An improved quantum secure direct communication （QSDC） protocol is proposed in this paper. Blocks of entangled photon pairs are transmitted in two steps in which secret messages are transmitted directly. The single logical qubits and unitary operations under decoherence free subspaces are presented and the generalized Bell states are constructed which are immune to the collective noise. Two steps of qubit transmission are used in this protocol to guarantee the security of communication. The security of the protocol against various attacks are discussed.
The ground-state entanglement in a transverse spin-1/2 XX chain with a magnetization current is studied. By introducing a magnetization current to the system, a quantum phase transition to current-carrying phase may be presented with the variation of the driving field λ for the magnetic field h 〉 1; and the ground-state entanglement arises simultaneously at the critical point of quantum phase transition. In our model, the introduction of magnetization current may result in more entanglement between any two nearest-neighbour spins.
Weak cross-Kerr media provides additional degrees of freedom of qubits in quantum information processing.In this paper,by exploiting weak cross-Kerr nonlinearity,we propose an optical implementation scheme of one-dimensional quantum random walks. The random walks are described by the interaction of single photons with cross-Kerr media.The proposed scheme can also be used to implement one-dimensional quantum random walks on an infinite line.
This paper has proposed a generalized quantum state sharing protocol of an arbitrary two-particle state using non-maximally GHZ states and generalized Bell state measurement.The sender Alice performs two-particle generalized Bell state measurements on her two particles in the state sharing process and the controller takes measurements on his particles and transfers the quantum information to the receiver with entanglement swapping by the cooperation of the other agents.It is found that the use of nonmaximally entangled state in quantum state sharing has enabled the secure sharing of the quantum state.
WANG Chuan 1,2,ZHANG Yong 1,2 & JIN GuangSheng 1,2 1 School of Science,Beijing University of Posts and Telecommunications,Beijing 100876,China
