Quantum Noise in Differential-type Gravitational-wave Interferometer and Signal Recycling

TL;DR

This paper demonstrates that signal recycling can be applied to differential-type gravitational-wave interferometers, improving sensitivity and signal-to-noise ratio for various binary systems by leveraging quantum noise correlations.

Contribution

It extends the concept of signal recycling to differential-type interferometers and shows how it enhances sensitivity and SNR, which was previously considered only in recombined-type setups.

Findings

Signal recycling is feasible in differential-type interferometers.

Up to three dips can appear in the sensitivity curve due to signal recycling.

SNR improvements of up to 2.94 times for black hole binaries.

Abstract

There exists the standard quantum limit (SQL), derived from Heisenberg's uncertainty relation, in the sensitivity of laser interferometer gravitational-wave detectors. However, in the context of a full quantum-mechanical approach, SQL can be overcome using the correlation of shot noise and radiation-pressure noise. So far, signal recycling, which is one of the methods to overcome SQL, is considered only in a recombined-type interferometer such as Advanced-LIGO, LCGT, and GEO600. In this paper, we investigated quantum noise and the possibility of signal recycling in a differential-type interferometer. As a result, we found that signal recycling is possible and creates at most three dips in the sensitivity curve of the detector. Then, taking advantage of the third additional dip and comparing the sensitivity of a differential-type interferometer with that of a next-generation Japanese GW interferometer, LCGT, we found that SNR of inspiral binary is improved by a factor of 1.43 for neutron star binary, 2.28 for 50 M_sun black hole binary, and 2.94 for 100 M_sun black hole binary. We also found that power recycling to increase laser power is possible in our signal-recycling configuration of a detector.