Observation of room-temperature spontaneous superradiance from single   diamond nanocrystals
  We report the observation of room-temperature superradiance from single, highly luminescent diamond nanocrystals with spatial dimensions much smaller than the wavelength of light, and each containing a large number (~10^3) of embedded nitrogen-vacancy (NV) centres. After excitation of the nanodiamonds with an off-resonant, green laser pulse, we observe i) ultrafast radiative lifetimes down to ~ 1 ns, and ii) super-Poissonian photon bunching in the autocorrelation function of the light emitted from the fastest nanodiamonds. We explain our findings with a detailed theoretical model based on collective Dicke states and well-known properties of NV centres. Using a minimal set of fit parameters, the model captures both the wide range of different lifetimes and the nontrivial photon correlations found in the experiments. The results pave the way towards a systematic study of superradiance in a well controlled, solid-state quantum system at room temperature. Ultimately, quantum engineering of superradiance in diamond has the potential for advancing applications in quantum sensing, energy harvesting, and efficient photon detection. 
Carlo Bradac, Mattias Johnsson, Matthew van Breugel, Ben Baragiola,   Rochelle Martin, Mathieu L. Juan, Gavin Brennen, and T...
quant-ph cond-mat.mes-hall