Quantum cryptography transmission method and system

Digital data encoder for use by a signal transmitter on particle flow such that the probability of transmitting two particles per period is negligible, wherein it can be used at least to convert the sequency of K bits of digital data into a train of K pulses of particle of time width ΔT and whose frequency Tb, is predetermined knowing that each of the K pulses being shifted or not in time such that the kth pulse is shifted by a duration t0 respectively t1, with respect to the initial instant of the period depending on the value “0”, respectively “1” of the kth bit, where k is an integer such that 0≦k<K and the shifts t0 and t1 are such that 0≦t0,t1≦Tb−ΔT and 0≦It1−t0I<ΔT.

Encoder according to the previous claim, wherein it comprises at least:

• a device (11), called continuous source, generating a continuous particle flow,
• a device (12), called pulse chopper, chopping a train of pulses of time width ΔT and frequency Tb in the continuous particle flow, and
• a device (13), called delay gate, shifting the pulses chopped in the particle flow to match the values of the bits to be encoded.

Decoding method according to the previous claim, wherein, when the time width ΔT and the spectral width Δv of the pulses used by the encoding method satisfy the following relation:

• Δv.ΔT=1, it comprises one or more of the following steps:
• a filtering step which only allows the particles of spectral width Δv to pass, carried out upstream from observation and detection;
• a count of the number NΔf, of particles received of spectral width equal to Δv, a count of the number NΔf of particles received of different spectral width Δf (Δf≠Δv) and a comparison of these two numbers NΔv and NΔf such that if NΔv<<NΔf, the interception of particles by a third party is indicated.

Decoder according to the previous claim, wherein it comprises at least a first particle counter (31′) which only counts the particles present in the observation window(s) and/or wherein, when the time width ΔT and the spectral width Δv of the pulses used by the encoder (1) satisfy the following relation:

• Δv.ΔT=1, it also comprises one or more of the following devices:
• a filter which only allows the particles of spectral width Δv to pass to the first particle counter;
• the first particle counter (31′) generating the number NΔv, of particles it detects, a second counter (31″) generating the number NΔf of particles received by the decoder (3) and of spectral width Af different from Δf≠Δv, a comparator (32) of these two numbers NΔv, and NΔf such that if NΔv<<NΔf, it generates a predetermined signal indicating either ambiguity of the bit value or interception of particles by a third party.