Coherent quantum annealing in a programmable 2,000 qubit Ising chain

• Published in: Nature physics 2022-11, Vol.18 (11), p.1324-1328
• Main Authors: King, Andrew D., Suzuki, Sei, Raymond, Jack, Zucca, Alex, Lanting, Trevor, Altomare, Fabio, Berkley, Andrew J., Ejtemaee, Sara, Hoskinson, Emile, Huang, Shuiyuan, Ladizinsky, Eric, MacDonald, Allison J. R., Marsden, Gaelen, Oh, Travis, Poulin-Lamarre, Gabriel, Reis, Mauricio, Rich, Chris, Sato, Yuki, Whittaker, Jed D., Yao, Jason, Harris, Richard, Lidar, Daniel A., Nishimori, Hidetoshi, Amin, Mohammad H.
• Format: Article
• Language: English
• Subjects: 639/301/119/2795; 639/766/1130/1064; 639/766/483/3926; Atomic; Chains; Classical and Continuum Physics; Coherence; Complex Systems; Condensed Matter Physics; Exact solutions; Ising model; Letter; Machine learning; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Optimization; Phase transitions; Physics; Physics and Astronomy; Quantum theory; Qubits (quantum computing); Simulation; Temperature effects; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-022-01741-6

Quantum simulation has emerged as a valuable arena for demonstrating and understanding the capabilities of near-term quantum computers 1 – 3 . Quantum annealing 4 , 5 has been successfully used in simulating a range of open quantum systems, both at equilibrium 6 – 8 and out of equilibrium 9 – 11 . However, in all previous experiments, annealing has been too slow to coherently simulate a closed quantum system, due to the onset of thermal effects from the environment. Here we demonstrate coherent evolution through a quantum phase transition in the paradigmatic setting of a one-dimensional transverse-field Ising chain, using up to 2,000 superconducting flux qubits in a programmable quantum annealer. In large systems, we observe the quantum Kibble–Zurek mechanism with theoretically predicted kink statistics, as well as characteristic positive kink–kink correlations, independent of temperature. In small chains, excitation statistics validate the picture of a Landau–Zener transition at a minimum gap. In both cases, the results are in quantitative agreement with analytical solutions to the closed-system quantum model. For slower anneals, we observe anti-Kibble–Zurek scaling in a crossover to the open quantum regime. The coherent dynamics of large-scale quantum annealers demonstrated here can be exploited to perform approximate quantum optimization, machine learning and simulation tasks. The coherent dynamics of the transverse-field Ising model driven through a quantum phase transition can be accurately simulated using a large-scale quantum annealer.