Quantum memory assisted observable estimation

TL;DR

This paper introduces Coherent Pauli Summation (CPS), a method leveraging a single-qubit quantum memory to efficiently estimate many-qubit observables, reducing measurement requirements and improving accuracy in noisy quantum devices.

Contribution

The paper presents a novel CPS method that uses a single-qubit quantum memory to enhance observable estimation, reducing measurement complexity compared to traditional approaches.

Findings

CPS reduces measurement count linearly with the number of Pauli strings.

The method improves variance scaling in observable estimation.

Demonstrates utility in noisy many-qubit quantum devices.

Abstract

The estimation of many-qubit observables is an essential task of quantum information processing. The generally applicable approach is to decompose the observables into weighted sums of multi-qubit Pauli strings, i.e., tensor products of single-qubit Pauli matrices, which can readily be measured with single qubit rotations. The accumulation of shot noise in this approach, however, severely limits the achievable variance for a finite number of measurements. We introduce a novel method, dubbed Coherent Pauli Summation (CPS) that circumvents this limitation by exploiting access to a single-qubit quantum memory in which measurement information can be stored and accumulated. Our algorithm offers a reduction in the required number of measurements for a given variance that scales linearly with the number of Pauli strings of the decomposed observable. Our work demonstrates how a single long-coherence qubit memory can assist the operation of noisy many-qubit quantum devices in a cardinal task.