Variational preparation of finite-temperature states on a quantum computer

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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• Variational Gibbs State Preparation on NISQ devices
• Extending the Variational Quantum Eigensolver to Finite Temperatures
• Qutrit and Qubit Circuits for Three-Flavor Collective Neutrino Oscillations
• Multi-Level Variational Spectroscopy using a Programmable Quantum Simulator
• Thermal variational quantum simulation on a superconducting quantum processor
• Critical behavior of Ising model by preparing thermal state on quantum computer
• Emergence of steady quantum transport in a superconducting processor
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• Fermionic Simulators for Enhanced Scalability of Variational Quantum Simulation
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• Variational quantum computing for quantum simulation: principles, implementations, and challenges
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• Rapid on-demand generation of thermal states in superconducting quantum circuits
• Hamiltonian Forging of a Thermofield Double
• Multi-target quantum compilation algorithm
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• Variational Quantum Algorithms for Gibbs State Preparation
• Gibbs state sampling via cluster expansions
• Dynamic thermalization on noisy quantum hardware