Micro-Ring Resonators as Quantum State Analyzers for DPS-QKD in the Shortwave and Telecom Bands

Currently employed asymmetric cryptosystems for securing communications are greatly threatened by the advent of quantum-computational power. While the migration to quantum-safe alternatives employing quantum key distribution (QKD) is already ongoing, the currently available systems still face major deployment challenges due to their high complexity, cost and size. To this end, we investigate shortwave differential phase-shift (DPS) QKD benefitting from highly efficient silicon detectors and compare its performance to traditional near-infrared DPS-QKD implementations, where both layouts employ a micro-ring resonator as a compact quantum state analyzer. We demonstrate secure-key generation for QKD links furnished by standard telecom single-mode fiber with a reach of up to 330 m in the shortwave band, and up to 24 km in the near-infrared. In an additional step, we also investigate alternative transmitter implementations to reduce complexity at both link ends. Towards this direction, we employ a single-mode vertical cavity surface emitting laser or a directly modulated laser for the purpose of direct phase encoding and assess suitable application scenarios at both QKD wavelength domains.