Vortices and anti-vortices

Project overview

Topological defects occur in many areas of science, including particle physics, cosmology, condensed matter physics and optics. Vortices are typical examples, which occur in bosonic condensates, such as dilute gases, liquid helium, superconductors and polariton BECs.

We observed spontaneous vortex formation in the microcavity optical parametric oscillator (OPO) carrying finite orbital angular momentum (OAM). We also demonstrate that a weak probe beam carrying OAM enables imprinting of a vortex state on to macroscopically occupied polariton states.

The OPO was excited using a laser beam without OAM. Figure (a) below shows an image of the ‘signal’ emission at k=0 in real space above threshold. At the edge of the emission a defect is formed with a dip in the emission intensity (region A).

Figure (b) shows the interference pattern between the ‘signal’ image in (a) and the same image inverted in so that region A is mixed with region B. The fork-like dislocation indicates the spontaneous formation of a quantised vortex with finite OAM (L=1) in the signal.

The phase relationship between pump, signal and idler results also in an anti-vortex in the idler state of OAM L=-1.