Broadband sensitivity improvement via coherent quantum feedback with PT symmetry

TL;DR

This paper introduces a stable quantum amplifier leveraging PT symmetry and non-degenerate parametric amplification to enhance the bandwidth and sensitivity of linear quantum detectors, overcoming traditional trade-offs.

Contribution

It proposes a novel PT-symmetric quantum amplifier design that improves detector sensitivity and bandwidth without instability, applicable to gravitational-wave and axion detection.

Findings

Sensitivity improved for gravitational-wave detectors

Enhanced bandwidth in microwave cavity axion detectors

Stable operation at the quantum detection limit

Abstract

A conventional resonant detector is often subject to a trade-off between bandwidth and peak sensitivity that can be traced back to quantum Cramer-Rao Bound. Anomalous dispersion has been shown to improve it by signal amplification and is thus more robust against decoherence, while it leads to instabilities. We propose a stable quantum amplifier applicable to linear systems operating at the fundamental detection limits, enabled by two-mode non-degenerate parametric amplification. At threshold, one mode of the amplifier forms a PT-symmetric system of original detector mode. Sensitivity improvements are shown for laser-interferometric gravitational-wave detectors and microwave cavity axion detectors.