Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X10: Quantum Characterization, Verification, and ValidationLive
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Chair: Ben Lawrie, ORNL |
Friday, June 4, 2021 8:00AM - 8:12AM Live |
X10.00001: Temporal Quantum Correlations in Superconducting-Qubit Systems Hao-Cheng Weng, Chen-Yeh Wei, Huan-Yu Ku, Shin-Liang Chen, Yueh-Nan Chen, Chih-Sung Chuu Nonlocality has long been studied through quantum correlations between spatially separated measurements on the bipartite systems. Its temporal analogue, in which measurements on a quantum state are separated in time, examines the quantum correlations violating the macrorealism, for example the Leggett-Garg inequality. In this work, we investigate the temporal quantum correlations of a superconducting qubit undergoing stochastic noise through the studies of the nonmacrorealism, temporal steering, and temporal inseparability. Decoherence of different forms can be observed with the quantum correlations, and unique sudden-death and revival of temporal correlations under non-Markovianity can also be identified and quantified. Our work shows that the temporal quantum correlations can provide a benchmark for the decoherence in superconducting quantum devices. |
Friday, June 4, 2021 8:12AM - 8:24AM Live |
X10.00002: Emergent Randomness from Many-Body Quantum Chaos Adam L Shaw, Joonhee Choi, Ivaylo S Madjarov, Xin Xie, Jacob P Covey, Jordan Cotler, Daniel Mark, Hsin-Yuan Huang, Anant Kale, Hannes Pichler, Fernando Brandao, Soonwon Choi, Manuel Endres In this talk we introduce a new method for generating random quantum state ensembles in an experimentally practical manner, and observe signatures of these ensembles using a Rydberg quantum simulator. Concretely, we find that universal and highly random state ensembles are encoded in a wavefunction resulting from chaotic quantum many-body dynamics; these ensembles can be uncovered when the correlations between complementary subsystems are properly captured. Our results offer both a new approach for studying many-body chaos and quantum thermalization, and an easily-implementable method for sampling quantum states randomly over the Hilbert space; the latter enables quantum platforms with limited spatiotemporal control to realize a variety of previously inaccessible applications, such as device benchmarking. |
Friday, June 4, 2021 8:24AM - 8:36AM Live |
X10.00003: Quantum many-body inspired generative models Sona Najafi, Mikhail Lukin, Susanne F Yelin Generative models which learn the underlying probability distribution of the unlabeled data and generate new samples accordingly have become one of the cornerstones of probabilistic machine learning. Inspired by the probabilistic nature of quantum mechanics, we employ a generative model, known as the" Born machine" which uses quantum state representation and learns the joint probabilities over such quantum degrees of freedom. Due to many competing degrees of freedom, quantum many-body systems have known to exhibit exotic phases such as many-body localized states (MBL) which manifest peculiar properties in terms of coherence and long-time memories. In this work, we first introduce the MBL-Born machine as a powerful ansatz for the Born machine, and then we investigate the expressibility and trainability of the machine. We show that the MBL-Born machine is able to learn various classical and quantum data set such as MNIST and different phases of quantum many body states. |
Friday, June 4, 2021 8:36AM - 8:48AM Live |
X10.00004: Quantum Device Benchmarking from Many-Body Quantum Chaos Joonhee Choi, Adam L Shaw, Ivaylo S Madjarov, Xin Xie, Jacob P Covey, Jordan Cotler, Daniel Mark, Hsin-Yuan Huang, Anant Kale, Hannes Pichler, Fernando Brandão, Soonwon Choi, Manuel Endres Here we present a simple and efficient benchmarking protocol to estimate the many-body fidelity between a target state and the actual state obtained from experimental evolution. Our protocol relies only on time evolution of a quantum system undergoing chaotic dynamics, followed by projective measurements in a fixed local basis without any local control; this is in stark contrast to many existing methods which require fine-tuned spatiotemporal control and substantial experimental resources that scale exponentially with system size. Fundamentally, this simplification stems from a universal phenomenon in many-body quantum chaos: the emergence of universal random statistics in a local region. We demonstrate our benchmarking protocol numerically for random unitary circuits, and experimentally using a Rydberg quantum simulator. |
Friday, June 4, 2021 8:48AM - 9:00AM Live |
X10.00005: Benchmarking mid-circuit measurement and reset Charles H Baldwin, John Gaebler, Juan Pino, Joan Dreiling, Caroline Figgatt, Steven A Moses Mid-circuit measurement and reset is a crucial primitive in quantum error correction but so far there have been few demonstrations and even fewer methods proposed to benchmark performance. We present a new method, based on randomized benchmarking, to estimate performance of mid-circuit measurement and reset that quantifies the effects on the target qubit as well as any crosstalk errors on nearby qubits. We use the method to benchmark mid-circuit measurement and reset on Honeywell System Model H0 and find measurement and reset on the target qubit have high fidelity with low crosstalk errors on nearby qubits thanks to a new micromotion hiding technique, which is presented independently. |
Friday, June 4, 2021 9:00AM - 9:12AM Live |
X10.00006: Efficient Cross-Platform Comparison of Quantum States via Randomized Measurement Ze-Pei Cian, Daiwei Zhu, Crystal Noel, Andrew Risinger, Debopriyo Biswas, Yingyue Zhu, Qingfeng Wang, Yunseong Nam, Mohammad Hafezi, Marko Cetina, Norbert M Linke, Christopher R Monroe One of the many additional complexities that quantum computers pose over classical computers is verifying and comparing quantum states. One way to verify quantum states is to reconstruct the entire density matrix, which requires measurements exponentially growing with the number of qubits. Recent work has proposed approaches based on randomized measurement to reduce the number of measurements needed to compare quantum states (although still exponential), whether across different systems or across time. We discuss recent results applying this technique to a variety of ion trap and superconductor quantum computing systems, and contrast various states produced by different systems. |
Friday, June 4, 2021 9:12AM - 9:24AM Live |
X10.00007: Nonlinear Bell inequality for macroscopic measurements Adam Bene Watts The correspondence principle suggests that quantum systems grow classical when large. Classical systems cannot violate Bell inequalities. Yet agents given substantial control can violate Bell inequalities proven for large-scale systems. We consider agents who have little control, implementing only general operations suited to macroscopic experimentalists: preparing small-scale entanglement and measuring macroscopic properties while suffering from noise. That experimentalists so restricted can violate a Bell inequality appears unlikely, in light of earlier literature. Yet we prove a Bell inequality that such an agent can violate, even if experimental errors have variances that scale as the system size. A violation implies nonclassicality, given limitations on particles' interactions. A product of singlets violates the inequality; experimental tests are feasible for photons, solid-state systems, atoms, and trapped ions. Consistently with known results, violations of our Bell inequality cannot disprove local hidden-variables theories. By rejecting the disproof goal, we show, one can certify nonclassical correlations under reasonable experimental assumptions. |
Friday, June 4, 2021 9:24AM - 9:36AM Live |
X10.00008: Characterization of Fast Ion Transport via Position-Dependent Optical Deshelving Craig R Clark Ion transport is an essential operation within some models of quantum computing, where fast ion transport with minimal motional excitation is necessary for efficient, high-fidelity operations. We demonstrate fast linear transport of Ca+ in a surface-electrode ion trap, measuring average ion velocities up to 219 m/s over a distance of 120 µm by characterizing the ion’s trajectory via a position-dependent optical deshelving technique. Here we prepare the ion in the D5/2 level before transport and then partially repump it to S1/2 via a short (100 ns) 854 nm laser pulse at a later time. The Gaussian intensity profile of the laser beam leads to a position-dependent repump probability which we measure and invert to determine the ion’s position at a given instant. We also characterize the axial normal mode excitation using a Fast Fourier Transform analysis of the blue sideband Rabi spectroscopy to obtain the thermal and coherently excited portions of the ion’s motional state. We remove the coherently excited portion by applying a resonant radiofrequency pulse with appropriate amplitude, frequency, and phase to achieve a final axial mode occupation n<1. This work was done in collaboration with Los Alamos National Laboratory. |
Friday, June 4, 2021 9:36AM - 9:48AM Live |
X10.00009: Benchmarking the Honeywell H1 QCCD Trapped-Ion Quantum Computer Justin G Bohnet, Aaron Hankin, Daniel Gresh, John Gaebler, David Francois, Kenneth Lee, Charlie Baldwin, Karl H Mayer, David Hayes, Russell Stutz We have developed a 10 qubit quantum computer, based on the quantum charge coupled device (QCCD) architecture, using a cryogenic, 2D surface-electrode Honeywell ion trap. The QCCD is a scalable architecture for universal quantum computation using trapped ions as qubits. The device controls multiple mixed-species ion pairs of Yb+ and Ba+ to serve as a qubit and sympathetic coolant respectively. Full connectivity is achieved by transporting qubits between custom-purpose trap zones, enabling high fidelity, parallel quantum operations with minimal crosstalk. We will report on recent techniques used to benchmark our device, utilizing algorithms that characterize gate and mid-circuit measurement fidelity. We analyze how benchmarks focused on isolating single operations predict performance in holistic benchmarks, such as quantum volume, and in practical circuits. Our results demonstrate that the low error rates achievable in small ion crystals can be successfully integrated with a QCCD trap design and ion transport. |
Friday, June 4, 2021 9:48AM - 10:00AM Live |
X10.00010: Characterization and Control of Large-Scale Ion-Trap Quantum Computers Andrew Risinger, Daniel Lobser, Alan Bell, Crystal Noel, Laird Egan, Daiwei Zhu, Debopriyo Biswas, Marko Cetina, Christopher R Monroe Performing Quantum Characterization, Verification, and Validation (QCVV) on large-scale ion-trap quantum computers is a challenging task because it requires a control system capable of quickly compiling and running large numbers of quantum circuits with minimal dead time. One limiting factor is the control hardware used for driving quantum gates: circuit waveforms for Arbitrary Waveform Generators (AWGs) are slow to compute and program, and Direct Digital Synthesizers (DDSs) are slow to modulate. These shortcomings can be addressed by parametric waveform generation, addressing the shortcomings of DDSs and AWGs, enabled by integration of RF output with an FPGA via a Xilinx RFSoC. We present integration of an RF System on a Chip (RFSoC) FPGA into our ion-trap quantum computer. We also present progress on using this new waveform generator to perform QCVV on a system with more than 10 qubits. |
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