Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G68: Superconducting Qubit Quantum Simulation and AlgorithmsFocus
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Sponsoring Units: DQI Chair: David McKay, IBM TJ Watson Research Center Room: Four Seasons 4 |
Tuesday, March 3, 2020 11:15AM - 11:51AM |
G68.00001: Quantum Supremacy: Benchmarking the Sycamore Processor Invited Speaker: Kevin Satzinger The promise of quantum computers is that certain computational tasks might be executed exponentially faster on a quantum processor than on a classical processor. A fundamental challenge is to build a high-fidelity processor capable of running quantum algorithms in an exponentially large computational space. Here we report the use of a processor with 53 programmable superconducting qubits. In our Sycamore processor, each qubit interacts with four neighbors in a rectangular lattice using tunable couplers. A key systems engineering advance of this device is achieving high-fidelity single- and two-qubit operations, not just in isolation but also while performing a realistic computation with simultaneous gate operations across the entire processor. We benchmark the Sycamore processor using cross-entropy benchmarking, a scalable method to evaluate system performance. Our largest system benchmarks feature circuits that are intractable for classical hardware, culminating in the demonstration of quantum supremacy. Furthermore, the fidelities from full-system benchmarks agree with what we predict from individual gate and measurement fidelities, verifying the digital error model and presenting a path forward to quantum error correction. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G68.00002: Quantum supremacy using the Sycamore processor Charles Neill The promise of quantum computers is that certain computational tasks might be executed exponentially faster on a quantum processor than on a classical processor. A fundamental challenge is to build a high-fidelity processor capable of running quantum algorithms in an exponentially large computational space. Recently, our team has demonstrated a dramatic speedup relative to all known classical algorithms providing an experimental realization of quantum supremacy on a computational task. In this talk, I will focus on the hardware details of the Sycamore processor and how this device enabled supremacy-quality two-qubit gates. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G68.00003: Quantum simulation in circuit QED: Observation of quantum many-body effects due to zero point fluctuations in
superconducting circuits - I: Theory Nicolas Roch, Sebastien Leger, Javier Puertas, Karthik Srikanth Bharadwaj, Remy Dassonneville, Jovian Delaforce, Farshad Foroughi, Vladimir Milchakov, Luca Planat, Olivier Buisson, Cécile Naud, Wiebke Hasch-Guichard, Serge Florens, Izak Snyman Electromagnetic fields possess zero point fluctuations (ZPF) which lead to observable effects such as the Lamb shift and the Casimir effect. In the traditional quantum optics domain, these corrections remain perturbative due to the smallness of the fine structure constant. To provide a direct observation of non-perturbative effects driven by ZPF in an open quantum system we wire a highly non-linear Josephson junction to a high impedance transmission line, allowing large phase fluctuations across the junction. Consequently, the resonance of the former acquires a relative frequency shift that is orders of magnitude larger than for natural atoms. Detailed modelling confirms that this renormalization is non-linear and quantum. Remarkably, the junction transfers its non-linearity to about 30 environmental modes, a striking back-action effect that transcends the standard Caldeira-Leggett paradigm. This work opens many exciting prospects for longstanding quests such as the tailoring of many-body Hamiltonians in the strongly non-linear regime, the observation of Bloch oscillations, or the development of high-impedance qubits. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G68.00004: Quantum simulation in circuit QED: Observation of quantum many-body effects due to zero point fluctuations - II: Experiment Sebastien Leger, Javier Puertas, Karthik Srikanth Bharadwaj, Remy Dassonneville, Jovian Delaforce, Farshad Foroughi, Vladimir Milchakov, Luca Planat, Olivier Buisson, Cécile Naud, Wiebke Guichard, Serge Florens, Izak Snyman, Nicolas Roch Electromagnetic fields possess zero point fluctuations (ZPF) which lead to observable |
Tuesday, March 3, 2020 12:27PM - 12:39PM |
G68.00005: Analog quantum simulation of a Kondo impurity with superconducting circuits Nicholas Grabon, Roman Kuzmin, Nitish Jitendrakumar Mehta, Moshe Goldstein, Vladimir Manucharyan
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Tuesday, March 3, 2020 12:39PM - 12:51PM |
G68.00006: Simulating a Dirac particle with coupled transmon circuits Elisha Svetitsky, Nadav Y Katz The core concept of quantum simulation is the mapping of an inaccessible quantum system onto a controllable one by identifying analogous dynamics. We map the Dirac equation of relativistic quantum mechanics in 3+1 dimensions onto a multi-level superconducting Josephson circuit. Resonant drives determine the particle mass and momentum and the quantum state represents the internal spinor dynamics, which are cast in the language of multi-level quantum optics. The degeneracy of the Dirac spectrum corresponds to a degeneracy of bright/dark states within the system and particle spin and helicity are employed to interpret the multi-level dynamics. We simulate the Schwinger mechanism of electron-positron pair production by introducing an analogous electric field as a doubly degenerate Landau-Zener problem. All proposed measurements can be performed well within typical decoherence times. This work opens a new avenue for experimental study of the Dirac equation and provides a tool for control of complex dynamics in multi-level systems. |
Tuesday, March 3, 2020 12:51PM - 1:03PM |
G68.00007: Quantum Simulation of Hyperbolic Space with Circuit Quantum Electrodynamics: From Graphs to Geometry Igor Boettcher, Przemyslaw Bienias, Ron Belyansky, Alicia Kollar, Alexey V Gorshkov We give a quantum field theoretic perspective on recent breakthrough experiments in circuit quantum electrodynamics, where hyperbolic lattices are realized with superconducting resonators and photons are tricked into believing that space is hyperbolic. We show how these finite lattice geometries can be mapped onto quantum field theories in continuous negatively curved space. We use this as a computational tool to quantitatively reproduce ground state energy, spectral gap, and correlation functions of the noninteracting lattice system by means of analytic formulas on the Poincare disk, and show how conformal symmetry emerges for large lattices. I will discuss how interaction effects can be induced by coupling qubits to the hyperbolic lattice. This sets the stage for studying interactions and disorder on hyperbolic graphs, and to resolve fundamental open problems at the interface of interacting many-body systems, quantum field theory in curved space, and quantum gravity using tabletop experiments. |
Tuesday, March 3, 2020 1:03PM - 1:15PM |
G68.00008: Demonstration of programmable quantum simulations of lattice models using a superconducting parametric cavity Jamal Busnaina, Jimmy Shih-Chun Hung, M.V. Moghaddam, Chung Wai Sandbo Chang, A.M. Vadiraj, Hadiseh Alaeian, Enrique Rico, C.M. Wilson There has been a growing interest in realizing quantum simulators for important physical systems where perturbative methods are ineffective. The scalability and flexibility of circuit quantum electrodynamics (cQED) make it a promising platform for implementing various types of simulators, including lattice models of strongly-coupled field theories. With this in mind, we use a multimode superconducting parametric cavity to create programmable lattices of bosonic modes by parametrically pumping at mode-difference frequencies. The choice of pump frequencies allows changing the graph of the lattice in situ. Further, the resulting hopping terms induced between the modes can be made complex by controlling the relative phases of the parametric drives. This enables us to study a wide variety of interesting lattice models. For instance, controlling the total loop phase in closed plaquettes allows us to simulate the motion of particles in a static gauge field, including producing nonreciprocal transport. The system can also realize models with topological features such as the bosonic Creutz ladder. In this talk, we present experimental results on a variety of different small lattice models. |
Tuesday, March 3, 2020 1:15PM - 1:27PM |
G68.00009: Quantum simulation of a spin chain with superconducting circuits Quentin Ficheux, Aaron Somoroff, Nitish Jitendrakumar Mehta, Roman Kuzmin, Ivar Martin, Maxim G Vavilov, Vladimir Manucharyan An Ising chain is one of the simplest many-body systems to exhibit a quantum phase transition. In the presence of a transverse field and disorder, this model produces a rich variety of non integrable ground states giving rise to exotic phase transitions including many body localization and Anderson localization. |
Tuesday, March 3, 2020 1:27PM - 1:39PM |
G68.00010: Growth and preservation of entanglement in a many-body localized system Ben Chiaro, Brooks Foxen, Matthew McEwen, John M Martinis
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Tuesday, March 3, 2020 1:39PM - 1:51PM |
G68.00011: Approximating finite-temperature dynamic correlation functions on quantum computers Jeffrey Cohn, Khadijeh Najafi, Barbara Jones, James Freericks Dynamic correlation functions such as single particle Green's functions, linear response functions, or dynamical susceptibilities serve as a foundational tool kit for studying strongly correlated quantum systems. Ideally, a quantum computer will be able to extract these functions for systems sizes that are intractable on classical computers. When it comes to studying these functions at finite temperature the main bottleneck comes from the resource overhead and circuit complexities required in preparing each Gibbs sample. We present a framework aimed at alleviating this bottleneck by optimizing a series of approximations. Specifically, we sample from a series of time averaged embedded clusters initially in their respective local Gibbs states. After extracting each approximate dynamic correlation function we employ Richardson extrapolation where the error expanded in the series is determined by the total number of sub-clusters used in each approximation. We obtain higher order estimates for each distinct path of approximations. We can optimize even further by weighting each distinct path by how closely each path fits the proper fluctuation theorem. We demonstrate this toolbox numerically using exact diagonalization of the Hubbard model on small clusters. |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G68.00012: Band engineering for quantum simulation with superconducting circuits Christie Chiu, Andrew Houck Quantum simulation has been implemented on a variety of experimental platforms such as neutral atoms, ions, quantum dots, and superconducting circuits, each offering unique features. Superconducting circuits can and have been used to realize artificial photonic materials in a wide range of lattice geometries and graph connectivities, due to the flexibility of on-chip fabrication. In addition, photon-photon interactions are highly tunable using nonlinearities such as superconducting qubits, leveraging the vast toolkit developed for quantum computation. Here I report on recent progress towards engineering flat bands for studies of strongly correlated many-body physics. |
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G68.00013: Propagation and Localization of Collective Excitations on a 24-Qubit Superconducting Processor Yangsen Ye Superconducting circuits have emerged as a powerful platform of quantum simulation, especially for emulating the dynamics of quantum many-body systems. Here we construct a Bose-Hubbard ladder with a ladder array of 20 qubits. We then use pairs of controllable qubits to study the dynamics of the ladder model. We investigate theoretically and demonstrate experimentally the dynamics of single- and double-excitation states with distinct behaviors. We observe linear propagation of photons in the single-excitation case. The double-excitation state, initially placed at the edge, localizes; while placed in the bulk, it splits into two single-excitation modes. Our work paves the way to simulation of exotic logic particles by subtly encoding physical qubits and exploration of rich physics by superconducting circuits. |
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