Provably-Secure and High-Rate Quantum Key Distribution with Time-Bin Qudits

摘要

The security of conventional cryptography systems is threatened in theforthcoming era of quantum computers. Quantum key distribution (QKD) featuresfundamentally proven security and offers a promising option for quantum-proofcryptography solution. Although prototype QKD systems over optical fiber havebeen demonstrated over the years, the key generation rates remain severalorders-of-magnitude lower than current classical communication systems. In aneffort towards a commercially viable QKD system with improved key generationrates, we developed a discrete-variable QKD system based on time-bin quantumphotonic states that is capable of generating provably-secure cryptographickeys at megabit-per-second (Mbps) rates over metropolitan distances. We usehigh-dimensional quantum states that transmit more than one secret bit perreceived photon, alleviating detector saturation effects in the superconductingnanowire single-photon detectors (SNSPDs) employed in our system that featurevery high detection efficiency (of over 70%) and low timing jitter (of lessthan 40 ps). Our system is constructed using commercial off-the-shelfcomponents, and the adopted protocol can readily be extended to free-spacequantum channels. The security analysis adopted to distill the keys ensuresthat the demonstrated protocol is robust against coherent attacks, finite-sizeeffects, and a broad class of experimental imperfections identified in oursystem.