Variational preparation of finite-temperature states on a quantum computer

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