Joint Noise Quantum Communication And Quantum Gates Studies

Quantum communication is one of the most important branches of quantum information, which is the combination of quantum mechanics and information theory. With the application of quantum mechanics, several difficulties in classical information field have been solved. Physical principle have been exploited to guarantee the absolute security of information transmission. This novel accomplishment of communication has great power for the development of information field. Many physicists and IT experts concentrate on this area which develops rapidly in recent thirty years.Noise should be considered in quantum communication for the interactions between quantum system and environment. In this thesis, several communication schemes of quantum key distribution (QKD) and quantum secret sharing (QSS) were proposed over different collective noise channels. We also built a noise-tolerant logical qubits CNOT gate with weak cross-Kerr nonlinearity. In addition, we built a two-split allowable generalized quantum gate and a quantum key distribution in weak-coupling cavity QED regime.Under the collective-rotation noise and collective-dephasing noise, QKD and QSS schemes based on the decoherence-free subspaces (DFSs) are proposed. Two physical qubits are used to construct a logical qubit to transmit one bit information. Single-photon measurements are easy to realize and used in these schemes, in which almost all photons are used as information qubits. The efficiency approaches to 100% theoretically.In the field of quantum gate constructing, we proposed a scheme of logical qubit quantum gates and an allowable generalized quantum gate using weak cross-Kerr nonlinearity material. As the noise exists everywhere, it is an important problem to establish corresponding logical qubit quantum gates. At first, we presented a scheme for 3-qubit parity check. Then we constructed logical qubit CNOT gates with DFSs. Each logical control qubit and target qubit contains 2 photons, which form DFSs of collective-rotating noise or collective-dephasing noise. Only one ancillary photon is needed in the scheme. The probability of success is nearly deterministic. We also give an efficient physical realization of a double-slit duality quantum gate. The success probability is 50%. Asymmetrical slits duality control gate can also be constructed conveniently. Both of the special quantum control gate could be realized easily by our current experimental technologies.Finally, we present a quantum key distribution scheme using weak-coupling cavity QED regime. Hybrid entanglement states of a photon and an electron are used to distribute the information. We just need to transmit photons without storage. The electron confined in quantum dot, which is embedded in microcavity, is held by one of legitimate users all the while. Only single photon polarization and electron of spin measurements are used in our protocol. Linear optical apparatus as special polarizing beam splitter and single photon operations makes it more convenient to realize by the current technology. This is a secure scheme. The efficiency will approach 100%.