Tham khảo tài liệu 'optical fiber communications and devicesan incorrectly part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Secure Long-Distance Quantum Communication over Optical Fiber Quantum Channels 165 state which provides information to the eavesdropper without any disturbance. The DPS protocol is robust against such photon number splitting attacks in practice however a theoretical lower bound on the security of the protocol is still missing from the literature Inoue et al. 2003 Honjo et al. 2004 . The working mechanism of the DPS QKD protocol is based on the same idea as the B92 protocol Bennett 1992 even two non-orthogonal quantum states are sufficient to perform a secure quantum key distribution. In the DPS protocol Alice encodes the logical bits in the phase of the pulses. If the phases are modulated by 0 then Alice sends a logical zero and if the phase between the two pulses is t then she encodes a logical one. If the relative phase between two pulses is 0 then Bob will detect 0 and similarly if the phase between the two pulses is t then he will obtain a logical 1. In the sending process Alice generates coherent states of the same intensity ỊL and from these states she forms a sequence as follows Y . e T I e 4 j J . . k -1 k k 1 . 1 where the phases can be set at 0 or t hence for a logical zero we have e efk 1 and for a logical one the difference between the two phases is t and e n e Vk 1 . Since the logical bits are encoded in the phases between the signals the k -th signal has relevance in the determination of both the k -th and k 1 -th logical bits hence I . y k -1 k k 1 . and this fact increases the complexity of any security analysis Inoue et al. 2003 Honjo et al. 2004 . From this viewpoint the DPS protocol has been analyzed by Takesue et al. Takesue et al. 2005 . In this section we show that the complexity of the DPS QKD protocol s security analysis can be decreased dramatically using fast computational information geometric methods Gyongyosi Imre 2010 Gyongyosi Imre 2010a Nielsen et al. 2007 Nielsen Nock 2008 Nielsen Nock 2008a Nielsen Nock 2009 . The security of the .
