Quantum-enhanced metrology with the single-mode coherent states of an optical cavity inside a quantum feedback loop

TL;DR

This paper demonstrates a quantum metrology scheme using a single-mode coherent state in an optical cavity with feedback, achieving phase measurement precision beyond the standard quantum limit using feasible current technology.

Contribution

It introduces a practical quantum-enhanced measurement method leveraging quantum feedback and coherent states, avoiding the need for entangled photon states.

Findings

Achieves phase measurement accuracy above the standard quantum limit.

Utilizes quantum feedback to enhance sensitivity without requiring high-efficiency detectors.

Compatible with current optical cavity technology.

Abstract

In this paper, we use the non-linear dynamics of the individual quantum trajectories of an optical cavity inside an instantaneous quantum feedback loop to measure the phase shift between two pathways of light with an accuracy above the standard quantum limit. The feedback laser provides a reference frame and constantly increases the dependence of the state of the resonator on the unknown phase. Since our quantum metrology scheme can be implemented with current technology and does not require highly-efficient single photon detectors, it should be of practical interest until highly-entangled many-photon states become more readily available.