| Abstract: | A new family of two-parameter quantum key distribution protocols is discussed where eavesdropping is detected by using two
parameters: bit error rate Q and photon count rate q in control time slots. When a single-photon source is used and mutually orthogonal states are prepared in each basis, the
protocol’s maximum tolerable error rate for secure key distribution is the highest, reaching a theoretical upper limit of
50%. When the signal states emitted by the source of attenuated laser light include multiphoton coherent states, the protocol
also guarantees secure key distribution over the longest distance as compared to other quantum cryptography systems, up to
the channel length for which the channel losses are sufficiently high that all five-photon pulses can be blocked by an eavesdropper. |
