Measuring High-Order Phonon Correlations in an Optomechanical Resonator

Abstract

We use single photon detectors to probe the motional state of a superfluid ${}^4$He resonator of mass $\sim 1$ ng. The arrival times of Stokes and anti-Stokes photons (scattered by the resonator's acoustic mode) are used to measure the resonator's phonon coherences up to the fourth order. By post-selecting on photon detection events, we also measure coherences in the resonator when $\le 3$ phonons have been added or subtracted. These measurements are found to be consistent with predictions that assume the acoustic mode to be in thermal equilibrium with a bath through a Markovian coupling.

Main text: 6 pages, 4 figures. Supplement: 13 pages, 11 figures

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