Observation of a partially rotating superfluid of exciton-polariton

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 $\hslash$ each and forms a quantized vortex. As a result, a superfluid is known to increase its rotation by a total angular momentum of $N\hslash$. 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 $N\hslash$ continuously. This striking observation sets the stage for studying non-equilibrium properties of a superfluid with exciton-polaritons.

A follow-up study on the two-states in the exciton-polariton superfluid reported in this article revealed that the two states occur sequentially and not concurrently. The apparent coexistence of the two states, thus, is not due to partial rotation of a superfluid. This new finding alters the conclusion of this article significantly so as to necessitate a withdrawal instead of an update