  We demonstrate condensation of microcavity polaritons with a very sharp
threshold occuring at two orders of magnitude lower pump intensity than
previous demonstrations of condensation. The long cavity-lifetime and trapping
and pumping geometries are crucial to the realization of this low threshold.
Polariton condensation, or "polariton lasing" has long been proposed as a
promising source of coherent light at lower threshold than traditional lasing,
and these results suggest methods to bring this threshold even lower.
