Approximate Hamiltonian Simulation Algorithm for Efficient Fluid Quantum Simulations

TL;DR

This paper introduces an approximate operator optimization scheme that significantly reduces circuit depth in quantum fluid simulations, enabling more efficient and scalable quantum computations of complex fluid dynamics.

Contribution

The work proposes a novel approximate Hamiltonian simulation algorithm that reduces circuit depth from O(n^2) to O(n log n) or O(n), improving efficiency for quantum fluid simulations.

Findings

Reduced circuit depth from O(n^2) to O(n log n) or O(n)

High correlation coefficients (>0.93) in fluid property simulations

Balanced truncation error and hardware noise for larger qubit systems

Abstract

This work aims to address the bottleneck issues of hardware resource limitation and decoherence error in the Hamiltonian simulation of quantum fluids, which are caused by the standard quantum Fourier transform and the evolution of momentum operators, resulting in excessively deep circuits and excessive two-qubit gates. We propose an approximate operator optimization scheme aimed at reducing the circuit depth in Hamiltonian evolution. The proposed scheme successfully reduces the depth of analog circuits from $O(n^2)$ to $O(nlogn)$ or even $O(n)$ by eliminating $O(n^2)$ redundant two-qubit entangling gates. In this work, the numerical experiments are implemented on a supercomputing-oriented quantum simulator, simulating two-dimensional unsteady divergent flow. Experimental results demonstrate that although the truncation of high-frequency qubit coupling terms introduces deterministic theoretical errors, scaling at $O(n)$ for AQFT and $O(n^2)$ for momentum truncation, the optimized simulations successfully preserve the inherent macroscopic temporal evolution characteristics of the fluid in a 10-qubit simulation, achieving high correlation coefficients of $r$=0.933, $r$=0.941, and $r$=0.977 for density, X-momentum, and Y-momentum distributions respectively. Furthermore, we also analyzed the relationship between the algorithm truncation error and the hardware cumulative noise when the qubit number is extended to a higher level. This study proves that rationally adjusting truncation thresholds can establish an equilibrium point, preventing the hardware cumulative error from rapidly approaching 100% at the 20-30 qubit scale, providing a feasible engineering pathway for simulating complex fluid systems on real quantum devices in the future.