Proposal for Gravitational-Wave Detection Beyond the Standard Quantum Limit via EPR Entanglement

TL;DR

This paper proposes a novel method using EPR entanglement to surpass the Standard Quantum Limit in gravitational-wave detection without requiring a filter cavity, enhancing future detector sensitivity.

Contribution

It introduces a filter-cavity-free approach leveraging EPR entanglement to achieve frequency-dependent squeezing in gravitational-wave detectors.

Findings

Eliminates the need for a filter cavity in quantum noise reduction.

Utilizes EPR entanglement to engineer frequency-dependent squeezing.

Applicable to all future gravitational-wave detectors.

Abstract

The Standard Quantum Limit in continuous monitoring of a system is given by the trade-off of shot noise and back-action noise. In gravitational-wave detectors, such as Advanced LIGO, both contributions can simultaneously be squeezed in a broad frequency band by injecting a spectrum of squeezed vacuum states with a frequency-dependent squeeze angle. This approach requires setting up an additional long base-line, low-loss filter cavity in a vacuum system at the detector's site. Here, we show that the need for such a filter cavity can be eliminated, by exploiting EPR-entangled signal and idler beams. By harnessing their mutual quantum correlations and the difference in the way each beam propagates in the interferometer, we can engineer the input signal beam to have the appropriate frequency dependent conditional squeezing once the out-going idler beam is detected. Our proposal is appropriate for all future gravitational-wave detectors for achieving sensitivities beyond the Standard Quantum Limit.