Shou Zhang

Secure direct communication based on secret transmitting order of particles

We propose the schemes of quantum secure direct communication based on a secret transmitting order of particles. In these protocols, the secret transmitting order of particles ensures the security of communication, and no secret messages are leaked even if the communication is interrupted for security. This strategy of security for communication is also generalized to a quantum dialogue. It not only ensures the unconditional security but also improves the efficiency of communication.

Fast CNOT gate via quantum Zeno dynamics

Based on the quantum Zeno dynamics, we propose two approaches for directly implementing a CNOT gate in a cavity QED system instead of constructing it from elementary gates. The first approach works in the decoherence-free subspaces (DFS) due to the quantum Zeno effect, which is robust against cavity decay. Based on the first model, we then propose the second approach which takes advantage of stimulated Raman adiabatic passage (STIRAP) with only six pulses; thus it is insensitive to the atomic spontaneous emission. The two schemes are suitable for different decoherence parameters. The strictly numerical simulation shows that the average gate fidelities for the two methods are relatively high.

Schemes for the generation of multipartite entanglement of remote atoms trapped in separate optical cavities

Based on the interference effect of polarized photons leaking out of separate cavities, we propose schemes for the generation of the N-atom Greenberger–Horne–Zeilinger (GHZ) state, three-atom W state and a genuine four-atom entangled state |χ. In these schemes, each of the atoms is trapped separately in a remote optical cavity, and the possible spontaneous channels induced by the excited atoms lead to the coherent superposition of the states of the atoms. The desired multipartite entangled states can be generated with a certain success probability by the subsequent detection of the polarized photons in different modes. The schemes would be useful steps towards long-distance quantum communication, distributed quantum computation and constructing remote quantum information processing networks.

Swap gate and controlled swap gate based on a single resonant interaction with cavity quantum electrodynamics

A scheme for implementing a swap gate is proposed with atoms sent through a microwave cavity. This scheme can be directly generalized to realize the controlled swap gate through appropriate changes of the coupling constants between the atoms and cavity. Moreover, an N-qubit controlled swap gate can be achieved without changing the gating time as the number of qubits increases.

Simple schemes for generating the three-atom W state and the Greenberger?Horne?Zeilinger state among nonidentical atoms

We present two schemes for generating the three-atom W state and the GHZ state with one ?-type atom and two 2-level atoms interacting resonantly with two modes or one mode of a two-mode field in turns. The schemes neither require the three atoms to go through the cavity simultaneously (which is difficult to realize in experiment), nor require the detection of photons. The schemes work beyond the strong-coupling regime, so that we can obtain high-fidelity entanglement.