System and method of entangled photons generation

Apparatus for producing quantum correlated and/or entangled photon pairs, said apparatus comprising:

• a source of a plurality of photons;
• the source connected to a polarization maintaining optical circulator followed by
• a polarization switch and then a differential polarization group delay element;
• the polarization switch operating in a first and second position;
• in the first position the source photons are split evenly into photons with both polarization axes of the differential polarization group delay element and in the second position the source photons are aligned to one polarization axis of the delay element;
• the output of the delay element being coupled into a nonlinear fiber producing signal and idler photons through a four-wave mixing interaction, the nonlinear fiber being coupled to a non-reciprocal reflector causing the photons to be retro-reflected back through the nonlinear fiber and the group delay element, the reflected photons being collected by the polarization maintaining circulator to produce output photons, said output photons being in an entangled state if the polarization switch is in the first position and a quantum correlated state if the polarization switch is in the second position.

Apparatus for producing quantum correlated and/or entangled photon pairs, said apparatus comprising:

• a source of a plurality of photons;
• the source connected to a polarization controller followed by an optical circulator and then a differential polarization group delay element;
• the output of the delay element being connected to a coupler with two output ports, wherein one output port is connected to a monitor that measures information about the monitor optical input signal, said monitor sending the information to a feedback control element that uses a polarization information to adjust the polarization controller to either measure a single polarization at the monitor or an unpolarized signal at the monitor and wherein the other coupler output port is connected to a nonlinear fiber, wherein four-wave mixing in the nonlinear fiber generates signal and idler photons, said nonlinear fiber being connected to a non-reciprocal reflector such that after the photons are retro-reflected back through the nonlinear fiber and the polarization differential group delay element, the reflected photons being collected by the circulator to produce output photons, said output photons being in an entangled state if the feedback control element configures the polarization controller in the way that an unpolarized state is measured at the monitor or in a polarized quantum correlated state if the feedback control element configures the polarization controller in the way that a polarized state is measured at the monitor.

Method for producing entangled photon pairs, said method comprising:

• generating a plurality of photons in a source photons;
• coupling the source photons into a polarization maintaining optical circulator followed by a polarization switch and then a differential polarization group delay element;
• switching the polarization switch between a first and second position;
• in the first position the source photons being split evenly into photons with both polarization axes of the delay element and in the second position the source photons having one polarization axis of the delay element;
• coupling the output of the delay element into a nonlinear fiber producing signal and idler photons through a four-wave mixing interaction, reflecting an output signal from the nonlinear fiber by a non-reciprocal reflector causing the photons being'retro-reflected back through the nonlinear fiber and the delay element, collecting the reflected photons by the polarization maintaining circulator to produce output photons, wherein said output photons being in an entangled state if the polarization switch is in the first position and a quantum correlated state if the polarization switch is in the second position.