标题： 撤销损失对量子纠缠的影响 显示英文标题

标题： Undoing the effect of loss on quantum entanglement

摘要： 纠缠蒸馏是一种通过概率性方式增强和纯化量子纠缠强度的过程。 它是许多量子通信和计算协议中的关键步骤。 特别是，纠缠蒸馏是量子中继器的必要组成部分，量子中继器是一种抵消由于通信线路损耗而导致的纠缠退化的设备。 在这里，我们报告了一项关于蒸馏光的爱因斯坦-波多尔斯基-罗森（EPR）态的实验，这是连续变量纠缠的主要工具，使用了无噪声放大技术。 与先前的实现不同，我们的技术所能够达到的纠缠增强因子没有根本限制，并且允许恢复具有宏观纠缠水平的EPR态，无论初始纠缠有多低或损耗有多高。 特别是，在其中一个EPR模式经过一个损耗因子为20的信道后，我们恢复了原始的纠缠水平。 我们蒸馏态中的纠缠程度高于通过类似损耗信道直接传输任何态所能达到的程度。 这是实现实际连续变量量子中继器以及其他CV量子协议的关键基准步骤。 显示英文摘要

摘要： Entanglement distillation is a process via which the strength and purity of quantum entanglement can be increased probabilistically. It is a key step in many quantum communication and computation protocols. In particular, entanglement distillation is a necessary component of the quantum repeater, a device which counters the degradation of entanglement that inevitably occurs due to losses in a communication line. Here we report an experiment on distilling the Einstein-Podolsky-Rosen (EPR) state of light, the workhorse of continuous-variable entanglement, using the technique of noiseless amplification. In contrast to previous implementations, the entanglement enhancement factor achievable by our technique is not fundamentally limited and permits recovering an EPR state with a macroscopic level of entanglement no matter how low the initial entanglement or how high the loss may be. In particular, we recover the original level of entanglement after one of the EPR modes has passed through a channel with a loss factor of 20. The level of entanglement in our distilled state is higher than that achievable by direct transmission of any state through a similar loss channel. This is a key bench-marking step towards the realization of a practical continuous-variable quantum repeater and other CV quantum protocols.