Improving broadband displacement detection via quantum correlations in an interferometer
The pursuit of increasingly sensitive interferometric measurement of mechanical motion has a rich history. This pursuit has resulted in the development and study of seminal ideas on quantum limits of measurement and how to improve measurements in the face of seeming limitations. In recent years, an interesting class of devices has been developed in which low-mass, high-frequency, and mechanically isolated objects are coupled to optical cavities. The large response of these mechanical objects to applied forces makes them an ideal platform to observe the effects of radiation forces. We can now cool mechanical membranes well into their quantum ground state and routinely observe the effect of a fluctuating radiation pressure force due to optical shot noise. Our recent measurements study a technique to improve interferometric displacement detection known as variational readout.