In this talk I will give a wide introduction to optomechanics and talk about the superfluid Helium device, that we designed and built in Jack Harris’ lab. I will describe how we couple modes of light and fluid and how we measure the motion of the modes in Helium. Finally, I will clarify which and how quantum effects are important in our optomechanical device.
Cavity optomechanics studies interactions between light confined to an optical or microwave cavity and mechanical objects (such as movable mirrors, membranes, nano-strings). The thermal or driven motion of the mechanical object can change the cavity’s resonance frequency. Cavity optomechanics has been used for frequency conversion between optical and microwave domains and precise readouts in sensors (e.g. LIGO), but is also currently investigated for the storage of quantum states, study of quantum limitations and mechanical decoherence due to gravity. We use superfluid Helium as the mechanical object because it hosts acoustic modes with low dissipation and has almost no impurities which could absorb or scatter light. It also offers some practical benefits, such as ease of alignment and high thermal conductivity (needed to keep low temperatures). Additionally, superfluid helium can serve as a host for other systems, such as vortices, excimers (2-level systems), ripplons (surface waves) that can be probed with light directly or indirectly (via acoustic modes).