A simple scheme is proposed to generate the W state of N A-type neutral atoms trapped in an optical cavity via Raman transition. Conditional on no photon leakage from the cavity, the N-qubit W state can be prepared perfectly by turning on a classical coupling field for an appropriate time. Compared with the previous ones, our scheme requires neither individual laser addressing of the atoms, nor demand for controlling N atoms to go through an optical cavity simultaneously with a constant velocity. We investigate the influence of cavity decay using the quantum jump approach and show that the preparation time decreases and the success probability increases with atom number because of a collective enhancement of the coupling.
The loss of a quantum channel leads to an irretrievable particle loss as well as information. In this paper, the loss of quantum channel is analysed and a method is put forward to recover the particle and information loss effectively using universal quantum error correction. Then a secure direct communication scheme is proposed, such that in a loss channel the information that an eavesdropper can obtain would be limited to arbitrarily small when the code is properly chosen and the correction operation is properly arranged.
