Implementing Quantum Communication Via Cavity QED

Quantum information is an interesting new subject, which is a combination of quantum mechanics and information science. Recently, quantum information has made a surprise progress both in theoretical and experimental fields. It has created many miracles which are unimaginable in classical information theory, such as absolute secure quantum key, quantum dense coding, quantum teleportation, and so on. And quantum communication is an important research field of quantum information, including quantum cryptography, quantum teleportation and quantum dense coding, etc. In this paper, the major is to present physical implementation of some quantum communication.Cavity quantum electrodynamics (CQED) is one of the key physical systems to implement quantum computer and quantum communication network. The idea is to trap several atoms in a small high finesse optical cavity. Quantum information can be stored in the internal states of atoms. All the trapped atoms in cavity are coupled to the field, resulting in interaction among atoms. In this paper, we discuss some applications of cavity QED with the main work as follows:(1) Implementing quantum secret sharing. In order to cut down the requirement on the quality factor of the cavity, the transition frequency between states is highly detuned from the cavity frequency and the cavity is only virtually excited. In the large detuning case, no energy exchange between the atoms and the cavity will happen, so the leakage of cavity is effectively suppressed.(2) Implementing quantum entanglement purification. In the scheme, atoms are trapped in one-side leaky cavities, and the systems evolve only in the space of dark state through adiabatic passage. There is no population in excited states, which is robust against to the atomic spontaneous emission. We implement entanglement purification based on the interference effect of the photons leaking out of the cavities and prepare the maximal entanglement of two distant atoms, which is significant toquantum communication.(3) Implementing the entanglement teleportation. In this scheme, we use the GHZ state as quantum channel, and the system of atom and cavity evolves adiabatically. Finally, through the detection of the leaky photons, the teleportation of entanglement state is realized.