Efficient entanglement purification in quantum repeaters

We present an efficient entanglement purification protocol (EPP) with controlled-not (CNOT) gates and linear optics. With the CNOT gates, our EPP can reach a higher fidelity than the conventional one. Moreover, it does not require the fidelity of the initial mixed state to satisfy F>1/2. If the initial state is not entangled, it still can be purified. With the linear optics, this protocol can get pure maximally entangled pairs with some probabilities. Meanwhile, it can be used to purify the entanglement between the atomic ensembles in distant locations. This protocol may be useful in long-distance quantum communication.     

一类稀疏约束下不适定反问题的求解

矩阵填充是一类稀疏先验下的不适定的反问题.首先阐述了矩阵填充的基本原理,指出只有当待求的矩阵满足不相关特性或秩-受限等距特性时,才有可能精确重构未知矩阵.Jain P等将矩阵的不相关特性与秩-受限等距特性联系起来,提出了仿射-受限等距特性,但没有说明秩-受限等距常数与不相关常数的关系,定理3给出了两者之间的的数值关系,有效的促进了矩阵填充的研究.接下来分析了矩阵填充中常用的几种算法,并在随后的仿真实验中对这几种算法的重构性能做了详细比较.     

Efficient entanglement purification in quantum repeaters

We present an efficient entanglement purification protocol(EPP) with controlled-not(CNOT) gates and linear optics.With the CNOT gates,our EPP can reach a higher fidelity than the conventional one.Moreover,it does not require the fidelity of the initial mixed state to satisfy F > 1/2.If the initial state is not entangled,it still can be purified.With the linear optics,this protocol can get pure maximally entangled pairs with some probabilities.Meanwhile,it can be used to purify the entanglement between the atomic ensembles in distant locations.This protocol may be useful in long-distance quantum communication.