Observation of a partially rotating superfluid of exciton-polariton

TL;DR

This paper reports the experimental observation that exciton-polariton superfluids can exhibit both irrotational and rotational components, allowing continuous tuning of angular momentum, which advances understanding of non-equilibrium superfluid properties.

Contribution

It demonstrates that exciton-polariton superfluids can be partially rotating with controllable angular momentum, a novel behavior not seen in traditional superfluids.

Findings

Exciton-polariton superfluid can split into irrotational and rotational parts.

The ratio of these parts is controllable via pump power or spot size.

Angular momentum can be tuned from zero to Nħ continuously.

Abstract

Rotation of a container holding a viscous fluid forms a vortex which grows with increasing angular velocity. A superfluid, however, is intrinsically different from these normal fluids because its rotation is quantized. Even if a container of superfluid is rotating, the fluid itself remains still until a critical velocity is reached. Beyond the critical velocity, all the particles conspire to suddenly pick up an angular momentum of $\hbar$ each and forms a quantized vortex. As a result, a superfluid is known to increase its rotation by a total angular momentum of $N\hbar$. In this letter, we show that exciton-polariton superfluid can split into an irrotational part and a rotational part. The relative ratio between the two states can be controlled by either pump beam's power or spot size. Consequently, angular momentum of exciton-polariton superfluid can be tuned from zero to $N\hbar$ continuously. This striking observation sets the stage for studying non-equilibrium properties of a superfluid with exciton-polaritons.