Fundamental sensitivity limit of lossy cavity-enhanced interferometers with external and internal squeezing

TL;DR

This paper derives the fundamental sensitivity limit of lossy cavity-enhanced interferometers with external and internal squeezing, showing how internal squeezing can mitigate optical loss and improve weak force detection.

Contribution

It introduces an optimal internal squeezing technique to reach the ultimate sensitivity limits of cavity and squeezed-light sensors under realistic loss conditions.

Findings

Internal squeezing mitigates readout loss effectively.

The fundamental sensitivity limit is derived considering optical decoherence.

Application scenarios confirm improved sensitivity with internal squeezing.

Abstract

Quantum optical sensors are ubiquitous in various fields of research, from biological or medical sensors to large-scale experiments searching for dark matter or gravitational waves. Gravitational-wave detectors have been very successful in implementing cavities and quantum squeezed light for enhancing sensitivity to signals from black hole or neutron star mergers. However, the sensitivity to weak forces is limited by available energy and optical decoherence in the system. Here, we derive the fundamental sensitivity limit of cavity and squeezed-light enhanced interferometers with optical loss.This limit is attained by the optimal use of an additional internal squeeze operation, which allows to mitigate readout loss. We demonstrate the application of internal squeezing to various scenarios and confirm that it indeed allows to reach the best sensitivity in cavity and squeezed-light enhanced linear force sensors. Our work establishes the groundwork for the future development of optimal sensors in real-world scenarios where, up until now, the application of squeezed light was curtailed by various sources of decoherence.