Multi-photon QKD for Practical Quantum Networks

TL;DR

This work investigates practical quantum networks under multiphoton QKD by comparing Decoy-state, Three-Stage, and E91 protocols across line, grid, ring, and torus topologies. Using a Matlab-based simulator, it models attenuation, decoherence, and multi-photon bursts to quantify how topology interacts with protocol performance and to derive a sigmoid-like distance–burst relation that predicts stable transmission ranges. Key contributions include showing that the Three-Stage protocol can outperform others in several topologies, especially torus and grid, and deriving a mathematical framework linking burst size to maximum stable distance. The findings provide actionable guidance for designing scalable quantum networks and point to future work on generalizing the burst-distance relationship across topologies and integrating quantum-augmented network concepts.

Abstract

Quantum key distribution (QKD) will most likely be an integral part of any practical quantum network in the future. However, not all QKD protocols can be used in today's networks because of the lack of single-photon emitters and noisy intermediate quantum hardware. Attenuated-photon transmission, typically used to simulate single-photon emitters, severely limits the achievable transmission distances and makes the integration of the QKD into existing classical networks, that use tens of thousands of photons per bit of transmission, difficult. Furthermore, it has been found that protocol performance varies with topology. In order to remove the reliance of QKD on single-photon emitters and increase transmission distances, it is worthwhile to explore QKD protocols that do not rely on single-photon transmissions for security, such as the 3-stage QKD protocol, which can tolerate multiple photons in each burst without information leakage. This paper compares and contrasts the 3-stage QKD protocol with conventional QKD protocols and its efficiency in different network topologies and conditions. Furthermore, we establish a mathematical relationship between achievable key rates to increase transmission distances in various topologies.

Figures (13)

• Figure 1: Schematic diagram representing the working of the three-stage protocol.
• Figure 2: Different topologies used in our QKD simulations (all of the topology profiles are generated through our simulations directly).
• Figure 3: Working of the quantum repeater: Starts with two sets of entangled bell-pair between Alice-QR and QR-Bob. Then, we perform an entanglement swap between the nodes to create a final entangled Bell state pair between Alice and Bob. The curly line represents an entangled pair.
• Figure 4: Schematic representation of the Torus topology. Red lines highlights the connection logic between user nodes.
• Figure 5: Comparison of Performance of different QKD Protocols over Direct Topology.