Quantised Vortices in an Exciton-Polariton Fluid

TL;DR

This paper reports the observation of quantized vortices in a Bose-Einstein condensate of exciton-polaritons, providing evidence for superfluidity in a solid-state, non-equilibrium quantum fluid, supported by phase imaging and theoretical modeling.

Contribution

It presents the first direct observation of pinned quantized vortices in a polariton condensate, advancing understanding of superfluidity in solid-state systems.

Findings

Observation of spontaneous quantized vortices in polariton BEC

Vortices are pinned and stable, indicating superfluid behavior

Theoretical analysis supports superfluidity in non-equilibrium polariton fluids

Abstract

One of the most striking quantum effects in a low temperature interacting Bose gas is superfluidity. First observed in liquid 4He, this phenomenon has been intensively studied in a variety of systems for its amazing features such as the persistence of superflows and the quantization of the angular momentum of vortices. The achievement of Bose-Einstein condensation (BEC) in dilute atomic gases provided an exceptional opportunity to observe and study superfluidity in an extremely clean and controlled environment. In the solid state, Bose-Einstein condensation of exciton polaritons has now been reported several times. Polaritons are strongly interacting light-matter quasi-particles, naturally occurring in semiconductor microcavities in the strong coupling regime and constitute a very interesting example of composite bosons. Even though pioneering experiments have recently addressed the propagation of a fluid of coherent polaritons, still no conclusive evidence is yet available of its superfluid nature. In the present Letter, we report the observation of spontaneous formation of pinned quantised vortices in the Bose-condensed phase of a polariton fluid by means of phase and amplitude imaging. Theoretical insight into the possible origin of such vortices is presented in terms of a generalised Gross-Pitaevskii equation. The implications of our observations concerning the superfluid nature of the non-equilibrium polariton fluid are finally discussed.