Strategies for Implementing a Single-detector Polarization-encoded Quantum Key Distribution Receiver
Cameron Simmons, Ross J. Donaldson · 2024
Discrete-variable quantum key distribution (QKD) requires the use of highly sensitive single-photon detectors (SPD) to detect decoded quantum states. These can form a significant portion of the cost and the physical layer vulnerabilities in a QKD system. Previously, a single-detector architecture which reduced the cost of simple, polarization-encoded fiber QKD systems was proposed, which decoded polarization states into varying fiber delays before reaching a single SPD. We describe the parameter space available for a single detector receiver and, using simulation, optimise performance for a given example. It is demonstrated that the order of state delays can be changed to reduce quantum bit error rate (QBER), and that delay change between states need only exceed some small minimum value in the ns range, which saves on fiber length, weight and cost, as well as loss. We also explore time gating and efficient (asymmetric basis selection) BB84 to reduce QBER. This work improves the understanding and performance of single-SPD-based QKD receivers, allowing simpler and more robust receivers with fewer physical loopholes and a lower cost, reducing the barrier to entry of fiber QKD.