Fast, accurate, high-resolution simulation of large-scale Fermi-Hubbard models on a digital quantum processor

TL;DR

This paper demonstrates large-scale, high-resolution digital quantum simulation of the 1D Fermi-Hubbard model on a superconducting quantum processor, surpassing classical simulation capabilities in accuracy and speed.

Contribution

It introduces an efficient encoding and error suppression techniques enabling simulation of large fermionic systems with up to 120 qubits, achieving results beyond classical methods.

Findings

Direct observation of spin-charge separation at scale

Quantum outputs match classical TDVP simulations within 1% RMSE

Quantum processor runs up to 3000 times faster than classical TDVP for long evolutions

Abstract

We report experimental digital quantum simulation of the one-dimensional Fermi-Hubbard model on a superconducting quantum processor at a scale beyond the reach of exact statevector simulation and challenging for state-of-the-art tensor-network methods. We encode this problem using up to 120 qubits through an efficient mapping that reduces circuit complexity, and we improve accuracy through error suppression to simulate dynamical evolution using up to 90 Trotter steps. From a vacancy defect introduced in the middle of an $L=31$-site (62-qubit) N\'{e}el initial state, we directly observe spin-charge separation to $t=9$ in natural units using up to 90 Trotter steps, and quantitatively extract velocity ratios $v_c/v_s$ which match classical simulations across a range of model parameters. We then extend experiments to $L=60$ (120 qubits) and long evolution times to $t=6$ using 30 Trotter steps; Quantum-processor outputs agree quantitatively with approximate classical simulations performed using a time-dependent variational principle (TDVP) solver; increasing the TDVP bond dimension through $\chi = 4096$ expands the range of evolution times within which agreement has RMSE $\sim 1\%$ before the approaches diverge. Owing to the large scale of the simulation and the use of efficient overhead-free error-suppression techniques, for simulated evolution times at the limit of quantum/classical agreement ($t\gtrsim 5$ in natural hopping units), the wall-clock runtime of the quantum processor is up to $3000\times$ faster than an optimized TDVP simulation using $\chi = 4096$. These results establish contemporary digital quantum processors as a versatile, quantitatively accurate, and competitive platform for the study of fermionic many-body dynamics in regimes where leading classical methods can become prohibitively expensive.