Quantum Secure Direct Communication Using EPR Entangled Photon Pair As Quantum Channel

Quantum cryptography is a new crossing subject developed in the recent twenty years, which is the combination of quantum theory, information science and computer science. Quantum cryptography, which is based on classical cryptography and quantum mechanics, is a new type of cryptographic system which utilizes quantum domino offect to transmit information unconditionally securely. Compared with traditional cryptography based on mathematics complexity, quantum cryptography is absolutely secure in theory, so it has a widely applied foreground and greatly scientific significance today where information intercourse is more and more frequent. As an important branch of quantum cryptography, quantum secure direct communication (QSDC) can transmit secret information directly without first establishing a random key to encrypt them between two communication parties. QSDC is the phenomenon only emerged in quantum mechanics, and takes greatly important role in the progress of quantum information processing and provides a new physics resource for information transmission and information processing. Exploiting and utilizing these new resource is an important motivation of quantum cryptography research. Using EPR pair as quantum channel, we design several QSDC schemes as follow:1. A quantum secure direct quantum communication protocol was presented, in which the photons carrying secret message is not sent in the public channel.2. A quantum secure direct quantum communication protocol based on nonorthogonal entangled photon pair and local measurement was presented. The scheme can validly resist all kinds of intercept-resend attack and entangle-measure attack by utilizing the nonorthogonality between entangled photon pairs.3. A quantum secure direct quantum communication protocol based on local measurement and one time pad is presented, which can validly detect Eve's attack action hiding in the channel loss.4. by lucubrating all kinds of the encoding scheme, we present a quantum secure direct quantum communication protocol in which channel capacity is improved.