High Power Interferometric Phase Measurement Limited by Quantum Noise and Application to Detection of Gravitational Waves

Interferometric detection of gravitational waves at levels of astrophysical interest is expected to require measurement of optical phase differences of ≤10^-10 rad. To achieve this sensitivity the measurement must be made at the quantum (shot noise) limit. We have built a laboratory-scale interferometer to investigate limits to sensing the phase at this level, and obtained, with 70 W of circulating power, a phase sensitivity limited by shot noise of 3×10^-100ex0exrad/√Hz at frequencies above 1.5 kHz. We describe the experiment and discuss the implications for the Laser Interferometer Gravitational-Wave Observatory (LIGO).