Probing quantum puddles: nonlinear dynamics in superfluid film optomechanics

Abstract

In this thesis, we have cooled an optical ring resonator to a fraction of a degree above absolute zero and condensed a very thin film of superfluid helium on top of it. With this setup we are able to measure the height of the superfluid film with an accuracy of the size of an atom. The superfluid film can move similar to trampoline or drumhead and supports different mechanical modes. Using a tiny fraction of the power produced by a light bulb, we investigated what happens when we drive the motion of the superfluid helium to large amplitudes. We observed a sudden jump in the amplitude of a superfluid mechanical mode, the mechanical lasing regime, and investigated the impact of the temperature and the thickness of this film on the mechanical lasing. Finally, we controlled the motion of multiple mechanical modes supported by the superfluid films, such that they together form separated pulses. This is called mode-locked lasing and is only possible through the direct interaction of the mechanical modes.