Deutschetelekom Ag

Helmar A Becker

Wolfgang Dultz

Heidrun Schmitzer

Gisela Dultz

Kay Michael Schmid

A method is provided for changing the polarization of at least one of the photons emitted from a photon pair source into various partial ray paths using an electro-optical modulator (EOM), which is positioned in the particular partial ray path being traversed by the photon to be influenced and which, in the activated state, is able to alter the polarization of a photon, the modulator being activated as a function of time such that the probability that the photon is found in the region of the electro-optical modulator in the activated state is at a maximum.

METHOD FOR CHANGING THE POLARIZATION OF AT LEAST ONE OF THE PHOTONS EMITTED FROM A PHOTON-PAIR SOURCE INTO VARIOUS PARTIAL PATHS OF RAYS, AND METHOD FOR OPTIONALLY GENERATING INDIVIDUAL PHOTONS OR PHOTON PAIRS IN AN OPTICAL CHANNEL

A method and device for generating a choice of individual photons or photon pairs in an optical channel. The generation of this choice involves generating a two-photon state corresponding to a photon pair and spatially separating the photon pair while preserving the quantum-mechanical correlation, in the event the photons are emitted in a collinear manner. One photon is coupled into one optical channel each, the one channel containing an interferometer with variable optical path-length difference &dgr; , and the other channel including an optical delay section having the optical length &dgr; The channels are spatially reunited through a beam splitter, and an adjustment of the quantities &dgr; , and &dgr; occurs in such a way that the probability K for coincidences between the outputs of the beam splitter is a choice of approximately K&equals;0 or approximately K&equals;1, or approximately a predetermined intermediate value, with K&equals;0 corresponding to a photon pair in one of the output channels of the beam splitter, and K&equals;1 corresponding to two individual photons in both output channels of the beam splitter. With this choice generation, an optical separating filter or gate can be implemented for a choice of one-photon or two-photon states, which is usable in quantum cryptography and as a basic element of a quantum-optical computing machine.

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Hanau, Germany

Helmar A Becker