Doubling the size of quantum simulators by entanglement forging

TL;DR

This paper introduces a classical-quantum hybrid method called entanglement forging that enables simulating larger quantum systems on existing hardware by offloading some computation to classical processing.

Contribution

The authors develop a novel classical entanglement forging technique that doubles the size of quantum simulations feasible on current quantum processors.

Findings

Simulated water molecule ground state energy with high accuracy

Represented ten spin-orbitals on five qubits using entanglement forging

Provided a scalable roadmap for larger quantum simulations

Abstract

Quantum computers are promising for simulations of chemical and physical systems, but the limited capabilities of today's quantum processors permit only small, and often approximate, simulations. Here we present a method, classical entanglement forging, that harnesses classical resources to capture quantum correlations and double the size of the system that can be simulated on quantum hardware. Shifting some of the computation to classical post-processing allows us to represent ten spin-orbitals on five qubits of an IBM Quantum processor to compute the ground state energy of the water molecule in the most accurate simulation to date. We discuss conditions for applicability of classical entanglement forging and present a roadmap for scaling to larger problems.