Over the course of the last five decades, there has been substantial growth in conventional network routing design, transitioning from small static node networks to vast systems connecting billions of devices. This evolution has been facilitated by the separation of concerns principle, which involves integrating network functionalities into graph or random network designs and utilizing specific protocols to enable diverse communication capabilities. The landscape of quantum networks is rapidly evolving, presenting new paradigms in information transmission and processing. Routing protocols play a pivotal role in establishing efficient communication pathways within quantum networks, enabling the transmission of quantum states and entanglement across interconnected nodes. The objective of this paper is to shed light on existing entanglement routing design techniques within quantum networks. The design of quantum entanglement routing necessitates a departure from conventional network protocols due to its unique considerations of quantum entanglement and entanglement swapping. However, the implementation of these techniques is fraught with significant challenges, including quantum system decoherence and noise, limitations on communication ranges, and the need for specialized hardware. The paper initiates by surveying critical research in quantum routing design techniques, then delves into essential aspects of the routing concept, associated quantum operations, and the step-wise process for establishing efficient and resilient quantum networks. In summary, this paper provides an overview of the current landscape of quantum entanglement routing techniques. It outlines their core principles, protocols, and challenges, while also highlighting potential applications and charting future directions for research and development.

Quantum networks hold the potential to revolutionize a variety of fields by surpassing the capabilities of their classical counterparts. Many of these applications necessitate the sharing of high-fidelity entangled pairs among communicating parties. However, the inherent nature of entanglement leads to an exponential decrease in fidelity as the distance between quantum nodes increases. This phenomenon makes it challenging to generate high-fidelity entangled pairs and preserve information in quantum networks. To tackle this problem, we utilized two strategies to ensure high-fidelity entangled pairs and information preservation within a quantum network. First, we use closeness centrality as a metric to identify the closest nodes in the network. Second, we introduced the trace-distance based path purification (TDPP) algorithm, specifically designed to enable information preservation and path purification entanglement routing. This algorithm identifies the shortest path within quantum networks using closeness centrality and integrates trace-distance computations for distinguishing quantum states and maintaining end-toend (E2E) entanglement fidelity. Simulation results demonstrate that the proposed algorithm improves network throughput and E2E fidelity while preserving information compared to existing methods.

The use of quantum cryptography in everyday applications has gained attention in both industrial and academic fields. Due to advancements in quantum electronics, practical quantum devices are already available in the market, and ready for wider use. Quantum Key Distribution (QKD) is a crucial aspect of quantum cryptography, which involves generating and distributing symmetric cryptographic keys between geographically separated users using principles of quantum physics. Many successful QKD networks have been established to test different solutions. The objective of this paper is to delve into the potential of utilizing established routing design techniques in the context of quantum key distribution, a field distinguished by its unique properties rooted in the principles of quantum mechanics. However, the implementation of these techniques poses substantial challenges, including quantum memory decoherence, key rate generation, latency delays, inherent noise in quantum systems, limited communication ranges, and the necessity for highly specialized hardware. This paper conducts an in-depth examination of essential research pertaining to the design methodologies for quantum key distribution. It also explores the fundamental aspects of quantum routing and the associated properties inherent to quantum QKD. This paper elucidates the necessary steps for constructing efficient and resilient QKD networks. In summarizing the techniques relevant to QKD networking and routing, including their underlying principles, protocols, and challenges, this paper sheds light on potential applications and delineates future research directions in this burgeoning field.