Quantum-enhanced Markov chain Monte Carlo
This work addresses a bottleneck in sampling for fields such as statistical physics and machine learning, offering a near-term quantum advantage for useful problems, though it is incremental as it builds on existing MCMC techniques.
The paper tackles the problem of sampling from complicated probability distributions, which is a bottleneck in applications like statistical physics and machine learning, by introducing a quantum-enhanced Markov chain Monte Carlo algorithm that converges in fewer iterations than classical alternatives on relevant problem instances, as demonstrated in simulations and experiments.
Sampling from complicated probability distributions is a hard computational problem arising in many fields, including statistical physics, optimization, and machine learning. Quantum computers have recently been used to sample from complicated distributions that are hard to sample from classically, but which seldom arise in applications. Here we introduce a quantum algorithm to sample from distributions that pose a bottleneck in several applications, which we implement on a superconducting quantum processor. The algorithm performs Markov chain Monte Carlo (MCMC), a popular iterative sampling technique, to sample from the Boltzmann distribution of classical Ising models. In each step, the quantum processor explores the model in superposition to propose a random move, which is then accepted or rejected by a classical computer and returned to the quantum processor, ensuring convergence to the desired Boltzmann distribution. We find that this quantum algorithm converges in fewer iterations than common classical MCMC alternatives on relevant problem instances, both in simulations and experiments. It therefore opens a new path for quantum computers to solve useful--not merely difficult--problems in the near term.