Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D40: Noisy Intermediate Scale Quantum Computers IIIFocus Recordings Available
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Sponsoring Units: DQI DCOMP Chair: William Huggins, Google Room: McCormick Place W-196B |
Monday, March 14, 2022 3:00PM - 3:12PM |
D40.00001: Locality and entanglement properties across the many-body spectrum in a 4x4 array of superconducting qubits (part 1): Theory Yariv Yanay, Amir H Karamlou, Agustin Di Paolo, Patrick M Harrington, Sarah E Muschinske, Jochen Braumuller, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Mollie E Schwartz, Jeffrey A Grover, Simon Gustavsson, Charles Tahan, William D Oliver The spectrum of a strongly interacting system can display properties of localization and entanglement that cannot be understood in terms of single-particle physics. In this work, we use a two-dimensional 4x4 array of superconducting transmon qubits as a quantum simulator to explore these properties in the strongly-interacting hard-core Bose-Hubbard model. Using the simultaneous control and readout capability of our system, we generate non-thermal, coherent excited states in the lattice, and probe its many-body spectrum and properties to observe the transition between local and delocalized many-body modes. In this part of the talk we discuss the theoretical background and experimental concept. |
Monday, March 14, 2022 3:12PM - 3:24PM |
D40.00002: Locality and entanglement properties across the many-body spectrum in a 4x4 array of superconducting qubits (part 2): Experiments Amir H Karamlou, Yariv Yanay, Sarah E Muschinske, Agustin Di Paolo, Patrick M Harrington, Jochen Braumueller, David K Kim, Alexander Melville, Bethany M Niedzielski, Jonilyn L Yoder, Mollie E Schwartz, Jeffrey A Grover, Simon Gustavsson, Charles Tahan, William D Oliver The spectrum of a strongly interacting system can display properties of localization and entanglement that cannot be understood in terms of single-particle physics. In this work, we use a two-dimensional 4x4 array of superconducting transmon qubits as a quantum simulator to explore these properties in the strongly-interacting hard-core Bose-Hubbard model. Using the simultaneous control and readout capability of our system, we generate non-thermal, coherent excited states in the lattice, and probe its many-body spectrum and properties to observe the transition between local and delocalized many-body modes. In this part of the talk, we discuss the experimental results obtained from our device. |
Monday, March 14, 2022 3:24PM - 3:36PM |
D40.00003: Investigation of Measurement-Induced Entanglement Transitions on a Superconducting Quantum Computer Jin Ming Koh, Shi-Ning Sun, Mario Motta, Austin J Minnich A many-qubit system subject to random unitary evolution with interspersed projective measurements can exhibit distinct entangling and disentangling phases, separated by a critical measurement rate. However, these systems have been studied primarily using classical calculations with Clifford circuits. Here, we report a study of measurement-induced entanglement transitions using transmon-based IBM Quantum devices, which support mid-circuit measurements and sub-microsecond readout times. We observe a crossover in the entanglement entropy between an entangling phase, characterized by volume-law scaling, and a disentangling phase, characterized by area-law scaling. We further investigate crossovers induced by weak measurements of varying strength, using ancillary qubits. Lastly, we estimate the critical measurement rate and critical exponents characterizing the transition. Our work indicates that near-term quantum computers can be useful in exploring quantum phases and dynamical behaviour under monitoring protocols. |
Monday, March 14, 2022 3:36PM - 3:48PM |
D40.00004: Observation of dynamical phase transitions in a superconducting quantum processor implementing five stabilizer terms Shavindra P Premaratne, Albert T Schmitz, Miguel Moreira, Leonardo DiCarlo, Anne Y Matsuura The dynamical phase transition (DPT) [1] in many-body systems is of recent interest due to the ability to engineer these non-equilibrium quantum phases in the laboratory. DPTs are typically defined as non-analytic behavior in the dynamical free energy. They have also been shown to represent error correction properties when applied to stabilizer codes [2]. Here, we report on results from the d=2 toric code (also known as a surface code) when including 5 stabilizer terms, and executed on the QuTech Quantum Inspire superconducting quantum processor. We observe good agreement between experiment and theory when accounting for experimentally calibrated error sources. |
Monday, March 14, 2022 3:48PM - 4:00PM |
D40.00005: Realization of symmetry-protected topological phases in a spin-1/2 chain with next-nearest neighbor interactions on a superconducting quantum processor Adrian Tan, Shi-Ning Sun, Ruslan Tazhigulov, Garnet Chan, Austin J Minnich The realization of novel phases of matter on quantum simulators is a topic of intense interest. Digital quantum computers offer a route to prepare topological phases with interactions that do not naturally arise in analog quantum simulators. Here, we report the realization of symmetry-protected topological (SPT) phases of a spin-1/2 Hamiltonian with next-nearest-neighbor hopping on up to 11 qubits on a programmable superconducting quantum processor. We observe clear signatures of the two distinct SPT phases such as excitations localized to specific edges and non-zero string order parameters. Our work advances ongoing efforts to realize novel states of matter with exotic interactions on digital near-term quantum computers. |
Monday, March 14, 2022 4:00PM - 4:12PM |
D40.00006: A dynamic quantum algorithm for the stochastic Schrödinger equation on near-term hardware using selective qubit reset Hirsh Kamakari, Mario Motta, Austin J Minnich Open quantum systems are of wide interest owing to their ubiquity and rich physical phenomena; however, the features that make the systems interesting also render their simulation challenging on near-term quantum hardware. Various algorithms for simulating open quantum systems on quantum hardware have been proposed. Except for variational algorithms, all previous proposals either require ancilla qubits to implement the non-unitary evolution or exploit hardware-specific noise channels. Here we propose an ancilla-free, non-variational dynamic quantum algorithm for simulating the jump stochastic Schrödinger equation (SSE) on near-term quantum hardware. In the most common unravelling, time evolution is generated from the SSE through a series of non-unitary continuous-time evolutions as well as probabilistic "quantum jumps," or discontinuous changes in the quantum state associated with Lindblad operators. The continuous non-unitary evolution can be implemented by the quantum imaginary time evolution algorithm. We implement the quantum jumps using mid-circuit measurements and sub-microsecond readout capability recently introduced on transmon-based IBM Quantum devices. Our approach enables the simulation of open quantum systems without variational optimization or any ancilla qubits. |
Monday, March 14, 2022 4:12PM - 4:48PM |
D40.00007: Observing measurement-induced quantum phases in a trapped-ion quantum computer Invited Speaker: Crystal Noel Many-body open quantum systems balance internal dynamics against decoherence from interactions with an environment. Here, we explore this balance via random quantum circuits implemented on a trapped-ion quantum computer, where the system evolution is represented by unitary gates with interspersed projective measurements. As the measurement rate is varied, a purification phase transition is predicted to emerge at a critical point akin to a fault-tolerent threshold. We probe the "pure'' phase, where the system is rapidly projected to a deterministic state conditioned on the measurement outcomes, and the "mixed'' or "coding'' phase, where the initial state becomes partially encoded into a quantum error correcting codespace. We find evidence of the two phases and show numerically that, with modest system scaling, critical properties of the transition emerge. |
Monday, March 14, 2022 4:48PM - 5:00PM |
D40.00008: Benchmarking VQE for the square-octagon-lattice Kitaev model Andy C. Y. Li, M. Sohaib Alam, Thomas Iadecola, Ammar Jahin, Doga Kurkcuoglu, Richard Li, Peter P Orth, A. Baris Ozguler, Gabriel Perdue, Norm M Tubman The variational quantum eigensolver (VQE) is a promising apporoach to find eigenstates and eigenenergies on NISQ devices. In this presentation, we consider the Kitaev spin model with a square-octagon lattice geometry that matches the connectivity map of Rigetti's QPUs. The hardware-native geometry allows the possibility of efficiently exploring the spin model's rich phase diagram with the VQE approach. We will illustrate the advantage of a mixed optimization approach using the Hamiltonian variational ansatz (HVA) by benchmarking several choices of variational ansatzes and classical optimizers. We will also demonstrate the implementation of a proof-of-principle HVA circuit on the Rigetti's Aspen-9 QPU with appropriate error mitigation techniques. |
Monday, March 14, 2022 5:00PM - 5:12PM |
D40.00009: Preparing the AKLT state on a quantum computer Kevin C Smith, Eleanor Crane, Nathan Wiebe, Steven M Girvin The preparation and validation of physically interesting and useful quantum states and phases remains an important problem, particularly on modern NISQ devices. A prototypical example is the AKLT model, describing a one-dimensional spin-1 chain with generalized nearest-neighbor, Heisenberg-like interactions. It provides an intuitive realization of a novel, symmetry-protected topological phase displaying fractionalized excitations at the edges, a finite energy gap in the bulk, and a hidden antiferromagnetic ordering. In addition to these exotic properties, the AKLT ground state holds particular promise as a resource for measurement-based quantum computing and other quantum information processing tasks. |
Monday, March 14, 2022 5:12PM - 5:24PM |
D40.00010: Trotter errors from dynamical structural instabilities of Floquet maps in quantum simulation Karthik Chinni, Manuel H Muñoz-Arias, Ivan H Deutsch, Pablo M Poggi We study the behavior of errors in the quantum simulation of spin systems with long-range multi-body interactions resulting from the Trotter-Suzuki decomposition of the time-evolution operator. We identify a regime where the Floquet operator underlying the Trotter decomposition undergoes sharp changes even for small variations in the simulation step size. This results in a time evolution operator that is very different from the dynamics generated by the targeted Hamiltonian, which leads to a proliferation of errors in the quantum simulation. We characterize these regions of sharp change in the Floquet operator, referred to as structural instability regions, in ??-spin models and analytically predict their occurrence based on unitary perturbation theory. We further show that the effective Hamiltonian associated with the Trotter decomposition of the time-evolution operator, when the Trotter-step size is chosen to be in the structural instability region, is very different from the target Hamiltonian, which explains the large errors that can occur in the simulation in the regions of instability. These results have implications for the reliability of near-term gate-based quantum simulators and reveal an interplay between errors and the physical properties of the system being simulated. |
Monday, March 14, 2022 5:24PM - 5:36PM |
D40.00011: Scaling Quantum Approximate Optimization on Near-term Hardware Phillip C Lotshaw, Thien Nguyen, Anthony Santana, Alexander J McCaskey, Rebekah Herrman, James Ostrowski, George Siopsis, Travis S Humble The quantum approximate optimization algorithm (QAOA) is as an approach for near-term quantum computers to potentially demonstrate computational advantage in solving combinatorial optimization problems. However, the viability of the QAOA depends on how its performance and resource requirements scale with problem size and complexity for realistic hardware implementations. Here, we quantify the expected resource requirements by designing optimized circuits for hardware architectures with varying levels of connectivity. Assuming noisy gate operations, we estimate the number of measurements needed to sample the output of the idealized QAOA circuit with high probability. We show the number of measurements, and hence total time to solution, grows exponentially in problem size and problem graph degree as well as depth of the QAOA ansatz, gate infidelities, and inverse hardware graph degree. |
Monday, March 14, 2022 5:36PM - 5:48PM |
D40.00012: Entanglement Phase Transition with Spin Glass Criticality Jeremy Côté, Stefanos Kourtis We define an ensemble of random Clifford quantum circuits whose output state undergoes an entanglement phase transition between two volume-law phases as a function of measurement rate. Our setup provides an exact map between the entanglement entropy of the quantum state and the ground-state entropy of a spin glass model. We identify the entanglement phases using an order parameter that is accessible on a quantum chip. We extract the critical exponents, which reveal spin glass criticality. Our work establishes an exact statistical mechanics theory of an entanglement phase transition. |
Monday, March 14, 2022 5:48PM - 6:00PM |
D40.00013: Optimizing ansatz design in QAOA for Max-Cut Debasmita Bhoumik, Ritajit Majumdar A QAOA finds good approximate solutions to a combinatorial optimization problem. For a graph G=(V, E), |V|=n, |E|=m, a depth p QAOA for Max-Cut requires 2mp CNOT gates. CNOT being 100x more error-prone than single-qubit gates, we propose two hardware-independent methods to reduce the number of CNOT gates in the first iteration of a QAOA circuit for Max-Cut while retaining functional equivalence. First, we utilize Edge Coloring of the graph to minimize the depth and eliminate at most n/2 CNOT gates. Next, we employ Depth First Search (DFS) on the input graph to eliminate n-1 CNOT gates, but the depth of the circuit increases moderately. We derive analytically the criteria for which the reduction in CNOT gates overshadows this increase in depth, leading to an overall lower error probability. All existing IBM Quantum Hardware satisfy this criterion. Finally, we propose an O(\Delta.n^2) greedy algorithm, \Delta being the maximum degree of the graph, that finds a spanning tree of lower height, thus reducing the overall depth of the circuit while retaining the elimination of n-1 CNOT gates. We show that this algorithm achieves ~ 84.8% reduction in depth from the DFS method. Probable methods to scale this for higher p and for specific hardware topologies are under study. |
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