Yan Pei-Shun, Zhou Lan, Zhong Wei, Sheng Yu-Bo
Opt Express. 2021 Jan 18;29(2):571-583. doi: 10.1364/OE.409931.
High quality time-bin entanglement is widely exploited to achieve the purposes of fundamental tests of physics and the implementation of quantum communication protocols both in free space and optical fiber propagation. However, the imperfect approaches of generating time-bin entangled state will degrade its quality and limit its practical application. Entanglement purification is to distill high quality entangled states from low quality entangled states. In this paper, we present the first entanglement purification protocol (EPP) for time-bin entanglement. We first explain this EPP for two-photon time-bin entangled state and then extend it to the system of multi-photon time-bin entangled state. We also design a possible realization of this EPP with practical spontaneous parametric down conversion (SPDC) source. Differ from the conventional EPPs, this EPP does not require the sophisticated controlled-not (CNOT) gate or similar operations, and it uses the feasible sum-frequency generation (SFG) to perform the purification. Moreover, the double-pair noise emitted from the SPDC source can be eliminated automatically which is the other advantage of this EPP. If we combine with the faithful entanglement swapping, this EPP may have potential to be a part of full quantum repeaters.
高质量的时间-bin纠缠被广泛用于实现物理基本测试以及在自由空间和光纤传播中实施量子通信协议的目的。然而，生成时间-bin纠缠态的不完善方法会降低其质量并限制其实际应用。纠缠纯化是从低质量纠缠态中提炼出高质量纠缠态。在本文中，我们提出了首个用于时间-bin纠缠的纠缠纯化协议（EPP）。我们首先针对双光子时间-bin纠缠态解释此EPP，然后将其扩展到多光子时间-bin纠缠态系统。我们还设计了一种利用实际的自发参量下转换（SPDC）源实现此EPP的可能方案。与传统的EPP不同，此EPP不需要复杂的受控非（CNOT）门或类似操作，并且它使用可行的和频产生（SFG）来执行纯化。此外，SPDC源发射的双对噪声可以自动消除，这是此EPP的另一个优点。如果我们将其与可靠的纠缠交换相结合，此EPP可能有潜力成为全量子中继器的一部分。
