Quantum noise in second generation, signal-recycled laser interferometric gravitational-wave detectors

TL;DR

This paper demonstrates that second-generation laser interferometric gravitational-wave detectors can surpass the Standard Quantum Limit by exploiting quantum correlations, leading to improved sensitivity over a broad frequency range.

Contribution

It provides a fully quantum-mechanical analysis showing how quantum correlations in a signal-recycled interferometer can beat the Standard Quantum Limit.

Findings

Quantum shot noise and radiation-pressure noise are correlated.

The noise curve has two resonant dips.

The Standard Quantum Limit can be exceeded by a factor of 2.

Abstract

It has long been thought that the sensitivity of laser interferometric gravitational-wave detectors is limited by the free-mass standard quantum limit, unless radical redesigns of the interferometers or modifications of their input/output optics are introduced. Within a fully quantum-mechanical approach we show that in a second-generation interferometer composed of arm cavities and a signal recycling cavity, e.g., the LIGO-II configuration, (i) quantum shot noise and quantum radiation-pressure-fluctuation noise are dynamically correlated, (ii) the noise curve exhibits two resonant dips, (iii) the Standard Quantum Limit can be beaten by a factor of 2, over a frequency range \Delta f/f \sim 1, but at the price of increasing noise at lower frequencies.