Quantum cryptography device and method

Interferometric system configured for the distribution of a key over a quantum channel using quantum cryptography, comprising:

• at least one sending/receiving station and at least one key encoding station, both coupled to said quantum channel,
• means in at least one of said stations for sending at least two light pulses over said quantum channel to at least one other said station,
• detectors in at least one of said stations for detecting interference created by said pulses in said stations,
• wherein said light pulses traverse the same branches of the interferometric system, each of said pulses traversing the same branches in a different sequence so that said pulses are delayed when traversing said quantum channel.

Key encoding station for communicating a key to at least one sending/receiving station through a quantum channel comprising:

• reflecting means for reflecting a first pulse sent by a receiving station back to said receiving station;
• reflecting means for reflecting a second pulse, sent by said receiving station shortly after said first pulse, back to said receiving station;
• and
• modulating means for modulating the phase of said second pulse with respect to said first pulse.

Sending/receiving station for receiving a key sent from one key encoding station through a quantum channel, comprising:

• a pulsed laser source;
• a delay line;
• detecting means;
• and
• a first coupler connected in such a way that the pulses emitted by said pulsed laser source are split in two pulses;
• wherein said delay line is configured such that a first split pulse is directly sent to said quantum channel and a second split pulse is delayed by said delay line before being sent to said quantum channel;
• and
• wherein the pulses received from said quantum channel are split in two pulses, the first pulse being directly sent to said detecting means and the second pulse being delayed by said delay line before being sent to said detecting means.