Non-Markovian Sensing of a Quantum Reservoir

TL;DR

This paper introduces a novel nonunitary optical sensing scheme for measuring quantum reservoir spectral density, leveraging sensor-reservoir bound states to enhance precision beyond shot-noise limits despite nonunitary dynamics.

Contribution

It proposes a new nonunitary-encoding quantum sensing method that utilizes sensor-reservoir bound states to improve measurement precision of quantum reservoirs.

Findings

Sensor-reservoir bound states enable surpassing shot-noise limit.

Nonunitary dynamics can be harnessed as a resource for sensing.

Sensor squeezing and encoding time improve measurement accuracy.

Abstract

Quantum sensing explores protocols using the quantum resource of sensors to achieve highly sensitive measurement of physical quantities. The conventional schemes generally use unitary dynamics to encode quantities into sensor states. In order to measure the spectral density of a quantum reservoir, which plays a vital role in controlling the reservoir-caused decoherence to microscopic systems, we propose a nonunitary-encoding optical sensing scheme. Although the nonunitary dynamics for encoding in turn degrades the quantum resource, we surprisingly find a mechanism to make the encoding time a resource to improve the precision and to make the squeezing of the sensor a resource to surpass the shot-noise limit. Our result shows that it is due to the formation of a sensor-reservoir bound state. Enriching the family of quantum sensing, our scheme gives an efficient way to measure the quantum reservoir and might supply an insightful support to decoherence control.