  We report that hybridizing semiconductor quantum dots with plasmonic
metamaterial leads to a multi-fold intensity increase and narrowing of their
photoluminescence spectrum. The luminescence enhancement is a clear
manifestation of the cavity quantum electrodynamics Purcell effect that can be
controlled by the metamaterial's design. This observation is an essential step
towards understanding loss compensation in metamaterials with gain media and
for developing metamaterial-enhanced gain media.
