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<div><font face="Arial" color="#000000">Seminar on<br>
<b>Modern Optics and Spectroscopy<br>
<br>
<br>
David Snoke</b>,<br>
University of Pittsburgh<br>
<br>
<i><b>Bose-Einstein condensation of polaritons in microcavities<br>
<br>
</b></i>October 2, 2007<br>
<br>
12:00 - 1:00 p.m.</font></div>
<div><font face="Arial" color="#000000">Grier Room 34-401<br>
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<br>
</font><font color="#000000">Polaritons are bosonic quasiparticles
which are a superposition of photons and excitons in a solid. In
microcavity structures, they have effective mass and a repulsive
interaction, and can move freely in a two-dimensional plane, so that
they can be treated as a weakly interacting Bose gas. We have
recently demonstrated (Science<b> 316</b>, 1007 (2007)) trapping of
polaritons in a harmonic potential; under these conditions the
polaritons show a number of effects associated with Bose-Einstein
condensation: a bimodal momentum distribution, a spatial condensation
in the center of the trap, spontaneous symmetry breaking as seen in
polarization of the emitted light, and long-range coherence as seen in
intererence patterns of the emitted light. Although the polaritons
exist for only a few picoseconds, the analogy with a weakly
interacting atomic gas is good, and the effects of incomplete
equilibrium do not destroy the condensate completely.</font></div>
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