Multi-Photon Entanglement Purification Based On The LOW-Q Cavity

In the1980s, with the development of quantum mechanics and information sci-ence, quantum information as a new interdiscipline has emerged. Quantum entan-glement is the core of quantum information processing (QIP), which is an important resource of quantum communication and quantum computing tasks. In the process of long distance quantum communication, entangled system is affected by external environment inevitably, which leads to the degradation of entanglement and affects the quality of quantum communication. However, resorting to the quantum entan-glement purification, we can extract the pure entangled state from the mixed state system which suffered the decoherence effect. Then, we can transfer the quantum information more safely and accurately. So the research of quantum entanglement purification has a great significance in quantum information science.It is well known that cavity quantum electrodynamics (QED) system is an ef-fective platform to understand the basic principle of quantum mechanics and realize QIP. But we find that most of QIP tasks based on QED require the optical cavity with high quality, and need the strong coupling limit between cavity and trapped atoms. However, it’s difficult to get high quality optical cavity in the current exper-imental condition. Therefore, much attention has been focused on how to use the low-Q cavity to realize QIP.Base on above reasons, we propose a multi-photon entanglement purification protocol using a low-Q optical cavity. In this dissertation, we first complete the entanglement purification of photonic Bell state by the low-Q optical cavity. Then we propose a entanglement purification protocol of photonic GHZ state. Finally, we generalize the entanglement purification protocol to multi-photon system and we achieve entanglement purification of multi-photon system. The process of our entanglement purification protocols can be divided into two parts:bit-flip error correction and phase-flip error correction. All kinds of errors that may occur in the photonic system can be corrected by the two processes. And we can get some high-fidelity entangled photonic states. The multi-photon entanglement purification protocol can be completed by only using three level atoms, low-Q cavities, and basic optical elements. The function of these elements can be realized in the current experimental technique of the cavity QED and quantum optics. And people have realized optical Faraday rotation effect in experiment, which makes our protocols more feasibility in current experiment.