Patent ID: 8306225

Claim:
A quantum communication system comprising: an emitter and a receiver, said emitter comprising an encoder and at least one photon source, a separator for dividing photon pulses emitted from said photon source into a signal pulse and a reference pulse, wherein the reference pulse is delayed by a predetermined time after the signal pulse and the reference pulse is encoded in a different manner from the signal pulse; said emitter configured to pass a signal pulse and a reference pulse, which are separated in time, through a same path in said encoder and output the signal pulse and the reference pulse, wherein the average number of photons per signal pulse is less than one photon and the average number of photons per reference pulse is greater than the average number of photons per signal pulse, the signal and reference pulses being separated in time prior to entry into said encoder, said receiver comprising a decoder and at least one detector for measuring said signal pulse and said reference pulse, wherein the receiver is configured to measure the reference pulse and the signal pulse at separate times and based on the measured reference pulse to determine phase or polarization drift in the quantum communication system; wherein the receiver further comprises a feedback circuit configured to alter a component of the receiver on the basis of a measured reference signal; and wherein the receiver further comprises gating configured to keep the detector in an on mode only for the time the detector expects to receive the signal pulse or the reference pulse.