Triggered single photons from a quantum dot

Summary form only given. A source of single photons, each arriving within a known time interval, would be useful in the new field of quantum cryptography, where security from eavesdropping requires that only one photon be sent at a time. While other recent efforts to generate single photons have relied on saturated absorption in a single quantum emitter such as a molecule our method takes advantage of the emission properties of a single emitter, an InAs dot. When a laser pulse creates multiple electron-hole pairs (excitons), the last pair to recombine creates a photon at a unique wavelength, which can be spectrally separated from the others. This is because Coulomb interactions shift the emission wavelength when multiple excitons are present.