纠缠的纯化和提取

纠缠的纯化和提取在量子信息的理论和实验上都是一个重要的方向，简单回顾了这个方向上的一些主要进展，并重点介绍了有限个拷贝情况下的纠缠提取。提出了准分离态和提取子空间的概念，得到了从一个混合态的有限个拷贝中提取纯纠缠态的必要条件及充要条件；并得到了有限个拷贝情况下的最有效的提取方案；考虑了这些结论在无限个拷贝的情况下的推广。

The Purification and Distillation of Entanglement

Distillation and purification of entanglement is an important field of quantum information both in theory and in experiment. This paper presents some main conclusions in this field, and discusses mainly the distillation of entanglement from finite copies of a mixed state. By using the conceptions of quasiseparable state and distillable subspace, we show a necessary condition and a sufficient and necessary condition of the distillability from finite copies of a mixed state. We also get the most efficient protocols of entanglement distillation for the case of finite copies. Finally we consider the generalization of these results to the case of infinite copies of a mixed state.