Generation And Application Of Quantum Entangled States

The quantum information, a new interdisciplinary in last decade, has a very wide range of applications in the field of quantum physics, such as quantum telepor-tation, quantum dense coding, quantum computing and so on. Because of its wide application prospects and scientific significance, many researchers have paid a great attention to it and have achieved many important results. In quantum information processing, storing, denoting and extracting of information are dependent on quan-tum states and their evolution. Because quantum entanglement is associated with the peculiar nonclassical correlations, it plays an important role in quantum infor-mation processing and is at the heart of quantum information, so the main task of quantum information science is to investigate and prepare quantum entangled states.In this paper, we prepare a x-type entangled state|χ00>3214 by using linear op-tical elements, conventional photon detector and input-output of the cavity. This entangled state violates optimally a new Bell inequaliaty and is robust against lo-cal operations. Moreover, it has been shown that the degree of entanglement with von Neumann measure between atoms (1,2) and atoms (3,4) is higher than of the |χ00>3214-like state generated in ion-trap scheme [Phys. Rev. A,2008,78(2):024301]. The linear optical elements and conventional optical detector in our scheme are sim-ple and accessible in experiments, which makes the scheme more feasible with cur-rent technology. Due to the weak interaction between photons and the environment, choosing photons as information carriers can cut down the effects of environmental noise. And we can obtain the state|χ00>3214 if there is no photon loss.Quantum entanglement has been used widely in quantum information. We pro-pose schemes of quantum dense coding and quantum teleportation with quantum entangled states in cavity QED, respectively. In the scheme of quantum dense cod-ing, we use non-maximally entangled state as quantum channel, and let two identical two-level atoms driven by a classical field interacting with a single-mode cavity field. Choosing the interaction time (?) and Rabi frequencyΩappropriately, we can realize dense coding with a certain probability by making some unitary transformations and single-particle measurements. In the scheme of teleporting a three-atom entangled W state in cavity QED, three EPR pairs are chosen as quantum channel shared by the sender and the receiver. By atom-cavity-field interaction and appropriate unitary transformations, the three-atom entangled W state can be teleported suc-cessfully.