Bose-Einstein Condensation of Long-lifetime Polaritons in Microcavities
Speaker: David Snoke, University of Pittsburgh
Department: Electrical Engineering
Location: Engineering Quadrangle J401
Date/Time: Wednesday, July 17, 2013, 2:00 p.m. - 3:00 p.m.
Polaritons are quasiparticles which arise as mixed states of photons and electronic excitations; in a microcavity these can be tuned to have very light mass (four orders of magnitude less than an electron) and relatively strong interactions. One can call them photons dressed with mass and hard-sphere interactions; as such, they obey the equations of bosonic atoms and can undergo Bose-Einstein condensation, but at much higher temperature. Until recently, polaritons in semiconductor microcavities had short lifetime so that they did not reach complete equilibrium. Our new samples, grown by the group of Loren Pfeiffer at Princeton, have world-record lifetimes. We have seen ballistic, coherent transport of the polaritons over hundreds of microns up to a millimeter, and we can also confine the polarition gas in a trap. We have seen that the trapped polariton gas can truly thermalize to the background bath temperature; from this we deduce the phase diagram for Bose condensation of the polariton gas, and show that the critical temperature increases linearly with increasing temperature, consistent with the prediction for a weakly interacting Bose gas. I will also discuss very recent results with ring trap for the polaritons, i.e., a Mexican-hat potential that allows circulation.