A highly efficient two level diamond based single photon source

An unexplored diamond defect center that is found to emit stable single photons at a measured rate of 1.6 MHz at room temperature is reported. The center, identified in chemical vapor deposition grown diamond crystals, exhibits a sharp zero phonon line at 734 nm with a full width at half maximum of ?4 nm. The photon statistics confirm that the center is a single emitter and provides direct evidence of a true two level single quantum system in diamond