Photon antibunching in double quantum ring structures

We address the question whether a quantum ring nanostructure can be considered as a single-photon emitter by means of intensity time-correlation measurement based on a Hanbury-Brown and Twiss interferometer. The second-order correlation function ${g}^{(2)}$ well characterizes the quantum nature of the emitter by the photon antibunching dip at zero delay. In concentric quantum rings we find evidence that the inner ring satisfies the requirement of single-photon source, while in the outer ring this requirement is relaxed.