Quantum key distribution over 40 dB channel loss using superconducting single photon detectors

TL;DR

This paper demonstrates a quantum key distribution system capable of secure communication over 42 dB channel loss and 200 km of optical fiber, utilizing superconducting single photon detectors to achieve record distances and key rates.

Contribution

First successful QKD experiment over 42 dB loss and 200 km fiber using superconducting detectors with high clock frequency and low noise.

Findings

Secure keys distributed over 42 dB loss and 200 km fiber

Achieved 17 kbit/s key rate over 105 km

Longest terrestrial QKD demonstrated to date

Abstract

Quantum key distribution (QKD) offers an unconditionally secure means of communication based on the laws of quantum mechanics. Currently, a major challenge is to achieve a QKD system with a 40 dB channel loss, which is required if we are to realize global scale QKD networks using communication satellites. Here we report the first QKD experiment in which secure keys were distributed over 42 dB channel loss and 200 km of optical fibre. We employed the differential phase shift quantum key distribution (DPS-QKD) protocol implemented with a 10-GHz clock frequency, and superconducting single photon detectors (SSPD) based on NbN nanowire. The SSPD offers a very low dark count rate (a few Hz) and small timing jitter (60 ps full width at half maximum). These characteristics allowed us to construct a 10-GHz clock QKD system and thus distribute secure keys over channel loss of 42 dB. In addition, we achieved a 17 kbit/s secure key rate over 105 km of optical fibre, which is two orders of magnitude higher than the previous record, and a 12.1 bit/s secure key rate over 200 km of optical fibre, which is the longest terrestrial QKD yet demonstrated. The keys generated in our experiment are secure against both general collective attacks on individual photons and a specific collective attack on multi-photons, known as a sequential unambiguous state discrimination (USD) attack.