METHOD AND DEVICE FOR PRODUCING A CHOICE OF EITHER SINGLE PHOTONS OR PAIRS OF PHOTONS IN AN OPTICAL CHANNEL

摘要

The invention relates to a method for producing a choice of either single photons or pairs of photons in an optical channel (16, 17), comprising the following steps: establishing a two-photon state (photon pair); physically separating said photon pair and obtaining the quantum mechanical correlation in the event that the photons are emitted collinearly; coupling each photon into one optical channel (14, 14', 14") respectively, one channel (15, 15', 15") containing an interferometer (7-13) with a variable difference in optical paths delta 1F- delta 1S and the other channel containing an optical retardation route (19) of optical length delta 1; physically bringing the two channels together with a beam splitter (18, 31-36); matching the values delta 1F, delta 1S and delta 1 in such a way that the probability K of coincidences between the outputs (16, 17) of the beam splitter can be either approximately K=0 or approximately K=1 or approximately a predetermined intermediate value, K=0 corresponding to a photon pair in one of the output channels (16, 17) of the beam splitter and K=1 corresponding to two single photons in the two output channels of the beam splitter. The invention provides a means of producing an optical separating filter or gate for either single photons or photon pairs which can be used in quantum cryptography and as a basic element of a quantum optical calculating machine.