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arXiv · 2012.03895

Variational preparation of finite-temperature states on a quantum computer

R. Sagastizabal·S. P. Premaratne·B. A. Klaver·M. A. Rol·V. Negîrneac·M. Moreira·X. Zou·S. Johri·N. Muthusubramanian·M. Beekman·C. Zachariadis·V. P. Ostroukh·N. Haider·A. Bruno·A. Y. Matsuura·L. DiCarlo
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Abstract

The preparation of thermal equilibrium states is important for the simulation of condensed-matter and cosmology systems using a quantum computer. We present a method to prepare such mixed states with unitary operators, and demonstrate this technique experimentally using a gate-based quantum processor. Our method targets the generation of thermofield double states using a hybrid quantum-classical variational approach motivated by quantum-approximate optimization algorithms, without prior calculation of optimal variational parameters by numerical simulation. The fidelity of generated states to the thermal-equilibrium state smoothly varies from 99 to 75% between infinite and near-zero simulated temperature, in quantitative agreement with numerical simulations of the noisy quantum processor with error parameters drawn from experiment.

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R. Sagastizabal, S. P. Premaratne, B. A. Klaver, M. A. Rol, V. Negîrneac, M. Moreira, X. Zou, S. Johri, N. Muthusubramanian, M. Beekman, C. Zachariadis, V. P. Ostroukh, N. Haider, A. Bruno, A. Y. Matsuura, L. DiCarlo. 2020-12-07. Variational preparation of finite-temperature states on a quantum computer. https://doi.org/10.1038/s41534-021-00468-1

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