Quantum-enhanced metrology without entanglement based on optical cavities with feedback

TL;DR

This paper presents a quantum metrology method using optical cavities with feedback that improves phase measurement precision without relying on entanglement or non-linearities, leveraging conditional dynamics of open quantum systems.

Contribution

It introduces a novel quantum metrology approach based on conditional dynamics in open quantum systems, avoiding the need for entanglement or non-linear interactions.

Findings

Achieves phase measurement enhancement without entangled photons.

Utilizes photon correlation measurements in optical cavities.

Potentially practical for real-world quantum sensing applications.

Abstract

There are a number of different strategies to measure the phase shift between two pathways of light more efficiently than suggested by the standard quantum limit. One way is to use highly entangled photons. Another way is to expose photons to a non-linear or interacting Hamiltonian. This paper emphasises that the conditional dynamics of open quantum systems provides an interesting additional tool for quantum-enhanced metrology. As a concrete example, we review a recent scheme which exploits the conditional dynamics of a laser-driven optical cavity with spontaneous photon emission inside a quantum feedback loop. Deducing information from second-order photon correlation measurements requires neither optical non-linearities nor entangled photons and should therefore be of immediate practical interest.