Clemens Matthiesen and co-workers from the University of Cambridge and the University of Rochester have reported the emission of highly coherent (sub-natural linewidth) single photons from InAs quantum dots. The researchers used a confocal microscope to collect optically excited resonant fluorescent spectra at a temperature of 4 K. The InAs quantum dots were embedded in a Schottky diode heterostructure, which allowed their excitonic energy levels to be tuned through the d.c. Stark effect. To combine the processes of absorption and emission into a single coherent event, the researchers decreased the excitation power so that the Rabi frequency was less than a fifth of the spontaneous emission rate. Strong antibunching in the intensity-correlation measurement suggests that the generated photons were non-classical in nature. The researchers measured a coherence time of 22 ns — 30 times longer than the lifetime of the quantum dot transition — through field-correlation measurements using a Michelson interferometer. The single photons exhibited a linewidth of 7 MHz, which is a metric inherited from the excitation laser.
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Horiuchi, N. Superior single photons. Nature Photon 6, 268 (2012). https://doi.org/10.1038/nphoton.2012.94
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DOI: https://doi.org/10.1038/nphoton.2012.94