Destructive Error Interference in Product-Formula Lattice Simulation

TL;DR

This paper demonstrates that errors in product-formula quantum simulations can interfere destructively, leading to significantly reduced error bounds and more efficient simulation estimates for physically relevant systems.

Contribution

It proves a tighter error bound for product-formula simulations by analyzing destructive error interference, improving upon previous estimates.

Findings

Error interference reduces simulation error significantly.

Tighter bounds match empirical performance.

Potential for further improvements suggested by numerical evidence.

Abstract

Quantum computers can efficiently simulate the dynamics of quantum systems. In this paper, we study the cost of digitally simulating the dynamics of several physically relevant systems using the first-order product formula algorithm. We show that the errors from different Trotterization steps in the algorithm can interfere destructively, yielding a much smaller error than previously estimated. In particular, we prove that the total error in simulating a nearest-neighbor interacting system of $n$ sites for time $t$ using the first-order product formula with $r$ time slices is $O({nt}/{r}+{nt^3}/{r^2})$ when $nt^2/r$ is less than a small constant. Given an error tolerance $\epsilon$, the error bound yields an estimate of $\max\{O({n^2t}/{\epsilon}),O({n^2 t^{3/2}}/{\epsilon^{1/2}})\}$ for the total gate count of the simulation. The estimate is tighter than previous bounds and matches the empirical performance observed in Childs et al. [PNAS 115, 9456-9461 (2018)]. We also provide numerical evidence for potential improvements and conjecture an even tighter estimate for the gate count.