Quantum amplifiers, quantum duplicators and quantum cryptography
Horace P. Yuen · Quantum and Semiclassical Optics Journal of the European Optical Society Part B · 1996
Several methods for eavesdropping on the standard four coherent-state quantum cryptosystem together with a possible countermeasure are analysed and found to place a limit on the tolerable energy disadvantage of the users as compared to the eavesdropper. The possible significant role of the photon-number amplifier and the photon-number duplicator is indicated.