| Quantum information uses quantum states as the main information carriers, and quantum information storage, processing and transmission are dependent on the basic principles of quantum mechanics. Compared with the classical information science, quantum information science has many advantages, such as parallel computation, absolute security, and large information capacity and so on. In particular, quantum entanglement plays a very important role in quantum information processing. Currently, the candidate hardware systems of quantum information processing are nuclear magnetic resonance (NMR), ion trap, cavity QED, etc. However, these quantum systems are easily affected by the environment which leads to decoherence, so the preparation of quantum state becomes not perfect, and thus it is difficult to realize remote quantum information processing. In recent years, due to the easy manipulation and the long coherent time, quantum dots cavity QED system attracts more and more attention, and is widely applied to the quantum information processing. Nowadays, photon has become a good flying qubit for quantum information processing, due to its quick speed and the advantage of easy manipulation in experiment. Now, the photons and quantum dots cavity QED system provide a good platform for us to realize the remote processing of quantum information. The interaction between photons and quantum dots spin embedded in cavity can produce entanglement between the photon and the spin. Taking advantage of this phenomenon, it is possible for us to implement the quantum information processing and transmission for quantum dots with the help of photons and quantum dots plus cavity system. Because of the short decoherence time, photon is not the best choice for information storage. So, in order to effectively store and protect entanglement, we need to prepare entanglement among quantum dots electronic spins.In this master thesis, we make use of quantum dots plus cavity system to prepare entanglement state between the electronic spins of quantum dots and concentrate the unknown nonmaximally entangled. Based on quantum-dots plus double-sided cavity (double-sided cavity has two partially reflecting mirrors) system and photons, the following two works have been done in this thesis:1. Scheme for realizing remote preparation and transfer of quantum state. The results show that this scheme works fine both in ideal and actual conditions. In addition, remote preparation of entangled channel and the transfer of quantum state are realized simultaneously in one process, which greatly reduce the complexity of the scheme.2. Scheme for implementing entanglement concentration for unknown nonmaximally entangled states based on the entanglement swapping. The maximally entangled state can be generated between electron spins without the direct interaction between them. The advantages of this scheme are as follows. Firstly, the scheme can generate both bipartite and quadripartite maximally entangled states. Secondly, even when there exists a slight difference between the two initial unknown nonmaximally entangled states, the output state is still very close to the ideal maximally entangled state. In addition, only photons are detected during the process, which makes the scheme simple and feasible. |
