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

TL;DR

This paper presents a high-rate, secure quantum key distribution system using time-bin qudits that achieves megabit-per-second key rates over metropolitan distances, leveraging high-dimensional states and commercial components.

Contribution

The authors develop a practical, high-speed QKD system based on time-bin qudits with provable security, improving key rates significantly over previous implementations.

Findings

Achieved Mbps key generation rates over metropolitan distances.

Utilized high-dimensional quantum states to transmit multiple bits per photon.

System is secure against coherent attacks and robust to experimental imperfections.

Abstract

The security of conventional cryptography systems is threatened in the forthcoming era of quantum computers. Quantum key distribution (QKD) features fundamentally proven security and offers a promising option for quantum-proof cryptography solution. Although prototype QKD systems over optical fiber have been demonstrated over the years, the key generation rates remain several orders-of-magnitude lower than current classical communication systems. In an effort towards a commercially viable QKD system with improved key generation rates, we developed a discrete-variable QKD system based on time-bin quantum photonic states that is capable of generating provably-secure cryptographic keys at megabit-per-second (Mbps) rates over metropolitan distances. We use high-dimensional quantum states that transmit more than one secret bit per received photon, alleviating detector saturation effects in the superconducting nanowire single-photon detectors (SNSPDs) employed in our system that feature very high detection efficiency (of over 70%) and low timing jitter (of less than 40 ps). Our system is constructed using commercial off-the-shelf components, and the adopted protocol can readily be extended to free-space quantum channels. The security analysis adopted to distill the keys ensures that the demonstrated protocol is robust against coherent attacks, finite-size effects, and a broad class of experimental imperfections identified in our system.