Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F32: Noisy Intermediate Scale Quantum Computers IFocus Live
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Sponsoring Units: DQI DCOMP Chair: David Gosset, University of Waterloo |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F32.00001: The effective central charge of the measurement induced phase transition Aidan Zabalo, Michael Gullans, Justin Wilson, Romain Vasseur, Andreas W Ludwig, Sarang Gopalakrishnan, Jed Pixley, David A Huse Recently, there has been a growing interest in understanding the measurement driven entanglement transition in a variety of random circuit models. Two models that have received a significant amount of attention are the random Haar circuit and the stabilizer circuit. These two models lie in different regimes of computational complexity with the stabilizer circuit being able to be simulated efficiently on a classical computer and the Haar circuit requiring the details of the full Hilbert space. Surprisingly, both of these models seem to share many of the same critical properties with each other and with percolation suggesting they might belong to the same universality class. In this talk, we will introduce a method to calculate the effective central charge of the logarithmic conformal field theory at the critical point. What we find is clear evidence that separates the two circuit models and percolation into three distinct universality classes. This approach is extended to compute the leading Lyapunov exponents of a transfer matrix composed of unitary gates and projective measurements that we use to calculate the scaling dimensions of additional operators in the field theory at the transition. |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F32.00002: Quantum cellular automata part I: Entanglement, physical complexity, and Goldilocks rules Logan Hillberry, Matthew Jones, David L Vargas, Patrick J Rall, Nicole Yunger Halpern, Ning Bao, Simone Notarnicola, Simone Montangero, Lincoln D Carr Cellular automata are interacting classical bits that display diverse behaviors, from fractals to random-number generators to Turing-complete computation. We discover that quantum cellular automata (QCA) can exhibit complexity in the sense of the complexity science that describes biology, sociology, and economics. Complexity-generating QCA, termed Goldilocks rules, exhibit not only rich entanglement, but also persistent entropy fluctuations as well as network structure and dynamics consistent with complexity. In this talk we outline our QCA models and complexity analysis results for 1 dimensional systems. In addition to intuition-building case studies, we examine the effects of initial condition and local interaction phase on the network structure of QCA-generated quantum states, as quantified by scalar functions of the two-point quantum mutual information. In later talks, we will demonstrate that such physical complexity leads to robust correlations, a computational resource, in noisy intermediate scale quantum devices. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F32.00003: Quantum cellular automata part II: Robust complexity under analog and digital evolution in 1- and 2-dimensions Matthew Jones, Logan Hillberry, Eric Jones, Mina Fasihi, Eliot Kapit, Lincoln D Carr, Pedram Roushan, Zhang Jiang Quantum cellular automata are an extension of the classical cellular automata into quantum lattice systems. We consider symmetric, or totalistic, rules in 1- and 2-d quantum analog and digital evolution. We demonstrate the existence of a class of long-lived highly entangled states under noise models consistent with modern noisy intermediate-scale quantum computing fidelity levels. We showcase a robust emergent phenomenon in 1-d called the quantum entangled breather (QEB) which arises from a particular rule. Under certain rule admixtures, the QEB's lifetime exhibits power-law decay in the admixture ratio. The QEB's lifetime also exhibits a threshold-law in its Schmidt rank which indicates the QEB requires a minimum amount of entanglement to persist. We present 2- and 5-qubit gate decompositions of the aforementioned rules, and demonstrate the quantum digital evolution is resilient to depolarizing noise. In all cases, we compute network complexity dynamics based on mutual information and other adjacency matrices optimized for low gate count. We characterize trends in network structure using clustering and disparity fluctuations to quantify the complexity of the quantum states. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F32.00004: Rodeo Algorithm for Quantum Computation Jacob Watkins For closed quantum mechanical systems, the spectrum and eigenvectors of the corresponding Hamiltonian provide a great deal of information concerning dynamic and static properties. In cases where a good initial guess can be supplied, standard quantum phase estimation (QPE) can be used to bring a state closer to a desired eigenstate while simultaneously measuring the corresponding eigenvalue. However, though computationally efficient, standard QPE remains out of reach of current hardware capabilities, in part due to the number of ancilla qubits required to obtain ever higher degrees of precision. In my talk I will present a new approach to the problem of phase estimation, the Rodeo Algorithm, which can be viewed as a generalization of Kitaev’s original algorithm for QPE. Our approach maintains the basic underlying principle of interferometry but allows for a multi-qubit “arena” and stochastically varying phase shifts. I will demonstrate that this algorithm is well suited for NISQ era devices and has good scaling properties in terms of the number of iterations of a simple circuit. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F32.00005: Quantum Computation of Finite-Temperature Static and Dynamical Properties of Spin Systems Using Quantum Imaginary Time Evolution Shi-Ning Sun, Mario Motta, Ruslan Tazhigulov, Adrian Tan, Garnet Chan, Austin Minnich Developing scalable quantum algorithms to study finite-temperature physics of quantum many-body systems has attracted considerable interest due to recent advancements in quantum hardware. However, such algorithms in their present form require resources that exceed the capabilities of current quantum computers except for a limited range of system sizes and observables. Here, we report calculations of finite-temperature properties including energy, static and dynamical correlation functions, and excitation spectra of spin systems with up to four sites on five-qubit IBM Quantum devices. These calculations are performed using the quantum imaginary time evolution (QITE) algorithm and made possible by several algorithmic improvements, including a method to exploit symmetries that reduces the quantum resources required by QITE, circuit optimization procedures to reduce circuit depth, and error mitigation techniques to improve the quality of raw hardware data. Our work demonstrates that the ansatz-independent QITE algorithm is capable of computing diverse finite-temperature observables on near-term quantum devices. |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F32.00006: Quantum Computer Measurements of Phase Shifts Using Wavepacket Edge Time Delays Erik Gustafson, Yingyue Zhu, Patrick Dreher, Norbert M Linke, Yannick Meurice We present a method to extract the phase shifts using a wavepacket edge time delay resulting from a comparison of the real time evolution with and without a potential interaction. This calculation is tested on a quantum computer using real-time simulation of a transverse Ising model in one spatial dimension. Using a 4 site system a wavepacket was constructed to have a localization that simulates a distinct scattering event in space both inside and outside a potential. A time evolution operator describing the progression of the system was constructed and transmission and reflection coefficients were calculated based on the identified quantum Fourier transformed momentum states. A detailed analysis of the of the phase shift calculations for both the IBM Q machines and data from a University of Maryland ion trap quantum computer show the platform independence of the methodology. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F32.00007: Qubit-efficient entanglement spectroscopy using qubit resets Yigit Subasi, Justin Yirka The utility of NISQ devices can be increased by algorithms that fit larger problem sizes on smaller devices. In this talk I will describe qubit-efficient quantum algorithms for entanglement spectroscopy that exploit the ability to measure and reinitialize subsets of qubits in the course of the computation. These algorithms compute the trace of the n-th power of the density operator of a quantum system, i.e. Tr[ρn ]. They use fewer qubits (independent of n) than any previous efficient algorithm while achieving similar performance in the presence of noise. I will introduce the notion of effective circuit depth as a generalization of standard circuit depth suitable for circuits with qubit resets. This tool helps explain the noise-resilience of our qubit-efficient algorithms and should aid in designing future algorithms. Finally, I will report results of experiments on the Honeywell System Model H0, estimating Tr[ρn ] for larger n than would have been possible with previous algorithms. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F32.00008: Quantum advantage for computations with limited space Dmitri Maslov, Jin-Sung Kim, Sergey Bravyi, Theodore James Yoder, Sarah Sheldon Quantum computations have the potential to solve classically intractable problems. In this work, we theoretically prove and experimentally verify a new type of quantum advantage, where computational space is treated as a limited resource. We show that when the computational space is restricted to a single (qu)bit, in theory, a quantum computer outperforms the best classical computer over arbitrary number of input bits greater or equal than 3, and validate the advantage using 3-, 4-, 5-, and 6-input Boolean functions. We implement these experiments over a subset of qubits on ibmq_berlin, a 27-qubit quantum processor, and calibrate custom 2-qubit gates to execute the circuits efficiently. In each case, we demonstrate the algorithmic success probability (ASP) of our quantum computation in excess of the best possible classical ASP, confirming that our quantum experiment reaches beyond the classical means. |
Tuesday, March 16, 2021 1:06PM - 1:42PM Live |
F32.00009: The power of noisy random quantum circuits Invited Speaker: Bill Fefferman In recent years, random quantum circuits have played a central role in the theory of quantum computation. Much of this prominence is due to the recent “quantum supremacy” experiment, which implemented random quantum circuits acting on 53 superconducting qubits. While random quantum circuits enjoy certain advantages that make them ideal for implementation by near-term quantum experiments, it is unclear a priori why they should be difficult to simulate classically. While we know several examples of quantum algorithms which attain exponential speedups over classical computation, they all seem to rely on highly structured circuits (such as quantum Fourier transforms) which are far from typical. Why then should we expect a generic quantum circuit to realize a large computational advantage? |
Tuesday, March 16, 2021 1:42PM - 1:54PM Live |
F32.00010: Quantum error mitigation for fault-tolerant quantum computing Yasunari Suzuki, Suguru Endo, Yuuki Tokunaga Fault-tolerant quantum computing (FTQC) implements universal quantum computing while suppressing physical errors via quantum error correction. Although the effective error rate decreases exponentially with the code distance, it is expected that the number of available physical qubits is restricted even after FTQC is realized in some form. Meanwhile, quantum error mitigation (QEM) was recently introduced for suppressing errors in Noisy Intermediate-Scale Quantum (NISQ) devices for improving computation accuracy of near-term quantum algorithms with its overhead being a greater number of samples. In this work, we show QEM can compensate dominant errors in FTQC without increasing the number of qubits. This scheme will dramatically alleviate required overheads of FTQC for achieving a high-accuracy quantum computing. |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F32.00011: Noisy quantum simulators: theory of random perturbations and characterization of robust observables Pablo Poggi, Nathan Lysne, Kevin Kuper, Ivan Deutsch, Poul Sterndorff Jessen Quantum simulators are widely seen as one of the most promising near-term applications of quantum technologies. However, it remains unclear to what extent a noisy device can output reliable results in the presence of unavoidable imperfections. Here, we study the effect of weak random perturbations of various kinds in the performance of a dynamical quantum simulator and establish a framework that links the robustness of the resulting expectation values to the spectral properties of the output observable. These properties, in turn, can be associated with the macroscopic or microscopic character of the observable. We then show that, under general assumptions and on average over all states, imperfect simulators are able to reproduce the dynamics of macroscopic observables accurately, while the relative error in the expectation value of microscopic observables is much larger on average. We experimentally demonstrate the universality of some of these features in a state-of-the-art quantum simulator and show that the predicted behavior is generic for a highly accurate device, without assuming any detailed knowledge about the nature of the imperfections. |
Tuesday, March 16, 2021 2:06PM - 2:18PM Live |
F32.00012: Quantum supremacy in driven quantum many-body systems Jirawat Tangpanitanon, Supanut Thanasilp, Marc-Antoine Lemonde, Ninnat Dangniam, Dimitris Angelakis A crucial milestone in the field of quantum simulation and computation is to demonstrate that a quantum device can perform certain tasks that are impossible to reproduce by a classical computer with any reasonable resources. Such a demonstration is referred to as quantum supremacy. One of the most important questions is to identify setups that exhibit quantum supremacy and can be implemented with current quantum technology. Here, we show that quantum supremacy can be obtained in generic periodically-driven quantum many-body systems. Our analysis is based on the eigenstate thermalization hypothesis and strongly-held conjectures in complexity theory. To illustrate our work, we give examples of simple disordered Ising chains driven by global magnetic fields and Bose-Hubbard chains with modulated hoppings. Our proposal opens the way for a large class of quantum platforms to demonstrate and benchmark quantum supremacy. |
Tuesday, March 16, 2021 2:18PM - 2:30PM On Demand |
F32.00013: Neural network decoders on near term trapped-ion logical qubits David Obando Vargas, Yefry Lopez, Mauricio Gutierrez The implementation of a logical qubit with a higher fidelity than its constituent physical qubits is an essential process towards the construction of a fault tolerant quantum computer. Under this framework, we perform simulations of two promising distance-3 quantum error-correcting codes: the surface-17 and the Bacon-Shor codes, implemented on ion-traps with realistic noise sources. We use the syndromes of multiple error-correcting cycles and employ neural networks (NN) as decoders, with the goal of preserving the syndrome history and increasing the flexibility to different noise models. Under certain noise conditions, we find an improvement in the logical fidelity with the NN-based decoder compared to the most commonly used minimum-weight perfect matching and look-up table decoders |
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