Overhead-constrained circuit knitting for variational quantum dynamics

TL;DR

This paper introduces an overhead-constrained circuit knitting approach combined with PVQD to enable scalable, accurate simulation of large quantum system dynamics on limited quantum hardware, reducing circuit depth and sampling overhead.

Contribution

It presents a novel circuit knitting method with parameter constraints to simulate large quantum systems efficiently on small, noisy quantum devices.

Findings

Accurately simulates quantum spin dynamics with manageable sampling overhead.

Reduces circuit depth by cutting long-range gates.

Demonstrates effectiveness on weakly entangled blocks.

Abstract

Simulating the dynamics of large quantum systems is a formidable yet vital pursuit for obtaining a deeper understanding of quantum mechanical phenomena. While quantum computers hold great promise for speeding up such simulations, their practical application remains hindered by limited scale and pervasive noise. In this work, we propose an approach that addresses these challenges by employing circuit knitting to partition a large quantum system into smaller subsystems that can each be simulated on a separate device. The evolution of the system is governed by the projected variational quantum dynamics (PVQD) algorithm, supplemented with constraints on the parameters of the variational quantum circuit, ensuring that the sampling overhead imposed by the circuit knitting scheme remains controllable. We test our method on quantum spin systems with multiple weakly entangled blocks each consisting of strongly correlated spins, where we are able to accurately simulate the dynamics while keeping the sampling overhead manageable. Further, we show that the same method can be used to reduce the circuit depth by cutting long-ranged gates.