The optical Bell State Analyzer (BSA) plays a key role in the optical generation of entanglement in quantum networks. The optical BSA is effective in controlling the timing of arriving photons to achieve interference. It is unclear whether timing synchronization is possible even in multi-hop and complex large-scale networks, and if so, how efficient it is. We investigate the scalability of BSA synchronization mechanisms over multiple hops for quantum networks both with and without memory in each node. We first focus on the exchange of entanglement between two network nodes via a BSA, especially effective methods of optical path coordination in achieving the simultaneous arrival of photons at the BSA. In optical memoryless quantum networks, including repeater graph state networks, we see that the quantum optical path coordination works well, though some possible timing coordination mechanisms have effects that cascade to adjacent links and beyond, some of which was not going to work well of timing coordination. We also discuss the effect of quantum memory, given that end-to-end extension of entangled states through multi-node entanglement exchange is essential for the practical application of quantum networks. Finally, cycles of all-optical links in the network topology are shown to may not be to synchronize, this property should be taken into account when considering synchronization in large networks.

翻译：光学贝尔态分析仪在量子网络的光学纠缠生成中起着关键作用。光学BSA通过有效控制到达光子的时序以实现干涉。尚不明确在多跳及复杂大规模网络中是否能够实现时序同步，若可行，其效率如何。我们研究了有/无节点存储的量子网络中多跳BSA同步机制的可扩展性。首先聚焦通过BSA在两个网络节点间交换纠缠的过程，重点探讨实现光子同时到达BSA的有效光路协调方法。在无存储光学量子网络（包括中继图态网络）中，我们发现量子光路协调效果良好，但部分可能的时序协调机制会对相邻链路及更远链路产生级联效应，其中某些机制在时序协调方面表现不佳。考虑到通过多节点纠缠交换实现纠缠态端到端扩展对量子网络实际应用至关重要，我们进一步讨论了量子存储的影响。最后论证了网络拓扑中的全光链路环路可能无法实现同步，在大型网络的同步设计中需考虑该特性。