Non-Markovian sensing of a quantum reservoir

TLDR

Quantum sensing uses quantum resources to achieve highly sensitive measurements, typically relying on unitary dynamics to encode quantities into sensor states. The authors aim to measure the spectral density of a quantum reservoir, a key factor in controlling reservoir‑induced decoherence, by proposing a nonunitary‑encoding optical sensing scheme. Their scheme employs nonunitary dynamics that encode information into the sensor, turning encoding time and sensor squeezing into resources that enhance precision and surpass the shot‑noise limit. The approach succeeds because a sensor‑reservoir bound state forms, enabling efficient reservoir measurement and offering support for decoherence control.

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.