  By modifying the density of optical states at the location of an emitter,
weak cavity-emitter coupling can enable a host of potential applications in
quantum optics, from the development of low- threshold lasers to brighter
single-photon sources for quantum cryptography. Although some of the first
demonstrations of spontaneous emission modification occurred in metallic
structures, it was only after the recent demonstration of cavity quantum
electrodynamics effects in dielectric optical cavities that metal-based optical
cavities were considered for quantum optics applications. Advantages of
metal-optical cavities include their compatibility with a large variety of
emitters and their broadband cavity spectra, which enable enhancement of
spectrally-broad emitters. Here, we demonstrate a metal- based nanocavity
structure that achieves radiative emission rate enhancements of 1000, opening
up the possibility of pursuing cavity electrodynamics investigations with
intrinsically broad optical emitters, including organic dyes and colloidal
quantum dots.
