Bose-Einstein Condensation of Microcavity Exciton-Polaritons
The Waterloo Institute for Nanotechnology (WIN) is pleased to invite you to Coffee and Connection with our executive director Sushanta Mitra with a guest speaker Hassan Alnatah a PhD candidate at the University of Pittsburgh.
This seminar is titled "Bose-Einstein Condensation of Microcavity Exciton-Polaritons" and will be held on Thursday, August 17, 2023 at 3:30 PM in QNC 1501. Registration is not required!
I will first give a general introduction to exciton-polaritons. In the first part of my talk, I will discuss our results on the coherent fraction of a homogenous polariton gas in thermal equilibrium. We have measured the distribution function of a homogenous polariton gas near resonance and shown that it is well described by a Bose-Einstein distribution, indicating that the polariton gas is in thermal equilibrium (Fig. 1). Although condensate fraction of a strongly interacting Bose gas case has been studied extensively in helium-4 via superfluidity measurements, this has been much harder to do in the weakly interacting Bose gas (WIBG) limit with cold atoms. Therefore, a verification of WIBG theory would be of real interest. Our system allows us to directly measure the coherence of the polariton gas by creating the interference pattern of the light emitted from the gas overlapped with its mirror image. Figure 2 shows the coherent fraction of the polaritons as a function of their density. This allows comparison of our results with theoretical predictions of the coherent fraction of an interacting 2D Bose gas.
In the second part of my talk, I will discuss our results on the persistent circulation of a polariton fluid. Persistent circulation is a canonical effect of superfluidity. We directly observe quantized circulation of a polariton condensate in a well-controlled steady state. We can cause the condensate to circulate in either direction on demand using a short laser pulse. Figure 3 shows the interference images of the condensate in a Mexican-hat trap with its mirror image. The different number of fringes on the top and the bottom implies the circulation of the condensate. Surprisingly, we find that the time scale of the persistence is extremely long compared to the pulse that stimulates the circulation, suggesting that the condensate is robust to many-body interactions.