Efficient fault-tolerant quantum dialogue protocols using a quantum reordering circuit of EPR pairs

This study proposes two efficient fault-tolerant quantum dialogue (QD) protocols that are robust against the collective-dephasing and collective-rotation noises, respectively. In the proposed protocol, the message carriers are decoherence-free quantum states that are resistant to the corresponding collective noise, provided that all quantum photon pairs of a transmitted unit remain within the same time window. These quantum states and their combinations are used to compose the decoy photon pairs to ensure the security of the transmission. An observation on the Bell measurement has allowed an EPR pair as a message carrier to Require only one of its photons for protection. That is, the measurement of one single photon in an EPR pair will gain no information on its actual Bell state. This property has effectively reduced the number of decoy photons in quantum transmission. Since the photons used in the message carriers are particles of EPR pairs, the proposed two fault-tolerant QD protocols required only half of the decoy photons to ensure the same level of security. In the transmission, one photon of each EPR pair is separated using a reordering mechanism, and a quantum logic circuit is designed and implemented to demonstrate the concept in practice. The reduction of decoy photons has significantly improved the qubit efficiency of the proposed QD protocols compared with other relevant existing works. Furthermore, the proposed schemes also have no information leakage problem.