Assuming there is a shared string between the users, we present a novel scheme, the lengthened string scheme (LSS), where the shared string is lengthened firstly by a specially designed algorithm, then some special treatments are applied on the lengthened one before it is used to authenticate. Based on the lengthened string scheme (LSS) we propose a quantum authentication protocol using entanglements. And the robustness of our protocol is discussed. In fact all the quantum key distribution protocols can do identification simultaneously based on the LSS.
GUO Fen-zhuo~(1,2), WEN Qiao-yan~1, ZHU Fu-chen~3 1.School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, P.R. China
A scheme for teleporting an unknown two-particle entangled state is proposed. In comparison with the recent protocol （Cola et al., Phys. Lett. A 337 （2005））, the entangled state as quantum channel required by this scheme is a single, partially entangled pair, which is much easier to prepare and maintain. Furthermore, a positive operator valued measure （POVM） is adopted and all kinds of transformations performed by sender and receiver are given in detail. It is shown that the probability of successful teleportation is twice the modulus square of the smaller Schmidt coefficient of the two-particle entangled state, and the fidelity can reach one.
An efficient two-step quantum key distribution （QKD） protocol with orthogonal product states in the （×）（n ≥3） Hilbert space is presented. In this protocol, the particles in the orthogonal product states form two particle sequences. The sender, Alice, first sends one sequence to the receiver, Bob. After Bob receives the first particle sequence, Alice and Bob check eavesdropping by measuring a fraction of particles randomly chosen. After ensuring the security of the quantum channel, Alice sends the other particle sequence to Bob. By making an orthogonal measurement on the two particle sequences, Bob can obtain the information of the orthogonal product states sent by Alice. This protocol has many distinct features such as great capacity, high efficiency in that it uses all orthogonal product states in distributing the key except those chosen for checking eavesdroppers.
