Photon anti-bunching

With individual photons, information can be safely encrypted by using their entangled quantum-states. Paulo Santos and coworkers developed a single-photon source which allows them to emit single photons with exact rate and very high repetition. They use surface acoustic waves to pump electrical charges across a semiconductor that is patterned with quantum-dots.

Although extensive research on nanostructures has led to the discovery of a number of efficient ways to confine carriers in reduced dimensions, little has been done to make use of the unique properties of various nanostructured systems through coupling by means of the controllable transfer of carriers between them. Here, a novel approach for the controllable transfer of electrons and holes between a semiconductor quantum well and an embedded quantum dot is demonstrated, using the moving piezoelectric potential modulation induced by an acoustic phonon. It is shown that this moving potential not only  transfers carriers between the quantum well and an array of quantum dots, but can also control their capture and recombination in discrete quantum dot states within the array. This feature is used to demonstrate a high-frequency, single- photon source with tunable emission energy by acoustically transferring carriers to a selected quantum dot.

Figure: A laser generates electrons and holes (arrow down). An acoustic wave pumps the charge carriers towards the quantum-dots leading to their excitation and the emission of a photon (arrow up).