Study On Remote State Preparation In Noisy Environments Or Via Cavity Quantum Electrodynamics

Quantum information is a new subject combining quantum mechanics and classical information theory. It mainly includes quantum communication, quantum computation, and quantum simulation, etc. Quantum teleportation and remote state preparation are two typical protocols for transmitting quantum states in quantum communication field. In this thesis, we first investigate the influence of various Pauli noises on the remote preparation of two-and three-qubit states, and then present two schemes for the remote preparation of atomic states trapped in low-Q cavities using the technique of photonic Faraday rotation.It is well known that quantum entanglement plays an important role in the process of remote state preparation (RSP). Due to the inevitable interaction of quantum systems with their surrounding environments, it is very necessary and interested to take into account the effects of quantum noises on quantum communication process. First of all, we study the remote preparation of arbitrary two-and three-qubit states in various Pauli noisy environments. By analytically solving the master equation in the Lindblad form, the time evolution of the quantum channel consisting of EPR states is obtained. Then we calculate the fidelity and the corresponding average fidelity during the process of RSP. It is found that the fidelity and the corresponding average fidelity are different for the cases of different Pauli noises. Moreover, the influence of the quantum channel subject to noises acting in x directions on the RSP is the strongest while that subject to noise acting in z directions on the RSP is the weakest.At present, cavity quantum electrodynamics (QED) has become one of the most possible candidates to demonstrate quantum properties of atoms and light field. According to the input-output process of single-photon pulses regarding optical cavities, a certain angle rotation of the photonic polarization is possible to produce if there are large cavity decay and moderate coupling between cavity and atom. Inspired by this idea, we propose two schemes for remotely preparing the state of atoms confined in low-Q cavities via a photonic Faraday rotation, in which photon acts as the flying qubit between different cavities and strongly interacts with the atoms trapped inside the cavity. Thus our scheme is insensitive to both cavity decay and atomic spontaneous emission. For the sender Alice has complete knowledge of the original state to be remotely prepared, she can set the parameters of her own particles in whatever she wants and combine with single-qubit operation and Bell-state measurement, as a result, remote preparation of a single-atom state and a two-atom entangled state can be achieved successfully. Furthermore, the success probability of our RSP schemes can reach100%for the case that the original state is in real Hilbert space, and our schemes relax the experimental possibility compared with the corresponding quantum teleportation to some extent.