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2.Quantum Dialogue Protocol Using four-Photon W State

The four-photon W states can be rewritten as:

(iii) The first security checking phase

Aware of Bob’s confirmation that he has received 4-sequence, Alice tells him the position and the state of the checking qubits. Bob performs his measurement under the corresponding measurement bases as that chosen by Alice on the corresponding photons in his checking groups and compares the measurement outcome. If his measurement outcome is corresponding with the state that Alice sends to him, they confirm there is no eavesdropping in line. This communication continues. In this case, Alice and Bob continue to transmit the next bits.Otherwise, they have to discard their transmission and abort the communication. they abandon and start from step (i). In a noisy channel, Alice and Bob trust the quantum channel if the error rate is lower than that induced by noise.

3 The Security of this Protocol

In this paper we would not try to find subtle strategies to attack protocols, and the main topic focuses on the problem of information leakage, which implies that Eve can elicit some information about the secrets without any active attack(note that Eve just obtain information from the public annunciation and, as a result, it cannot be discovered by any detection). Therefore, we need not discuss the process of eavesdropping detection. We would pay our main attention to the process of message transmission. For example, suppose the measurement result is

4 Discussion and Conclusion

In conclusion, we have proposed a new quantum dialogue protocol for two legitimate parties to exchange their secret messages simultaneously by using four-photon W state. The result shows that, for such a four-photon W state quantum channel, a quantum dialogue can be realized between two users successfully. Compared with previous schemes, there are some differences in scheme proposed in this paper. Firstly, Quantum dialogue is the same as QKD and OTP (one time pad) communication, where the key of OTP is used twice. The key in OTP can never be reused, otherwise it would result in insecure.[26,27] However, the key of OTP is used twice simultaneously in quantum dialogue. That is to say, Alice and Bob decode the secret message in the same time after Alice announces her measurement outcome. So the quantum dialogue is secure. Secondly, In this paper, two different methods of analysis that Eve can obtain half of the information about Alice and Bob’s secret message by the classical channel,the result are the same.

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作者簡介：王東，生于1986年，畢業于西安工程大學，現在讀西安郵電學院通信與信息工程學院研究生，主要從事量子通信方面的研究。

作者簡介：柴旭超，生于1985年，畢業于西北工業大學，現就讀西安郵電學院通信與信息工程學院研究生，主要從事無線傳感器網絡等通信領域的研究。