“Optomechanics Inside a Levitated Superfluid Helium-4 Drop”
The levitation of mechanical systems allows for high environmental isolation. At the same time, an external laser can probe tiny forces and displacements, and exert a radiation pressure force to control its motion. In this talk, I will describe ongoing experiments with magnetically levitated superfluid Helium-4 drops that form our optomechanical system. The mechanical modes are surface oscillations around the spherical equilibrium shape, dispersively coupled to its optical whispering gallery modes (WGMs), serving as our optical cavity.
We can generate drops up to 0.8 mm in diameter that can survive indefinitely in ultrahigh vacuum (≤ 3×10^-11 mbar). In order to control and probe the internal degrees of freedom of the drop, we optically feedback to its center of mass motion and control its evaporation rate with cryo-bake outs (dR/dt ≥ 0.3 pm/s).
We have measured the oscillation frequencies of the drop’s free surface (amplitude ≤ 5 nm) with an agreement to ~ 1 part in 10^4 with ab initio theory, providing precise measurement of its diameter. We have also observed WGMs with Finesses up to 1000, and our ongoing efforts focus on enhanced detection of even higher-finesse WGMs and quantifying the optomechanical coupling strength.
Host: Yu-Han Tseng