Optomechanics for Quantum Noise Reduction in Gravitational Wave Detectors

Louisiana State University, Baton Rouge LA

Investigators

Abstract

The direct detection of gravitational waves emitted by a coalescing binary black hole system by the LIGO detectors in 2015 marked the beginning of gravitational wave astronomy. The detection of gravitational waves from a coalescing binary neutron star system coincident with a gamma ray burst, with follow-up observations by traditional telescopes, demonstrated the power of multimessenger astronomy and the potential it holds. To continue making these discoveries, improvements to the sensitivity of existing gravitational wave observatories must be made, and the physics that will make the next generation of detectors possible must be developed. Quantum fluctuations of the laser fields used to measure gravitational waves will limit Advanced LIGO's sensitivity across most of its frequency bandwidth once it reaches design sensitivity. This project is focused on reducing the limitation of that quantum noise by exploiting the coupling of light to mechanical motion. This project combines several of the key components that will make the next generation of detectors possible. Optical experiments will be conducted with microfabricated mechanical resonators with masses on the order of 100 nanograms. Specifically, the group will study the interaction of non-classical, or squeezed, states of light in an optomechanical cavity that is limited by both radiation pressure and shot noise in a broad frequency bandwidth, as Advanced LIGO is expected to be once it reaches design sensitivity. In order to achieve this goal, AlGaAs mirrors will be cryogenically cooled and placed in a high finesse optical cavity. Cryogenic operation will allow the Standard Quantum Limit to be approached, or even surpassed. At that sensitivity, these devices are good candidates for employing optomechanical interactions in filter cavities. Optomechanical filter cavities manipulate the coupling between radiation pressure and the mechanical degrees of freedom of the system to produce certain effects in light passing through the cavity. In principle, these filter cavities may be used to condition squeezed states of light to produce a frequency dependence suitable for injection to gravitational wave interferometers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.