Certified quantum non-demolition measurement of a macroscopic material system

TL;DR

This paper demonstrates a certified quantum non-demolition measurement of a macroscopic atomic ensemble's collective spin, surpassing classical limits and enabling advanced quantum information and metrology applications.

Contribution

It presents the first certified QND measurement of a macroscopic material system, achieving quantum state preparation and information-damage trade-off beyond classical bounds.

Findings

Quantum state preparation beyond classical limits

Information-damage trade-off surpassing classical bounds

Potential for quantum metrology and quantum information protocols

Abstract

Quantum non-demolition (QND) measurements improve sensitivity by evading measurement back-action. The technique was first proposed to detect mechanical oscillations in gravity wave detectors,and demonstrated in the measurement of optical fields, leading to the development of rigorous criteria to distinguish QND from similar non-classical measurements. Recent QND measurements of macroscopic material systems such as atomic ensembles, and mechanical oscillators, show some QND features, but not full QND character. Here we demonstrate certified QND measurement of the collective spin of an atomic ensemble. We observe quantum state preparation (QSP) and information-damage trade-off (IDT) beyond their classical limits by seven and twelve standard deviations, respectively. Our techniques complement recent work with microscopic systems, and can be used for quantum metrology and memory, the preparation and detection of non-gaussian states, and proposed quantum simulation and information protocols. They should enable QND measurements of dynamical quantum variables and the realization of QND-based quantum information protocols.