Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F40: Noisy Intermediate Scale Quantum Computers IVFocus Recordings Available

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Sponsoring Units: DQI DCOMP Chair: Crystal Noel, Duke Room: McCormick Place W196B 
Tuesday, March 15, 2022 8:00AM  8:12AM 
F40.00001: Observation of TimeCrystalline Eigenstate Order on a Quantum Processor Xiao Mi, Vedika Khemani, Pedram Roushan, Matteo Ippoliti, Kostyantyn Kechedzhi, Shivaji Sondhi, Roderich Moessner, Vadim Smelyanskiy, Yu Chen, Chris Quintana, Zijun Chen, Amy Greene, Jonathan Gross Quantum processors of today are already capable of surpassing classical supercomputers on certain specialized tasks. A current milestone for the quantum information science community is the fulfilment of quantum computational advantage on a practical problem of interest. Studying manybody phases of matter offers unique opportunities toward this coveted goal since many outstanding questions remain surrounding the critical behaviors of quantum phases. Here we report on the experimental observation of a nonequilibrium phase of matter, the discrete time crystal (DTC). A DTC breaks timetranslational symmetry and displays spatiotemporal quantum order in all of its eigenstates, a feature dubbed “eigenstate order”. We implement Floquet dynamics on a 1D chain of 20 superconducting qubits [1]. Engineered disorders in the twoqubit couplings allow manybody localization (MBL) to occur despite strong external drive, thereby stabilizing the nonequilibrium phase [2]. We carefully validate the phase structure of the DTC by probing the average response of all eigenstates belonging to the Floquet unitary. Using a suitable choice of order parameter, we further identify the location of the MBLergodicity crossover via experimentally observed finitesize effects. These results open a direct path to studying quantum phase transitions and critical phenomena on NISQ quantum processors. 
Tuesday, March 15, 2022 8:12AM  8:24AM 
F40.00002: Simulation of an absorbing state nonequilibrium phase transition on a trapped ion quantum computer Eli Chertkov, David Hayes, Michael FossFeig Quantum computers have the potential to perform simulations of many interacting quantum particles more efficiently than classical computers. Open quantum systems, exhibiting dissipation in addition to unitary dynamics, can be difficult to simulate classically and can give rise to rich nonequilibrium behavior. Recently, a class of open systems with fluctuationless absorbing states has been studied numerically and shown to exhibit a nonequilibrium phase transition even in onedimension [1]. Using the highfidelity midcircuit measurement and qubit reuse capabilities of a Honeywell trapped ion quantum computer [2], we simulate an open quantum system with an absorbing state transition. In this talk, we present our experimental study probing the nonequilibrium phase transition in this model. 
Tuesday, March 15, 2022 8:24AM  8:36AM 
F40.00003: Survey of dynamical decoupling sequences on superconducting qubit devices Nic Ezzell, Bibek B Pokharel, Daniel A Lidar Dynamical decoupling (DD) is the judicious placement of control pulses to decouple a quantum system from its environment without the need for feedback. In this work, we survey a fairly comprehensive set of DD sequences across 3 superconducting qubit IBM devices. (1) We start by showing that DD can preserve a quantum state much longer than freely evolving it. (2) Next, we demonstrate that advanced DD sequences can greatly outperform wellknown sequences like CPMG and XY4 when given a small set of additional pulselevel controls available with OpenPulse but not with standard circuit programming. (3) We then show how DD can be used to perform noise spectroscopy. (4) Finally, we connect our theoretical expectations of sequence behavior to actual performance in the context of the device physics such as the use of finite width pulses and noise. Though our work focuses on superconducting devices, our methodology and many of our conclusions are broadly applicable to any NISQ device. 
Tuesday, March 15, 2022 8:36AM  8:48AM 
F40.00004: Variational Trotter compression algorithm for quantum dynamics simulations on noisy intermediatescale quantum computers Peter P Orth, Noah F Berthusen, Thais V Trevisan, Thomas Iadecola Simulating quantum dynamics of interacting manybody systems is one of the primary potential applications of quantum computing, since the growth of entanglement makes such simulations exponentially hard on classical computers. The shallow circuit requirement of current noisy QPUs, however, limits traditional algorithms based on Trotter product formulas to simulations of the early time dynamics, and instead favors the use of variational quantum algorithms. Here, we present and benchmark an algorithm that combines Trotterized state evolution over short times with a variational compression step that uses the state overlap as a cost function. We implement the algorithm on IBM hardware and show quantum dynamics simulation results for a few site Heisenberg spin chain beyond the coherence time of the device. We discuss the impact of sample and gate noise as well as various error mitigation strategies on the performance and scalability of the algorithm, and present results on noisy and noiseless simulators of systems up to six and eleven sites, respectively. 
Tuesday, March 15, 2022 8:48AM  9:00AM 
F40.00005: Simulating stringorder melting in superconducting hardware with optimal control Paul M Kairys, Travis S Humble Utilizing optimal control to achieve quantum simulation is an emerging strategy that combines intrinsic device physics with digital quantum simulation methods. Here we assess this strategy by designing protocols to probe the static and dynamic properties of symmetryprotected topological (SPT) states on superconducting transmon hardware. Specifically, we design methods to study stringorder melting, in which a symmetrybreaking quench is applied to a prepared SPT state, leading to rapid decay in string order. To demonstrate feasibility we map a twosite AKLT Hamiltonian into a transmon device architecture and use numerical simulations to identify optimal controls which model stringorder melting on nearterm quantum hardware. We conclude by discussing additional opportunities to investigate SPT phases using quantum simulation with optimal control. 
Tuesday, March 15, 2022 9:00AM  9:12AM 
F40.00006: Smallworld complex network generation by quantum cellular automata simulated on a digital quantum processor Eric B Jones, Logan E Hillberry, Matthew T Jones, Mina Fasihi, Pedram Roushan, Zhang Jiang, Alan Ho, Charles J Neill, Eric Ostby, Peter Graf, Eliot Kapit, Lincoln D Carr Quantum cellular automata (QCA) evolve qubits in a quantum circuit depending only on the states of their neighborhoods and model how rich physical complexity can emerge from a simple set of underlying dynamical rules. For instance, Goldilocks QCA depending on tradeoff principles exhibit nonequilibrating coherent dynamics and generate complex mutual information networks. The inability of classical computers to simulate large quantum systems is a hindrance to understanding the physics of QCA, but quantum computers offer an ideal simulation platform. Here we demonstrate the first experimental realization of QCA on a digital quantum processor, simulating a onedimensional Goldilocks rule on chains of up to 23 superconducting qubits. Employing lowoverhead calibration and error mitigation techniques, we calculate population dynamics and complex network measures indicating the formation of smallworld mutual information networks. Unlike random states, these networks decohere at fixed circuit depth independent of system size; the largest of which corresponds to 1,056 twoqubit gates. Such computations may open the door to the employment of QCA in applications like the simulation of stronglycorrelated matter or beyondclassical computational demonstrations. 
Tuesday, March 15, 2022 9:12AM  9:48AM 
F40.00007: Efficient Multiphoton Sampling of Molecular Vibronic Spectra on a Superconducting Bosonic Processor Invited Speaker: Robert J Schoelkopf Circuit quantum electrodynamics, in which microwave cavity modes are coupled to “artificial atoms” realized with Josephson junction qubits, has allowed for a variety of investigations in quantum optics and quantum information. In recent years, our team at Yale has focused on a hardware efficient approach, where highQ microwave cavities serve as quantum memories. When dispersively coupled to transmon qubits, complex nonclassical states can be created in these cavities, and operations between cavities can be enacted through parametric driving. For instance, we have recently shown highquality cavitycavity swaps via a beamsplitter or conversion operation, single and twomode squeezing, and engineered cross and selfKerr interactions. Finally, one can perform strong projective measurements of the photon number, the photon parity, or indeed any other binaryvalued operator within the multidimensional Hilbert space. This system therefore has all of capabilities of linear optical systems, but with the addition of deterministic state preparation, measurement, and nonlinear interactions. One way to employ these capabilities is to directly simulate problems which are “naturally” bosonic in nature. In this talk, I will present our results utilizing these capabilities for determining FranckCondon factors in the vibronic spectra of simple molecules [1], in which a microwave cavity can directly emulate the multiple excitations of a vibrational mode. With this programmable simulator, we obtain good agreement with classical calculations for simple molecules, and employ a novel photon number resolving detection that allows efficient sampling. Finally, we can compare this approach to using a traditional qubitbased simulation, which would require eight or more qubits and thousands of gates, illustrating some of the advantages of direct bosonic emulation. 
Tuesday, March 15, 2022 9:48AM  10:00AM 
F40.00008: Efficiency of calculation and robustness of local observables in opensystem dynamics of Ising models Anupam Mitra, Philip D Blocher, Tameem Albash, Akimasa Miyake, Ivan Deutsch In quantum manybody problems, one is often interested in estimating expectation values of local observables associated with order parameters, which are believed to be more robust to decoherence, making them more accessible to noisy intermediate scale quantum (NISQ) simulators. The computational power of NISQ devices remains an open question. Recent work has shown that approximate simulations can be tractable [1], especially in the presence of decoherence [2, 3]. We show that the HilbertSchmidt distance between appropriate marginal states can be used to upper bound the error in estimating expectation values of observables. Focusing on quantum simulation of quench dynamics of Ising spin chains in 1D on a noisy quantum device, we model open quantum system dynamics with a unital Lindblad master equation involving singlespin Lindblad operators. We show that loworder marginals are less sensitive to approximation via truncated tensor network representations and decoherence, suggesting that expectation values of local observables in Ising spin chains are classically tractable and robust against experimental imperfections in NISQ devices. 
Tuesday, March 15, 2022 10:00AM  10:12AM 
F40.00009: Towards Efficient Quantum Spin System Simulations on NISQ Norhan M Eassa, jeffrey cohn, ZOE HOLMES, Barbara A Jones, Lukasz Cincio, Arnab Banerjee, Andrew T Sornborger, Bilal Khalid Quantum spin systems can demonstrate a variety of interesting quantum phenomena, ranging from soliton lattices to quantum spin liquids, with a potential to constitute key elements in various quantum applications. Inelastic scattering experiments, such as using inelastic neutron scattering (INS) and NMR, provide key insights into the dynamics of spins inside quantum magnets. To understand such spin dynamics, we compute the magnetic neutron crosssection on qubitbased hardware extending the prescription laid in Nature Phys. 15, 455 (2019). We have utilized the IBM quantum devices to simulate the time evolution of different Hamiltonians acting on an initial state for spin½ systems, starting from 2spin systems and extending above, and have been able to measure the coefficients of the correlation functions. In order to mitigate the backend noise and to capture longer time dynamics, we use a variational fastforwarding (VFF) ansatz, and compare the results to that of trotterization, as well as compare between direct (ancilla qubitfree circuits) and indirect (circuits including ancilla qubit) measurements. We end with ongoing ideas to expand to larger spin networks to emulate scattering results from INS measurements. 
Tuesday, March 15, 2022 10:12AM  10:24AM 
F40.00010: Determining groundstate phase diagrams on quantum computers via a generalized application of adiabatic state preparation Akhil Francis, Ephrata Zelleke, Ziyue Zhang, Alexander F Kemper, James K Freericks Quantum phase transitions materialize as level crossings in the groundstate energy when the parameters of the Hamiltonian are varied. The resulting groundstate phase diagrams are straightforward to determine by exact diagonalization on classical computers, but are challenging on quantum computers because of the accuracy needed and the near degeneracy of competing states close to the level crossings. In this work, we use a local adiabatic ramp for state preparation to allow us to directly compute groundstate phase diagrams on a quantum computer via time evolution. This methodology is illustrated by examining the ground states of the XY model with a magnetic field in the zdirection in one dimension. We are able to calculate an accurate phase diagram on both two and three site systems using IBM quantum machines. 
Tuesday, March 15, 2022 10:24AM  10:36AM 
F40.00011: Simulating nanoscale NMR problems on a CoDesign quantum computer, part I Mario Ponce Martinez, Manuel García Pérez de Algaba, Hermanni Heimonen, Carlos MunueraJavaloy, Jorge Casanova, Martin Leib, Ines de Vega Nitrogenvacancy (NV) color centers in diamond can be used as quantum sensors in the context of nanoscale nuclear magnetic resonance (NMR) experiments. Certain microwave radiation patterns can drive a selective coupling between NV and nearby nuclei to hyperpolarize the nuclear spins. 
Tuesday, March 15, 2022 10:36AM  10:48AM 
F40.00012: Simulating nanoscale NMR problems on a CoDesign quantum computer, part II Manuel García Pérez de Algaba, Mario Ponce Martinez, Hermanni Heimonen, Carlos MunueraJavaloy, Jorge Casanova, Martin Leib, Ines de Vega Current quantum devices do not yet allow for implementations of complex quantum algorithms solving practical problems. The objective of CoDesign is to ease this task by optimizing the algorithm and hardware in combination. We apply this approach to a quantum simulation algorithm for a diamond nuclear spin hyperpolarization protocol designed by us as presented in part I. Different qubit topologies are studied in terms of the required number of SWAPs and the gate fidelities required to solve the problem up to a specific precision on NISQ hardware. We show that by choosing a suitable circuit topology we can significantly reduce the gate fidelity requirements. Also, the use of problemspecific hardware tools, such as the quantum circuit refrigerator (QCR), is discussed. 
Tuesday, March 15, 2022 10:48AM  11:00AM 
F40.00013: Noise robustness of quantum approximate optimization against correlated errors. Joris Kattemölle, Guido Burkard The Quantum Approximate Optimization Algorithm (QAOA) has the potential of providing a quantum advantage in largescale optimization problems, as well as in finding the ground state of spin glasses. This algorithm is especially suited for Noisy Intermediate Scale Quantum (NISQ) devices because of its expected noise resilience. In fully errorcorrected quantum computers, error correlations are known to lead to increased overhead. The effect of noise correlations on NISQ algorithms such as QAOA, however, remained largely unknown. In this work, we study by numerical simulation the causes and effects of the noise correlations on the performance of QAOA. We find evidence that the approximation ratio obtained by QAOA improves polynomially as the strength of the correlations is increased. This shows that, as opposed to fully errorcorrected quantum computers, noise correlations can improve the performance of NISQ algorithms such as QAOA. This opens the way towards tailoring NISQ algorithms to leverage noise correlations, thereby boosting their noise resilience. 
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