# First Request First Service Entanglement Routing Scheme for Quantum Networks
## 6 Conclusions  
Quantum networks enable many applications beyond the reach of classical networks, including distributed quantum computing, remote quantum clock synchronization, and distributed quantum sensing, and are already stepped into the entanglement distribution network stage. An active wavelength multiplexing entanglement routing scheme is desiderated to satisfy the dynamic connection demands of paired users in large-scale quantum networks. In this article, we first model the entanglement distribution network into a directed graph, where the nodes represent the entangled photon source, the wavelength routing devices, and the users, and the edges stand for the quantum links (fibers or free-space links) among nodes. Different to classically modeled nodes, the pass-through loss matrix among all ports within a node is described for each supported wavelength channel. Afterwards, we propose a novel first request first service (FRFS) entanglement routing scheme for quantum networks, which performs the modified Dijkstra algorithm to find the path with the lowest loss from the entangled photon source to each paired user in order. The evaluation results show that the proposed FRFS entanglement routing scheme can be applied to large-scale and dynamic topology quantum networks.  
As the quantum entanglement distribution network scales up, configuring the wavelength routing network with various topologies manually is difficult for the network administrator. Using our FRFS routing scheme, the management difficulty can be significantly reduced. With the proposed weighted graph quantum network model and the modified lowest loss path searching Dijkstra algorithm, our work opens up the quality of service (QoS) entanglement routing problems for quantum networks. Various entanglement routing strategies, such as fidelity first and bandwidth first, can be further studied to provide QoS guarantees for users. Furthermore, the proposed FRFS entanglement routing scheme can be performed in quantum memory-assisted networks by replacing the QoS metric with the entanglement swapping success rate.  
Conceptualization, B.L. ([PERSON] 2); formal analysis, S.-C.L. and B.-Y.T.; methodology, S.-C.L., B.-Y.T. and B.L. ([PERSON] 2); validation, S.-C.L. and B.-Y.T.; evaluate experiments, S.-C.L., B.-Y.T., B.L. ([PERSON] 2), H.Z. and H.-C.Y.; writing--original draft, S.-C.L. and B.-Y.T.; writing--review and editing, B.L. ([PERSON] 2), W.-R.Y. and B.-Y.T.; funding acquisition, W.-R.Y. and B.L. ([PERSON] 1) All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China under Grant No.61972410, the Research Plan of National University of Defense Technology under Grant No. ZK19-13 and No.19-QNCJ-107.  
Not applicable.  
The datasets and code analyzed during the current study are available from the corresponding authors on reasonable request.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
FRFS First request first service DWDM Dense wavelength division multiplexer WSS Wavelength selective switches BS Beam splitter OS Optical switch AOS All-pass optical switch TDM Time division multiplexing WDM Wavelength division multiplexing ITU International Telecommunication Union