Observing and Evading Quantum Backaction in an Interferometer

Observing and Evading Quantum Backaction in an Interferometer 
N. S. Kampel, T. P. Purdy, P.-L. Yu, R. W. Peterson, and C. A. Regal

The pursuit to eliminate classical noise sources in an interferometer has a long history. Only recently have experimental conditions matured enough to enable measuring quantum backaction in the continuous displacement detection of a solid mechanical resonator. Moreover reaching the regime in which mechanical vacuum fluctuations dominate opens the door to variety of experiments, from ultra-high position and force sensitivity to producing mechanical quantum states.
We use a macroscopic silicon nitride membrane resonator in a high-finesse optical cavity to measure the quantum backaction put forth by a light probe. Here I present initial results of two experiments. In the first we avoid the quantum backaction, and in the second we measure evidence of the resonator being in the quantum mechanical ground state.