REDiP: Ranked Entanglement Distribution Protocol for the Quantum Internet

The distribution of entangled qubit pairs to end nodes is the key requirement of a quantum network to enable qubit state transmission through quantum teleportation. Existing protocols for entanglement distribution fix a specific swapping order on the involved quantum repeaters and delegate entanglement purification to upper-layer protocols. This limitation is problematic because entangled states tend to degrade due to quantum noise, and they cannot be purified if their fidelity (i.e., quality) falls below a certain threshold. It is therefore of the utmost importance to co-plan entanglement swapping and purification to achieve a target end-to-end fidelity. In this work, we present the Ranked Entanglement Distribution Protocol (REDiP), which overcomes the aforementioned limits by including the "ranks" mechanism to configure the ordering of both purification and entanglement swapping steps. We show how REDiP can easily be configured to implement custom entanglement swapping and purification strategies, including (but not restricted to) those adopted in two recent works. We also propose an algorithm to estimate the bandwidth to allocate on every link of the REDiP path, and we provide a set of guidelines on how REDiP ranks can be configured depending on user requirements and hardware configuration. Such guidelines are driven by original insights into purification performance. We conduct simulations to verify our results and assess the impact of different REDiP configurations on the performance of a repeater network, in terms of throughput and fidelity.