Levitated Superfluid Helium Drops for Optomechanics

Superfluid helium is a material with considerable potential for use in cavity optomechanics. These include low optical absorption, low mechanical loss, low temperatures, low stiffness, and high thermal conductivity. In addition, isolated drops of liquid helium cool to roughly 300 mK via evaporation.

I will describe measurements of mm-scale drops of superfluid helium that are magnetically levitated in ultrahigh vacuum. We have found that the drops can be retained for months at a time, and that their bulk temperature and the noise temperature of their surface modes both reach T= 300 mK. Precise measurements of the drop's surface modes show good agreement with theory, along with signatures of the non-Markovian nature of the phonon gas within the drop. We have measured optical whispering gallery modes in the drop with finesse approaching 10^3, and shown that they exert the standard "optical spring" effect on the drop's surface modes.