Enhancing interferometer sensitivity without sacrificing bandwidth and stability: beyond single-mode and resolved-sideband approximation

TL;DR

This paper demonstrates that a PT-symmetric optomechanical filter can enhance interferometer sensitivity and bandwidth without instability, even when moving beyond idealized approximations to realistic parameters.

Contribution

It extends previous PT-symmetric filter designs by analyzing stability without single-mode and resolved-sideband approximations, confirming robustness with realistic parameters.

Findings

System remains stable beyond idealized approximations

Nyquist analysis confirms stability

Time-domain simulations support robustness

Abstract

Quantum noise limits the sensitivity of precision measurement devices, such as laser interferometer gravitational-wave observatories and axion detectors. In the shot-noise-limited regime, these resonant detectors are subject to a trade-off between the peak sensitivity and bandwidth. One approach to circumvent this limitation in gravitational-wave detectors is to embed an anomalous-dispersion optomechanical filter to broaden the bandwidth. The original filter cavity design, however, makes the entire system unstable. Recently, we proposed the coherent feedback between the arm cavity and the optomechanical filter to eliminate the instability via PT-symmetry. The original analysis based upon the Hamiltonian formalism adopted the single-mode and resolved-sideband approximations. In this paper, we go beyond these approximations and consider realistic parameters. We show that the main conclusion concerning stability remains intact, with both Nyquist analysis and a detailed time-domain simulation.