For a single semiconductor quantum dot embedded in a microcavity, we theoretically and experimentally investigate phonon-assisted transitions between excitons and the cavity mode. Within the framework of the independent boson model we find that such transitions can be very efficient, even for relatively large exciton-cavity detunings of several millielectron volts. Furthermore, we predict a strong detuning asymmetry for the exciton lifetime that vanishes for elevated lattice temperature. Our findings are corroborated by experiment, which turns out to be in good quantitative and qualitative agreement with theory

Nitrogen-vacancy (NV) centers in diamond are generally recognized as highly promising as indefinitely stable highly efficient single-photon sources. We report an experimental quantification of the brightness, radiative decay rate, nonradiative decay rate and quantum efficiency of single NV centers in diamond nanocrystals. Our experiments show that the commonly observed large spread in fluorescence decay rates of NV centers in nanodiamond is inconsistent with the common explanation of large nanophotonic mode-density variations in the ultra-small high-index crystals at near-unity quantum efficiency. We report that NV centers in 25 nm nanocrystals are essentially insensitive to local density of optical states (LDOS) variations that we induce at a dielectric interface by using liquids to vary the refractive index, and propose that quantum efficiencies in such nanocrystals are widely distributed between 0 and 20%. For single NV centers in larger 100 nm nanocrystals, we show that decay rate changes can be reversibly induced by nanomechanically approaching a mirror to change the LDOS. Using this scanning mirror method, for the first time we report calibrated quantum efficiencies of NV centers, and show that different but nominally identical nanocrystals have widely distributed quantum efficiencies between 10 and 90%. Our measurements imply that nanocrystals that are to be assembled into hybrid photonic structures for cavity QED should first be individually screened to assess fluorescence properties in detail.

Surface plasmon resonators can drastically redistribute incident light over different output wave vectors and polarizations. This can lead for instance to sub-diffraction sized nanoapertures in metal films that beam and to nanoparticle antennas that enable efficient conversion of photons between spatial modes, or helicity channels. We present a polarimetric Fourier microscope as a new experimental tool to completely characterize the angle-dependent polarization-resolved scattering of single nanostructures. Polarimetry allows determining the full Stokes parameters from just six Fourier images. The degree of polarization and the polarization ellipse are measured for each scattering direction collected by a high NA objective. We showcase the method on plasmonic bullseye antennas in a metal film, which are known to beam light efficiently. We find rich results for the polarization state of the beamed light, including complete conversion of input polarization from linear to circular and from one helicity to another. In addition to uncovering new physics for plasmonic groove antennas, the described technique projects to have a large impact in nanophotonics, in particular towards the investigation of a broad range of phenomena ranging from photon spin Hall effects, polarization to orbital angular momentum transfer and design of plasmon antennas.

We experimentally investigate the nonresonant ͑⌬E Ͼ 5 meV͒ feeding of photons into the optical mode of a two-dimensional photonic crystal nanocavity by quantum dot multiexciton transitions. Power-dependent photoluminescence measurements reveal a superlinear power dependence of the mode emission, indicating that the emission stems from multiexcitons. By monitoring the temporal evolution of the photoluminescence spectrum, we observe a clear anticorrelation of the mode and single exciton emission; the mode emission quenches as the population in the system reduces toward the single exciton level while the intensity of the mode emission tracks the multiexciton transitions. Our results lend strong support to a recently proposed mechanism ͓M. Winger et al., Phys. Rev. Lett. 103, 207403 ͑2009͔͒ mediating the strongly nonresonant feeding of photons into the cavity mode.Semiconductor quantum dots ͑QDs͒ exhibit atomlike properties such as a discrete interband optical spectrum with nearly homogeneously broadened transitions and shell filling effects as carriers ͑electrons and holes͒ are added. As a result, they are natural candidates for conducting cavity quantum electrodynamics ͑cQED͒ experiments in the solid state. 1 Among the many potential applications of single QD-cavity structures are the efficient and deterministic generation of indistinguishable photons, 2 devices that exploit single photon quantum nonlinearities, 3 and ultralow threshold nanolasers. 4 While exhibiting many properties known from atom based cQED, a number of surprising deviations from this model system have been identified. For example, recent experiments have revealed pronounced emission from the cavity mode, even when all the discrete QD emission lines are spectrally detuned. 5-7 This effect has been attributed to phonon mediated dot-cavity interactions for small dot-cavity detunings up to a few meV. 8-11 However, nonresonant QD-cavity coupling was also observed for much larger detunings, up to ϳ20 meV ͑Refs. 5, 7, 12, and 13͒ which cannot be attributed to phonon mediated processes. Experimental investigations of such highly nonresonant coupling revealed apparently contradictory observations in photon autocorrelation and crosscorrelation measurements: 5-7,12 ͑i͒ the QD emission is strongly antibunched, ͑ii͒ the cavity emission is Poissonian while ͑iii͒ pronounced crosscorrelations exist between the QD and cavity mode emission. Winger et al. explained these observations by a model that links the strong off-resonant cavity mode emission to Purcell enhanced decay into a quasicontinuum of few particle states. 12 The coexistence of the discrete QD states, where all particles are confined in the dot, and the quasicontinuum, where some particles occupy states in the wetting layer is inherent to the mesoscopic nature of the QD confinement.In this Rapid Communication, we present experimental investigations of cavity mode feeding from spectrally detuned QD multiexciton states for a wide range of negative and positive single exciton-mode detunings ͑ QD − cav =...