Unambiguous State Discrimination of Coherent States with Linear Optics: Application to Quantum Cryptography

摘要: We discuss several methods for unambiguous state discrimination of N symmetric coherent states using linear optics and photodetectors. One type measurement is shown to be optimal in the limit small photon numbers any N. For special case $N=4$ this can fruitfully used by receiving end (Bob) an implementation Bennett-Brassard 1984 (BB84) quantum key distribution protocol faint laser pulses. In particular, if Bob detects only a single procedure equivalent standard that he would have perform single-photon BB84, two photons will unambiguously know bit sent him 50% cases without having exchange basis information, three are detected, which was sent.