Minimal-backaction work statistics of coherent engines

TL;DR

This paper introduces a minimally invasive measurement scheme for quantum engines that preserves coherence and accurately captures work statistics, contrasting with traditional methods that disturb the system and can alter engine behavior.

Contribution

It presents a dynamic Bayesian network-based measurement approach that maintains quantum coherence and provides a reliable framework for energy exchange analysis in quantum engines.

Findings

The scheme preserves quantum coherence during measurements.

It accurately reproduces the unmeasured state's work statistics.

Universal fluctuation bounds may not hold for coherent quantum engines.

Abstract

Determining the work statistics of quantum engines is challenging due to measurement backaction. We here show that a dynamic Bayesian network-based measurement scheme, which preserves quantum coherence within an engine cycle, is minimally invasive, in the sense that the averaged measured state over one cycle exactly coincides with the unmeasured state. It therefore provides a general framework to investigate energy exchange statistics in quantum machines. This stands in contrast to the standard two-point measurement protocol, whose backaction can be so strong that it generally fails to reproduce the average work output of a coherent motor. It may even alter its mode of operation, causing it to cease functioning as an engine under observation. We further demonstrate that recently proposed universal fluctuation bounds do not necessarily apply to coherent machines.