A quantum-enhanced prototype gravitational-wave detector

Abstract

Substantial improvements, through the use of squeezed light, in the sensitivity of a prototype gravitational-wave detector built with quasi-free suspended optics represents the next step in moving such devices out of the lab and into orbit. The quantum nature of the electromagnetic field imposes a fundamental limit on the sensitivity of optical precision measurements such as spectroscopy, microscopy and interferometry1. The so-called quantum limit is set by the zero-point fluctuations of the electromagnetic field, which constrain the precision with which optical signals can be measured2,3,4. In the world of precision measurement, laser-interferometric gravitational-wave detectors4,5,6 are the most sensitive position meters ever operated, capable of measuring distance changes of the order of 10−18 m r.m.s. over kilometre separations caused by gravitational waves from astronomical sources7. The sensitivity of currently operational and future gravitational-wave detectors is limited by quantum optical noise6. Here, we demonstrate a 44% improvement in displacement sensitivity of a prototype gravitational-wave detector with suspended quasi-free mirrors at frequencies where the sensitivity is shot-noise-limited, by injecting a squeezed state of light1,2,3. This demonstration is a critical step towards implementation of squeezing-enhancement in large-scale gravitational-wave detectors.