Squeezed Light in a Cryogenic Optomechanical System

Frequency-dependent squeezed states are quantum states of light that allow measurements to beat the Standard Quantum Limit, providing sensitivity improvements to gravitational wave interferometers and improving optomechanics and quantum computing experiments. A tabletop optics frequency-dependent squeezed light (FDSL) generator and phononic crystal membrane experiment at the Kastler Brossel Laboratory (LKB) in Paris were optimized, with the goal of eventually combining the two experiments into a larger FDSL cryogenic optomechanical system. In the squeezed light generator, devices were designed to improve the crystal positioning in the SHG and OPO in order to ease mode matching. The SHG was aligned and mode-matched, with an optimized conversion efficiency of 54.3%, superb for squeezing purposes. Future work involves optimizing the OPO, mode cleaner, and filter cavity before making a final measurement of FDSL, which is expected to be an improvement from LKB's previous tabletop squeezer. In the membrane experiment, a Q factor of 56,793 was obtained for a square SiN membrane at room temperature and atmospheric pressure, comparable to values in the literature. Two novel phononic crystal membranes—the Lotus and Dahlia—were designed and the first wafers were fabricated in the clean room. Future work involves testing phononic crystal membranes in cavities of various sizes and under cryogenic vacuum conditions as well as comparing the two designs to determine the optimal design for the final cryogenic optomechanics experiment.