Patent ID: 7894604

Claim:
A quantum cryptographic communication apparatus, comprising: a quantum communication path for transferring a quantum; a quantum transmitter apparatus provided on a transmission side of the quantum transfer path; a quantum receiver apparatus provided on a reception side of the quantum transfer path; and a control signal communication path connecting the quantum transmitter apparatus with the quantum receiver apparatus, the control signal communication path being used for communicating a control signal containing a synchronization signal between the quantum transmitter apparatus and the quantum receiver apparatus, and in that: a quantum receiver apparatus comprises: a light source serving as a quantum source; an optical path loop including a multiplexing/interfering means for generating time difference twin photon pulses composed of both a signal optical pulse and a reference optical pulse from a photon pulse outputted from the light source and for multiplexing and causing interference between the signal optical pulse corresponding to a retrograde quantum and the reference optical pulse; a bypass optical path including a phase modulator which is provided at a port connected to the quantum communication path, and phase-modulates only the reference optical pulse received after the time difference twin photon pulses are reciprocated via the quantum communication path between the quantum transmitter apparatus and the quantum receiver apparatus; and a photon detector for monitoring interference light passed through the optical path loop; the quantum transmitter apparatus comprises: a polarized wave rotating means for rotating polarization planes of the twin photon pulses at a right angle in a non-reciprocal manner, the twin photon pulses having reached thereto from the quantum receiver apparatus via the quantum communication path; a phase modulator for phase-modulating a signal optical pulse passes through the polarized wave rotating means and returning the signal optical pulse to the quantum receiver apparatus through the quantum communication path so as to return the phase-modulated signal optical pulse to the quantum receiver apparatus; and a beam attenuating means for attenuating the signal optical pulse such that the signal optical pulse includes less than two photons in the pulse.