Patent ID: 7929700

Claim:
A continuous variable quantum encryption key distribution system, comprising: a sender configured to randomly choose the phase and the amplitude of each coherent light pulse of a signal, to provide a coherent state defined by a first quadrature and a second quadrature that are random; a local oscillator configured to generate local oscillator pulses serving as a phase reference relative to which the phase of the signal is defined, the local oscillator pulses being great compared to the signal pulses; and a receiver for receiving signal pulses from said sender and including a homodyne detector for performing a measurement limited by the quantum noise to measure a randomly chosen quadrature of a signal pulse, wherein the sender comprises a time-division multiplexer for multiplexing transmission of the signal and the local oscillator pulses with a predetermined time interval between successive transmission of the signal and the local oscillator pulses over an optical fiber to the receiver; and wherein the receiver further comprises: a demultiplexer configured, to send the received pulses over a first channel, or over a second channel, said channels being applied as inputs to the homodyne detector; one of said first and second channels comprising: a phase modulator for enabling a random selection, by the homodyne detector, of a quadrature from the first and the second quadratures of a coherent state of a signal pulse; and a delay line for resynchronizing the received signal and local oscillator pulses between the first and second channels, the delay line being calibrated to impose a time delay that is equal to the predetermined time interval.