The invention relates to the distribution of a cryptographic key using weak light pulses generated by a laser or generated by a source of entangled photon pairs.
In both schemes, for both prepare and measure protocols (such as BB84) and entangled-based protocols such as E91, it is possible to send more than one key bit per registered photon, thus increasing the speed of cryptographic key generation even in the presence of high optical signal losses in the transmission channel.
Thanks to the possibility of independently encoding multiple qubits using a single photon and utilizing the phenomenon of interference occurring in active receivers, the security of each of the proposed schemes is analogous to BB84 and/or E91 protocols, etc., in which only one qubit is transmitted using a single photon.
