Method for all-optical passive decoy-state quantum key distribution

It is claimed a method for decoy state quantum key generation comprising the steps, preferably in this order,i) generation of at least two sequences of laser pulses by a pulse generation means (2);ii) conversion of the at least two sequences of laser pulses into at least two sequences of pulses with random phase by a phase generation means (3), whereby each pulse of each sequence has a random phase;iii) conversion of the sequences of pulses with random phase into one or more sequences of pulses with random phase and an additional degree of freedom in a conversion means (4);iv) combination of at least two pulses of the one or more sequences of pulses with random phase and the additional degree of freedom to generate a decoy state, and continue the combination for subsequent pulses in order to generate a sequence of pulses comprising decoy states. According to the invention, the combination in step iv) is an interference of the at least two pulses in an interference means (5).