Variational preparation of finite-temperature states on a quantum computer (Part 2: experiment)*

The preparation of thermal equilibrium states is important for the simulation of condensed-matter and cosmology systems using a quantum computer. 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 varies smoothly from 99% at infinite temperature to 75% at near-zero temperature. We find quantitative agreement with a numerical simulation of our quantum processor with error parameters drawn from experiment.