Macroscopic mechanical devices in the quantum regime can play a key role in quantum communication, quantum sensing and fundamental tests of quantum mechanics. We use a fiber cavity filled with superfluid $^4$He of mass ~ 1 ng as our mechanical resonator. Leveraging single photon counting techniques, we manipulate and probe the motional state of a superfluid $^4$He resonator. The arrival times of Stokes and anti-Stokes photons are used to measure the resonator’s phonon coherences. We demonstrate the coherences of a thermal state near the motional ground state, a non-classical photon-phonon squeezed state, and a high amplitude coherent state in this superfluid $^4$He resonator. These measurements pave the avenue of realizing a non-classical state in a milligram resonator in future experiments.
|Presenter name||Wang, Yiqi|