Fontana Enrico, Rudolph Manuel S, Duncan Ross, Rungger Ivan, Cîrstoiu Cristina
Department of Computer and Information Sciences, University of Strathclyde, Glasgow, UK.
Quantinuum, Cambridge, UK.
npj Quantum Inf. 2025;11(1):84. doi: 10.1038/s41534-024-00955-1. Epub 2025 May 22.
Noise detrimentally affects quantum computations so that they not only become less accurate but also easier to simulate classically as systems scale up. We construct a classical simulation algorithm, lowesa (low weight efficient simulation algorithm), for estimating expectation values of noisy parameterised quantum circuits with a fixed observable. It combines previous results on spectral analysis of parameterised circuits with Pauli back-propagation and recent ideas for simulations of noisy random circuits. We show, under some conditions on the circuits and mild assumptions on noise, that lowesa gives an efficient, polynomial algorithm in the number of qubits (and depth), with approximation error that vanishes exponentially in the physical error rate and a controllable cutoff parameter. This is valid for any expectation value that may be efficiently evaluated on a quantum computer. We discuss the practical limitations of the method for circuit classes with correlated parameters and its scaling with decreasing error rates.
噪声对量子计算有不利影响，以至于随着系统规模扩大，它们不仅变得精度降低，而且在经典模拟中也更容易。我们构建了一种经典模拟算法，即lowesa（低权重高效模拟算法），用于估计具有固定可观测量的含噪参数化量子电路的期望值。它将先前关于参数化电路谱分析与泡利反向传播的结果，以及近期关于含噪随机电路模拟的想法结合起来。我们表明，在电路的某些条件和对噪声的适度假设下，lowesa给出了一种关于量子比特数（和深度）的高效多项式算法，其近似误差在物理错误率中呈指数级消失，且有一个可控的截止参数。这对于任何可在量子计算机上有效评估的期望值都是有效的。我们讨论了该方法对于具有相关参数的电路类别的实际局限性及其随错误率降低的缩放情况。
