Minimizing back-action through entangled measurements

TL;DR

This paper introduces a novel entangled measurement technique to significantly reduce measurement back-action in quantum systems, both theoretically and experimentally, especially effective in highly coherent processes.

Contribution

It presents a new entangled collective measurement method that minimizes measurement back-action beyond previous schemes, with theoretical and experimental validation.

Findings

Back-action can be greatly suppressed using entangled measurements.

The method is effective in highly coherent quantum processes.

Experimental results confirm theoretical predictions.

Abstract

When an observable is measured on an evolving coherent quantum system twice, the first measurement generally alters the statistics of the second one, which is known as measurement back-action. We introduce, and push to its theoretical and experimental limits, a novel method of back-action evasion, whereby entangled collective measurements are performed on several copies of the system. This method is inspired by a similar idea designed for the problem of measuring quantum work [Perarnau-Llobet \textit{et al}., (https://doi.org/10.1103/PhysRevLett.118.070601) Phys. Rev. Lett. \textbf{118}, 070601 (2017)]. By utilizing entanglement as a resource, we show that the back-action can be extremely suppressed compared to all previous schemes. Importantly, the back-action can be eliminated in highly coherent processes.