Generation Of Multipartite Entangled State

One of the most fundamental concepts in the quantum physics is that of entanglement. Entanglement has been found to be important not only for pro-viding a useful tool to disprove local hidden variable theories, but also for its potential applications in many quantum information processes, such as quan-tum teleportation, quantum cryptography, quantum computers, etc. Therefore, it is of key importance to find reliable strategies for their implementation. Over last decades, much effort have been devoted to the generation and engineering entangled states. Beyond the applications to conventional quantum computa-tion, entangled states of more than two quantum systems have been used as crucial resources for new directions in quantum information processing such as measurement-based quantum computation, quantum secret sharing, and quan-tum simulation. In addition, entangled state with spatially separated subsystems provides a very useful tool for the investigation of distributed quantum compu-tation. As a result, increasing attention is attracted to the manipulation and creation of multipartite entangled states with spatially separated physical sys-tems.In the thesis, some simple theoretical schemes are proposed for preparing multipartite entangled states with distant quantum systems. The main content of the dissertation is shown as follows:Based on the selective photon emission and absorption, a simple scheme is proposed to realize an N-qubit Greenberger-Home-Zeilinger (GHZ) state with distant atoms trapped in spatially separated bimodal cavities coupled by optical fibres. The excited levels of the A-type atoms are eliminated adiabati-cally under a large detunning condition. Only one step is required for realization of an N-qubit GHZ state and the calculation shows that the present scheme is ro-bust with respect to the deviation of experimental parameters and decoherence processes.Based on the fractional stimulated Raman adiabatic passage (f-STIRAP), two schemes are provided to implement N-qubit W states. One scheme is for the preparation of W state with remote atoms trapped in spatially separated cavities connected with optical fibres. Another scheme is to entangle spatially sepa-rated self-assembled semiconductor quantum dot molecules (QDMs). In the QDM, the electron tunneling between the two quantum dots can be controlled by placing a gate electrode. Both of schemes are tolerant to device parameter nonuniformity and do not need to accurately control the experimental time.The nitrogen-vacancy (N-V) center in diamond is considered to be a promising solid-state candidate for quantum information process. An alterna-tive scheme is proposed for the generation of an N-qubit GHZ state with distant N-V centers confined in spatially separated photonic crystal (PC) nanocavities via nanocavity input-output process. A scheme to generate three-dimensional entanglement with two nitrogen-vacancy (N-V) centres coupled strongly to whispering gallery modes in a silica microsphere is proposed also.In a word, we hope that our investigadon presented in this dissertation may be helpful not only in realizing experimentally multipartite entanglement, but also in promoting the development in quantum information science.