Quantum key distribution with time coding on linearly dependent states.

A quantum key distribution protocol with information coding by the time of photon arrival based on four linearly dependent single-photon states is proposed and the resistance of the protocol to a realistic intercept-resend attack is analyzed. The protocol on four linearly independent states is shown to be sensitive to an attack with unambiguous discrimination of all states when the level of losses in the quantum channel is higher than 7.2 dB. [ABSTRACT FROM AUTHOR]