"Experimental realization of Wheeler's delayed-choice Gedanken Experiment"

We report an almost ideal realization of wheeler's "delayed-choice" experiment where the light pulses are true single photons, allowing unambiguous which-way measurements. The clock-triggered single-photon source at the heart of the experiment, previously developed for quantum key distribution, is based on the pulsed, optically excited photoluminescence of a single N-V colour centre in a diamond nanocrystal. This system, which consists in a substitutional nitrogen atom (N) associated to a vacancy (V) in an adjacent lattice site of the diamond crystalline matrix, has an unsurpassed efficiency and photostability at room temperature.