Phys. Rev. X 3, 031012 (2013)

An optomechanical method known as ponderomotive squeezing has been difficult to realize experimentally because it requires a large interaction between mechanical motion and quantum fluctuations of light. Now, Tom Purdy and a team from JILA, the National Institute of Standards and Technology, and the University of Colorado, Boulder, have observed ponderomotive squeezing at 1.7 dB below the shot-noise level and optical amplification of quantum fluctuations by over 25 dB. This was enabled by using light transmitted through a Fabry–Pérot optical cavity with an embedded, dielectric membrane that can flex. The cavity was 3.54 mm long and the membrane was a 500-μm2 silicon nitride membrane that was 40 nm thick. Maximal squeezing occurred near the resonant frequency of the mechanical membrane. The results agree with a theoretical model with calibrated parameters that accounts for the thermal motion of the membrane with no other classical noise sources. Although stronger squeezing has been demonstrated before using various other approaches, the team notes that the ultimate limits of ponderomotively squeezed light have yet to be reached.