Quantum Optics and Mechanics in Gravitational-Wave Detectors

Abstract

Gravitational-wave detectors like Advanced LIGO probe perhaps the most cataclysmic events since the Big Bang, involving objects tens to hundreds of times more massive than the Sun, yet they remain at the whim of minute quantum fluctuations. Pushing our reach further into the cosmos demands a mastery over these quantum effects. In recent years, we have entered the era of quantum-enhanced gravitational-wave detection, wherein the injection of squeezed states has been demonstrated as an effective technique to suppress high-frequency vacuum fluctuations. As gravitational-wave detectors continue to improve, operating at higher powers with more squeezing and reduced classical noises, radiation pressure noise is increasingly becoming a limiting factor at low frequencies. Frequency-dependent squeezed sources circumvent this by appropriately rotating the quadrature of the injected squeezing so as to confer sensitivity improvements across the entirety of the gravitational-wave detection band.

In this thesis, we study the use of frequency-dependent squeezing in gravitational-wave detectors. We offer the first demonstration of a frequency-dependent squeezed source operating at frequencies useful for gravitational-wave detectors. To achieve this, we commissioned and operated a long, extremely-high-finesse optical cavity to a high degree of stability, compatible with the stringent requirements called for by the next iteration of LIGO: Advanced LIGO+.

At the same time, gravitational-wave detectors are just now reaching the sensitivities required to observe quantum effects on the kilogram-scale of the test masses. We use the superb displacement precision of Advanced LIGO to suppress the differential motion of the test masses to within 10% of the ground state.