Thales

Le Centre National De La Recherche

Rosa Tualle-Brouri

Thierry Debuisschert

Jerome Lodewyck

A continuous variable quantum encryption key distribution system comprises a sender (Alice) able 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, and to transmit to a receiver (Bob) the signal pulses (S) and a local oscillator (LO), the receiver comprising a homodyne detector () for measuring a randomly chosen quadrature of a signal pulse. The sender comprises a device for time-division multiplexing the pulses of the signal (S) and of the local oscillator (LO) to handle the transmission over an optical fiber () of the signal and local oscillator pulses to the receiver. The receiver comprises a demultiplexer (), able to send the received pulses over a first channel (), or over a second channel (). The channels are applied as inputs to the homodyne detector (). One of the first and second channels includes a phase modulator (), 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. A delay line (), is used for resynchronizing the signal and local oscillator pulses.

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Rosa Tualle-Brouri