ABSTRACT
We characterize the mechanisms of vortex pinning in a superfluid thin film described by the two-dimensional Gross-Pitaevskii equation. We consider a vortex "scattering experiment" whereby a single vortex in a superfluid flow interacts with a circular, uniform pinning potential. By an analogy with linear dielectrics, we develop an analytical hydrodynamic approximation that predicts vortex trajectories, the vortex fixed point and the unpinning velocity. We then solve the Gross-Pitaevskii equation to validate this model, and build a phase portrait of vortex pinning. We identify two different dynamical pinning mechanisms marked by distinctive phonon emission signatures: one enabled by acoustic radiation and another mediated by vortex dipoles nucleated within the pin. Relative to obstacle size, we find that pinning potentials on the order of the healing length are more effective for vortex capture. Our results could be useful in mitigating the negative effects of drag due to vortices in superfluid channels, in analogy to maximizing supercurrents in type-II superconductors.
ABSTRACT
Quantized vortices are fundamental to the two-dimensional dynamics of superfluids, from quantum turbulence to phase transitions. However, surface effects have prevented direct observations of coherent two-dimensional vortex dynamics in strongly interacting systems. Here, we overcome this challenge by confining a thin film of superfluid helium at microscale on the atomically smooth surface of a silicon chip. An on-chip optical microcavity allows laser initiation of clusters of quasi-two-dimensional vortices and nondestructive observation of their decay in a single shot. Coherent dynamics dominate, with thermal vortex diffusion suppressed by five orders of magnitude. This establishes an on-chip platform with which to study emergent phenomena in strongly interacting superfluids and to develop quantum technologies such as precision inertial sensors.
