Single or Entangled Photon Source

Electrically triggered single or entangled photon sources are needed for high security quantum cryptography. In addition, the mass market requires efficient electrically driven high-speed devices. Common growth and processing techniques are used to fabricate single photon sources, which either generate polarization entangled photon pairs or polarization controlled single photons. This offers great opportunities to use single photons or entangled photon pairs for quantum cryptography.

We offer a method for producing a single or an entangled photon source which can be provided in a simple and reproducible manner. This novel method enables the production of a compact single photon source which can alternatively emit defined linearly polarized single photons, transposed photon pairs or cascades of correlated photons. The fine structure splitting of the exciton energy level of a quantum dot (QD) depends on material strains. The result ot the invention was to selectively establish the degree of strain within the quantum dots and within the surrounding material structure by the choice of the size of the QD.