. He obtained his Master’s and Ph.D from Northwestern University in Evanston, Illinois in 2003 and 2008, respectively, studying superfluid 3He. Before that he graduated summa cum laude in physics from Washington University in St. Louis, Missouri. He was awarded the Sloan Research Fellowship in 2013 and has won a number of awards at the University of Alberta. He is currently director of the Quanta CREATE program funded by NSERC and CTO of Zero Point Cryogenics, a North American manufacturer of dilution refrigerators and related cryogenic equipment.
Time: Thursday 04/27/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Alireza Seif, IBM, 04/13/2023
Title: Entanglement negativity transition with measurement and feedforward: From quantum to classical dephasing dissipatio
Abstract: In monitored quantum systems, where the dynamics consist of both measurements and unitary time evolution, the state of the system conditioned on measurement outcomes, also known as a trajectory, can be highly entangled. However, this entanglement is often obscured when we look at the unconditional state averaged over measurement outcomes. In this work, we show that the entanglement in trajectories can be revived in the unconditional state using local operations and classical communications. We uncover a sharp transition in the entanglement negativity of the unconditional state as a function of the number of measurement and feedforward channels acting on the system. The unconditional dynamics can also be viewed as the evolution of the system interacting with an environment, and the entanglement transition can be interpreted as a classical-to-quantum transition of the environment. We use tools from random matrix theory together with numerical simulations to shed light on the mechanism of this transition. Finally, we discuss an experimental protocol for observing this transition in engineered quantum devices.
Time: Thursday 04/13/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Emanuel Tutuc, University of Texas at Austin, 03/30/2023
Title: Tunneling and Interlayer Coherence in Twist-Controlled vander Waals Heterostructures
Bio:Van der Waals (vdW) heterostructures of two-dimensional materials offer an unprecedented playground to combine materials with different electronic properties, without the constraints of lattice matching associated with epitaxial growth. Recent years have witnessed the emergence of interlayer twist as a new parameter that control the electronic properties of vdW heterostructures. We provide an overview of experimental techniques to control interlayer twist, along with examples from moiré patterns and twist-controlled double layers. We show that interlayer tunnelling serves as unique tool to probe interlayer coherence in twist-aligned, closely spaced double layers where interaction leads to a coherent superposition of electronic states in individual layers, with Josephson junction-like tunnelling characteristics robust to temperature, and layer density detuning.
Time: Thursday 03/30/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Peter Schüffelgen, Forschungszentrum Jülich, 03/16/2023
Title: (Bi,Sb)2Te3 as a potential platform for future topological qubits
Bio: (Bi,Sb)2Te3 is a versatile topological material with a naturally occurring spinless helical gap that can reach up to 300 meV. However, the utility of its topological properties in quantum devices is hindered by its tendency to rapidly oxidize under ambient conditions. In this talk, I will present a novel ultra-high vacuum lithography technique that can be utilized for the in-situ fabrication of a range of quantum devices.
Time: Thursday 03/13/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
[No seminar] [APS March meeting], 03/09/2023
Stephanie Lee, New York University, 03/02/2023
Title: Twisted Organic Semiconductor Crystals
Abstract: Molecular crystals that twist as they grow are common but little known and introduce completely unexplored features to materials design. Here, we present growth-induced twists to molecular semiconductor crystals with the expectation that microstructure and continually precessing crystallographic orientations can modulate interactions with light, charge transport, and other optoelectronic processes. We have found that a variety of organic semiconductors and charge transfer complexes can be readily induced to grow from the melt as spherulites of tightly packed helicoidal fibrils. The twisting pitch can be controlled by the degree of undercooling after melting or through the incorporation of additives. Intriguingly, charge mobilities measured using field-effect transistor platforms have been found to increase with increasing extent of twisting. Photoluminescence intensity is also modulated by crystal twisting, with some orientations exhibiting stronger PL signal compared to others. These results indicate crystal twisting to be a promising strategy for modulating the performance of optoelectronic devices.
Time: Thursday 03/02/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Saien Xie, Princeton University, 02/16/2023
Title: Atomically Engineered Thin Films and Devices
Abstract: Thin film materials and heterostructures play a key role in modern technology including electronics and photonics. Atomically precise engineering of thin film materials enables unprecedented control of their structure and properties, bringing exciting opportunities to future materials and devices. Transition metal dichalcogenides (TMDs), which form three-atom-thick monolayers with van der Waals surfaces, provide an ideal material platform with diverse electrical and optical properties for thin film engineering in the atomically thin limit. In this talk, I will discuss three key synthesis challenges for realizing atomically engineered thin films and superlattices with atomically thin TMDs. Firstly, I will discuss how high-performance monolayer TMD films can be synthesized with wafer-scale uniformity. Furthermore, I will discuss how dissimilar TMDs (e.g. tungsten disulfide and tungsten diselenide) can be integrated laterally in the monolayer plane to form superlattices without dislocations, despite a large 4% lattice mismatch. Lastly, I will discuss how various TMD monolayers can be stacked vertically to form superlattices with designed properties. These scalable synthesis capabilities will further enable novel atomically engineered materials that hold great potential for future ultrathin electronics.
Time: Thursday 02/16/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Vinod Menon, City College of New York, 02/09/2023
Title: Half-light half-matter quasiparticles: from condensation to quantum nonlinearity
Abstract: Strong light-matter interaction results in the formation of half-light half-matter quasiparticles called polaritons that take on the properties of both its constituents. In this talk I will first introduce the concept of strong light-matter coupling in low-dimensional semiconductors in optical cavities followed by discussion of realizing Bose Einstein like condensates at room temperature using polaritons. Following this, I will present our recent work on polaritons in 2D materials and their potential to reach quantum nonlinearity. Time permitting, I will discuss the potential of cavity coupling as a means to engineer quantum materials.
Time: Thursday 02/09/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Kaitlyn Morrell, University of North Carolina at Chapel Hill, 02/02/2023
Title: The Quantum Thermodynamics Computational Engine
Abstract: Though studied for decades, the quantum many-body problem remains at the forefront of theoretical research, where the goal of understanding systems of numerous quantum particles is common to astro-, atomic, nuclear, and condensed matter physics. Recently, experimental advances have paved the way for probing quantum systems in new regimes. Accordingly, efforts to tackle the many-body problem from the theoretical side have grown, resulting in a variety of methods, each with their own strengths and weaknesses. Such methods generally fall into two categories: analytic and numerical. In this talk, I present the Quantum Thermodynamics Computational Engine, which bridges the two by implementing an automated algebra approach, followed by semi-analytic integration. With this tool, we study a non-relativistic, spin-1/2 fermionic system with a contact interaction, in a regime relevant for ultracold atoms and dilute neutron matter. The interaction is accounted for using a quantum cumulant expansion whose coefficients are generated automatically based on a generating functional formalism. Results for the equation of state in the strongly interacting regime are presented and the future outlook of the method is discussed.
Time: Thursday 02/02/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Ravi Pillarisetty, Intel, 01/26/2023
Title: Industry perspective on quantum and cryogenic computing hardware
Abstract: The unprecedented technological rise around cloud computing is transforming daily life and revolutionizing the way businesses leverage technology and data to add value for their customers. With worldwide data generation growing to over 64 zettabytes/year, recent hardware innovations around CPU, FPGA, GPU, TPU, and neural processing units have pushed compute efficiency by 5 orders of magnitude to over 100 TOPs/W. However, to continue this exponential trajectory beyond the era of hyperscaling in the data center, emerging technologies around quantum and cryogenic computing will need to play a central role. Quantum computing’s potential to solve currently intractable problems has generated tremendous interest across all segments of the economy. At Intel, we are leveraging our rich history of Moore’s Law innovations to drive the development of a scalable qubit system. This includes the creation of a full 300mm device-integration line for building silicon-based spin qubits arrays, along with the corresponding high-volume cryogenic electrical characterization infrastructure. Additionally, we will discuss cryogenic computing applications both for quantum and traditional compute. Here we review Cryo CMOS chip design and system integration to enable qubit control and read out on the 4K stage of the fridge, which eliminates the need for external room temperature electronics. Finally, we examine both CMOS and non-CMOS based devices and circuits and their applicability towards energy savings for traditional compute in the data center.
Time: Thursday 01/26/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Enrico Rossi, Department of Physics, The College of William and Mary, 01/23/2023
Title: Leggett Modes in Dirac Semimetals
Abstract: Leggett modes are exemplary of the unusual effects that can be present in multiband superconductors. A Leggett mode describes the collective periodic oscillation of the relative phase between the phases of the superconducting condensates formed by electrons in different bands. It can be thought of as the mode arising from an inter-band Josephson effect. The experimental observation of Leggett modes is challenging given that they describe charge fluctuations between bands and therefore are hard to probe directly. In this talk I will present how Leggett modes can be detected unambiguously in a.c. driven superconducting quantum interference devices (SQUIDs). I will then show how measurements taken on a SQUID based on the Dirac semimetal Cd3As2 exhibit the theoretically predicted signatures of Leggett modes and therefore allow us to conclude that a Leggett mode should be present in superconducting Cd3As2.
Time: Thursday 01/23/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Faranak Bahrami, Boston College, 01/19/2023
Title: Tuning the Low-Energy Physics in Honeycomb Kitaev Magnets
Abstract: Nearly two decades ago, Alexei Kitaev proposed a two-dimensional model on a honeycomb lattice with bond-directional interactions for spin-1/2 particles which had the potential to host a quantum spin-liquid (QSL) ground state. This work initiated numerous investigations to design and synthesize candidate materials, eventually leading to the introduction of the first generation of Kitaev materials such as Na2IrO3, α-Li2IrO3, and α-RuCl3. All these known Kitaev candidates displayed additional, non-Kitaev interactions such as the Heisenberg and off-diagonal exchange interactions and thus failed to satisfy all the desired properties of the theoretical model. In this talk, I will discuss the results of some of my Ph.D. research on the structural modification of first generation Kitaev magnets via topochemical methods. This research has revealed that the magnetic properties of these materials are highly dependent on the unique combination of structural and spin-orbital properties found in each candidate material. As two specific examples, I will explain how the structural modification via topotactic exchange reactions can alter the magnetic interactions in favor of a QSL phase[1,2], or can lead to the realization of novel low-energy physics [3].
[1] Bahrami, et al. “Thermodynamic evidence of proximity to a Kitaev spin liquid in Ag3LiIr2O6.” PRL 123, 237203 (2019).
[2] Bahrami, et al. “Effect of structural disorder on the Kitaev magnet Ag3LiIr2O6.” PRB 103, 094427 (2021).
[3] Bahrami, et al. “First demonstration of tuning between the Kitaev and Ising limits in a honeycomb lattice.” Sci. Adv. 8, eabl5671 (2022).
Time: Thursday 01/19/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Nate Gemelke, Co-founder and CTO of QuEra, 01/12/2023
Title: Thinking geometrically: how flexibility in qubit geometry helps find efficient quantum solutions to useful problems
Abstract: Solving classical problems geometrically is sometimes easier than using algebra or calculus. Perhaps surprisingly, the same is also true of quantum computing. When using computing architectures that allow for flexibility in the geometrical arrangement of qubits, such architectures can solve some problems more efficiently than gate-based implementations. Furthermore, given the current fidelity and noise challenges of gate-based systems, a geometrical solution might be the only one that is feasible today. The talk will provide some useful examples and also provide an update on the progress and deployment of the QuEra neutral atom machine, now available on Amazon Braket.
Time: Thursday 01/12/2023, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Marianna Bonanome, Head of Education Outreach, Specialty: Quantum Algorithms, Combinatorial Group Theory, Quantum Education 12/15/2022
Title: Quantum Algorithms for Fixed Points and Invariant Subgroups
Abstract: In 1982 Richard Feynman and Paul Benioff independently observed that a quantum system can perform a computation. This has opened the door to a change in paradigm from classical to quantum computation. Algorithms designed to run on quantum processors have the potential to solve problems efficiently where classical algorithms cannot. In particular, we introduce problems in the field of combinatorial group theory concerning fixed points and invariant subgroups of automorphisms and we apply quantum algorithms to solve them. These efficient algorithms invoke a quantum algorithm which computes the intersection of multiple unsorted multisets whose elements originate from the same set. This intersection algorithm is an application of the Grover search procedure.
Time: Thursday 12/15, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Moty Heiblum, Department of Condensed Matter Physics, Weizmann Institute of Science, Israel 12/13/2022
Title: Determination of the Topological Order of a Non-Abelian Quantum State, The 5/2 FQHE State
Abstract: Studying non-abelian anyons is exciting due to their unique braiding statistics. The 5/2 quantum Hall state has been long proposed to host such localized quasiparticles in the 2D bulk. Resting on ‘bulk-edge’ correspondence, their gapless edge modes are expected to mirror the topological order of the 5/2 quantum state. Supporting an odd number of Majorana (neutral) modes guarantees the non-abelian nature of the state.
Time: Tuesday 12/13, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Saulius Vaitiekėnas, Center for Quantum Devices, Niels Bohr Institute | University of Copenhagen 12/12/2022
Title: Magnetic-domain driven 0-π transition in hybrid nanowire Josephson junctions
Abstract: I will discuss transport measurements in semiconducting InAs nanowires with epitaxial ferromagnetic insulator EuS and superconducting Al coatings. Hybrid Josephson junctions comprised of such wires display a hysteretic superconducting window close to the coercivity, away from zero external magnetic field. Within this window, we find an abrupt switch between π and 0 phases that we attribute to the discrete flipping of the EuS domains—a new mechanism that hasn’t been reported before.
Time: Monday 12/12, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Andrea Cavalleri, Max Planck Institute for the Structure and Dynamics of Matter | Department of Physics, University of Oxford, 12/09/2022
Title: Photo-induced High Temperature Superconductivity
Abstract: I will discuss how coherent optical pulses at mid infrared frequencies can be used to excite targeted molecular vibrations in organic materials with strongly correlated electrons and manipulate their electronic properties. I will discuss especially the case of charge transfer salts and of doped fullerites. Both materials exhibit colossal increase in carrier mobility for certain vibrational excitations and key signatures of photo-induced high temperature superconductivity.
Time: Friday 12/09, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Zlatko K Minev, IBM Quantum, 11/17/2022
Title: Learning and inverting quantum noise: Probabilistic error cancellation with sparse Pauli-Lindblad models on noisy quantum processors.
Time: Thursday 11/17, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Domenico Di Sante, Università di Bologna, 11/10/2022
Title: Deep Learning the Functional Renormalization Group Flow for Correlated Fermions
Abstract: I will present a data-driven dimensionality reduction of the scale-dependent 4-point vertex function characterizing the functional Renormalization Group (fRG) flow for the widely studied two-dimensional t − t′ Hubbard model on the square lattice. It will be shown that a deep learning architecture based on a Neural Ordinary Differential Equation solver in a low-dimensional latent space efficiently learns the fRG dynamics that delineates the various magnetic and d-wave superconducting regimes of the Hubbard model. In addition, a Dynamic Mode Decomposition analysis confirms that a small number of modes are indeed sufficient to capture the fRG dynamics. This talk will demonstrate the possibility of using artificial intelligence to extract compact representations of the 4-point vertex functions for correlated electrons, a goal of utmost importance for the success of cutting-edge quantum field theoretical methods for tackling the many-electron problem. Besides the specific application to correlated fermions, I will discuss a dimensionality reduction scheme that may be useful to any research field dealing with presumable very high-dimensional data. Reference: Phys. Rev. Lett. 129, 136402 (2022).
Time: Thursday 11/10, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Amine Assouel, ENS Paris-Saclay, Gif-sur-Yvette, France, 10/6/2022
Title: A quantum generative adversarial network for distributions
Abstract: Recent advances in Quantum Computing have shown that, despite the absence of a fault-tolerant quantum computer so far, quantum techniques are providing exponential advantage over their classical counterparts. We develop a fully connected Quantum Generative Adversarial network and show how it can be applied in Mathematical Finance, with a particular focus on volatility modeling.
Time: Thursday 10/06, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Leila Jabdaraghi, Aalto University, Finland, Thursday 9/15/2022
Title: Magnetometry by a proximity Josephson junction interferometer and fabrication of superconducting quantum devices’
Abstract: In quantum technology, several aspects of superconductivity such as proximity effect have been studied to develop a wide range of attractive applications at sub-kelvin temperatures- A SQUIPT interferometer relies on the phase dependence of the density of states in the proximized weak link. These devices offer the possibility to realize sensitive low-dissipation magnetometers. First part of this talk covers the development of the sensitive SQUIPT magnetometers. Considering non-hysteretic SQUIPTs with enhanced responsivity, investigation of a prototype device based on Nb-Cu-Nb SNS junction with a conventional Al probe in tunnel junction (Nb-SQUIPT). Consequently, I will present the flux noise characterization of the device using simultaneous measurement of DC transport properties and shot noise. Finally, as examples of current activities in VTT I will provide fabrication methods for some selected quantum devices implementing in superconducting quantum circuits.
Time: Thursday 09/15, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Fred Shi, NYU/Princeton, Thursday 9/8/2022
Title: Adiabatic quantum computing on quantum annealers: an brief introduction
Abstract: Adiabatic quantum computing is a promising technology to solve classically hard problems more efficiently than state-of-the-art classical computing algorithms with the power of quantum annealing process. Quantum annealing process is an application of the quantum Adiabatic theorem and the physics evolution during the process would lead to the ground state configuration of a complicated Hamiltonian that can encode optimization problems, making it a potential application for quantum speed up in finding the global minimal of exponentially hard optimization problems. Instead of universal quantum computers, quantum annealers are the hardware for adiabatic quantum computing. They are like quantum application-specific integrated circuits (ASIC) rather than a quantum CPU, making state of the art machines to have orders of magnitudes more qubits than that of a quantum computer. In this talk I will introduce the physics of quantum annealing and discuss the advantages and bottlenecks of the adiabatic quantum computing. We will also briefly talk about how to map different interesting problems, including NP-complete problems, that have real world applications onto the current generation quantum annealers.
Time: Thursday 09/08, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Mehdi Namazi, Qunnect, Thursday 8/25/2022
Title: Efficient Distribution of Quantum Entanglement Over Fiber Networks
Abstract: Distributing quantum entanglement is the backbone of the future quantum internet. To do so efficiently, many hardware such as quantum sources, memories and swapping modules must be interfaced together using fiber and free space links. For this talk I will briefly overview the global effort in brining these networks into reality. This will be followed by a deeper dive into the work we are doing at Qunnect to develop the infrastructure for entanglement distribution protocols. I will present our work on the development of a bichromatic photon source (one in the telecom band and one at near-IR) based on warm atomic vapors. We characterize the source, and show our progress towards interfacing it with atomic memories. Additionally, I will talk about the interfacing of the source with our Automated Polarization Compensating modules which effectively preserve the purity of entangled photons over long telecom fibers. Together, these modules pave the way towards building a quantum repeater node based on room-temperature technologies, natively well-suited for interfacing with many quantum communication, computation and sensing technologies.
Time: Thursday 08/25, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Gerald Behr, Memorial Sloan Kettering Cancer Center, Thursday 8/18/2022
Title: Magnetic Resonance Imaging: A Radiologist’s Perspective
Abstract: The advent of Magnetic Resonance Imaging (MRI), which is largely based on the principles of Nuclear Magnetic Resonance (NMR), has revolutionized the practice of medicine. Clinical advantages over other imaging modalities include its multiplanar image acquisition capability, it’s unmatched intrinsic contrast between tissue types and its versatility regarding the various tissue properties that it can measure by varying several parameters which are chosen by the user. Traditionally, relative signal magnitude “maps” across a body “slice” can be set to detect differences in either proton density (PD), T1 and T2 time. Based on these parameters alone, the technology is widely used for detection and evaluation of tumors, infection, inflammation, trauma/hemorrhage, bone and joint abnormalities, among other entities. Over the past few decades, more parameters have been successfully measured (beyond T1, T2 and PD), some of which are based on different fundamentals (i.e. magnetic susceptibility, Na+ signal detection, hyperpolarized MRI) and some of which are calculated from traditional measurements (i.e. flow velocity, iron concentration in tissue). Like all imaging modalities, MRI can suffer from distortions with images rendered suboptimal due to limitations related to hardware (i.e. inhomogeneity of the magnetic field), software (i.e. processing of ambiguous signals) or to the patient (i.e. motion, metallic clips, etc). Each of these pose unique problems and have been partially “solved” however there is much room for technologic development. Moreover, data acquisition for MRI remains a slow process which results in 1) Increased susceptibility to motion artifact 2) patient frustration and 3) limits patient throughput which is a financial drain for both hospitals and private imaging centers. The talk will introduce the basic concepts of MRI, illustrate numerous examples of its use, discuss recent advances in the technology and their clinical implications as well as briefly outline areas for future work with emphasis on unmet patient needs.
Time: Thursday 08/18, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Nicholas Bronn, IBM, Thursday 8/11/2022
Title: Quantum Simulation on Noisy Superconducting Quantum Computers
Abstract: The simulation of quantum systems was the initial promise of quantum computers around 40 years ago. Since then, small-scale noisy quantum computing prototypes have been constructed, with those consisting of superconducting qubits a currently popular modality. In this talk, I’ll give an overview of superconducting qubits, their control with Qiskit, and an introduction to quantum simulation. As error mitigation is essential in the current era of noisy quantum hardware, we’ll demonstrate an example recently developed as part of Qiskit Research, which facilitates the adoption of these research tools without the need for low-level knowledge of the underlying hardware and software.
Time: Thursday 08/11, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Tom Marshall, Bloomberg, Thursday 8/4/2022
Title: Entanglement and the Density Matrix
Abstract: Entanglement is one of the primary quantum resources that power quantum computing. Entanglement also gives rise to what Einstein famously referred to as “spooky action at a distance”. In quantum mechanics, and especially in quantum computing and information processing, we deal with entanglement every day, and yet its “spooky” nature tends to stay with us in the backs of our minds. In this talk we’ll go through some of the basic mathematical techniques to describe entanglement, focusing on the density matrix as a very convenient formalism. Mechanically, the talk is mainly a review for more advanced students, and a bit of a dive into the deep end of the pool for those less familiar with quantum mechanics, but its purpose is not to teach (or review) materials that are already in many textbooks so much as to give physical insight into the most central (and often confusing) aspects of quantum physics.
Time: Thursday 08/04, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Aurelia Brook and Andreas Tsantilas, New York University, Thursday 7/28/2022
Title: Noisy State-Preparation Algorithms and the Error Mitigation Frontier
Abstract: Recent advancements in quantum algorithms have been significant, yet there is still much to be done in terms of benchmarking noisy quantum computing hardware. Utilizing IBM’s Qiskit software development kit and quantum hardware, we have streamlined a novel way of benchmarking and characterizing error on noisy qubits. We tested the noise levels of IBM’s quantum hardware by implementing the Kitaev-Webb state preparation algorithm (Kitaev et al. 2008). We further examine both the Kitaev-Webb and Klco-Savage (Klco et al. 2019) algorithms to prepare a 1D discrete Gaussian and a symmetric exponential distribution as a pseudo-Gaussian respectively. Such simulations provide insight into dominant sources of noise on quantum chips. However, the challenge in manipulating and maintaining states at quantum scales results in poor performance on these problems, even for shallow circuits. Thus, while both the Kitaev-Webb and Klco-Savage algorithms can produce informative results when implemented for smaller systems, the industry standard protocol (Randomized Benchmarking) was comparatively shown to be the most scalable measure for noise benchmarking. Next, we discuss these results in the context of “error mitigation,” or the technique of combining classical methods with quantum computation to achieve more accurate expectation values of observables. We give an overview of the subject, talking about Richardson extrapolation and, more recently, Probabilistic Error Cancellation (PEC). We touch on some challenges and difficulties to mitigating errors, as well as possible future directions to take.
Time: Thursday July 28, 11:00 AM to 12:00 PM EST
Location: 726 Broadway, Room 1067
Fergus Hayes, University of Glasgow Thursday 7/21/2022
Title: A Quantum Search Algorithm for Gravitational Wave Astronomy
Abstract: Gravitational-wave astronomy allows for a new window to observe the universe through, giving us unique insight into astrophysics, cosmology, as well as providing tests of general relativity. Gravitational-wave signals are detected through a process called matched filtering, where the data is compared to a large bank of template signals to determine if any of them match. Some matched filtering searches are limited in their sensitivity by the computational demand of parsing through their whole template bank. This provides a major hurdle to making the long-anticipated discovery of detecting continuous gravitational waves from rotating neutron stars for the first time. Quantum computing has the potential to solve problems that are infeasible on classical devices. We propose a quantum algorithm that combines the commonly used classical matched filtering search with Grover’s quantum search algorithm. Quantum matched filtering offers a speed-up over its classical equivalent that is proportional to the square root of the total number of templates. We demonstrate its application in detecting the first gravitational wave signal GW150914 and detail how it could aid in the discovery of continuous waves.
Time: Thursday July 21, 11:00 AM to 12:30 PM EST
Location: 726 Broadway, Room 1067
Kaelyn Ferris, Ohio State University, Thursday 7/14/2022
Title: Practical Quantum Simulation for Quantum Computers
Abstract: Simulating quantum systems is likely to become one of the first practical applications of quantum computers. While numerical simulation relies on approximations in order to make problems tractable for modern computational resources, quantum computation holds the promise of being able to exactly simulate the dynamics of quantum systems. While the field of quantum simulation is nearly as old as quantumcomputing, there remains little introductory material to building quantum simulation algorithms given today’s access to noisy intermediate scale quantum hardware. We review some of the recent advances in simulating quantum systems and prescribe a broad recipe: from encoding a target Hamiltonian to methods of measuring relevant observables and discuss strategies to reduce the effects of noise along the way. By taking advantage of the native cross-resonance gate of IBM’s superconducting hardware and variationally optimizing time evolution operators, we show improvement in the resulting fidelity and accuracy of time evolved systems. One set of measurements in particular, a technique to obtain eigenvalue spectra using a single auxiliary qubit, will also be discussed along with some preliminary results.
Time: Thursday July 14, 11:00 AM to 12:30 PM
Location: 726 Broadway, Room 1067
Jonas Richter, University of College London, Thursday 7/7/2022
Title: Making random circuits useful on noisy intermediate-scale quantum computers
Abstract: Noisy intermediate-scale quantum (NISQ) devices have started to challenge the capabilities of modern supercomputers. An important milestone in this context has been achieved in 2019 by Google’s quantum processor Sycamore, where the Josephson junction-based device was used to sample from the output of a pseudo-random circuit involving up to 53 qubits. In this talk, I will demonstrate that such random circuits are not just abstract tools to achieve a quantum computational advantage, but that this randomness can in fact be a crucial ingredient for useful simulations on today’s NISQ devices. To this end, I will introduce the concept of quantum typicality, which asserts that pure quantum states, drawn at random from a high dimensional Hilbert space, can accurately mimic the properties of the full statistical ensemble. While quantum typicality has already been employed as an efficient numerical method on classical computers, I will particularly focus on our new proposal how quantum typicality can be used for NISQ simulations of challenging problems in quantum many-body physics. Finally, I will provide an outlook on potential future applications, where I will especially discuss two recent implementations on existing quantum hardware which partially build on our proposal. This includes the characterization of a so-called Floquet time crystal on Google’s Sycamore chip as well as the possibility to study finite-temperature properties of quantum materials as explored with IBM’s Quantum Lab. This talk is based on: Jonas Richter and Arijeet Pal, Phys. Rev. Lett. 126, 230501 (2021).
Time: Thursday July 7, 11:00 AM to 12:30 PM
Location: 726 Broadway, Room 1067
Andrew Elkadi, Imperial College London, 06/23/2022
Title: Quantum Generative Adversarial Networks in Option Pricing
Abstract: The topic of Option Pricing has long been explored and researched in classical Finance and Computing. Recent advancements in Quantum Algorithms have made it possible to consider the problem from a Quantum perspective and leverage the field’s inherent non-determinism. In this presentation I will explore how a transfer into the Quantum world can provide an alternative means of calculating prices in a potentially more efficient manner. In particular, I will cover the pairing of Quantum Generative Adversarial Networks and Quantum Monte Carlo Simulations to represent and evolve the underlying distributions of assets which we wish to model for pricing.
Time: Thursday June 23th, 11:00 AM to 12:30 PM
Location: 726 Broadway, Room 1067
Classiq Software Company, Thursday 06/16/2022
Classiq (https://www.classiq.io) giving a demo of their software. More details from the company’s website: https://classiquantum.com/reference/index.html
Time: Thursday June 16th, 11:00 AM to 12:30 PM
Location: 726 Broadway, Room 1067
Javier Robledo Moreno, New York University, Thursday 06/09/2022
Title: Representation of quantum states using neural networks: applications in physics, quantum computing and chemistry
Abstract: In recent years, the use of neural-network representations of quantum states has been proven to be a powerful tool for the variational simulation of quantum systems. Applications range from the understanding of the ground state physics of quantum magnets and fermionic quantum systems like molecules, to the simulation of quantum dynamics or the approximation of quantum states in quantum computers. In this presentation I will review the key concepts necessary to understand this emerging field, including Monte Carlo techniques, neural networks, with a special emphasis on the representation of fermionic quantum states.
Time: Thursday June 9th, 11:00 AM to 12:30 PM
Location: 726 Broadway, Room 1067
Andras Bako, Bloomberg, Thursday 05/19/2022
1. Software Architecture and improvement for quantum monte carlo for derivatives pricing
2. Quantum Machine Learning for regression models to price financial products
3. Physics-Informed Machine Learning with quantum Fourier neural operators, PDE solving