User-independent optical path length compensation scheme with sub-nanosecond timing resolution for a 1 × N quantum key distribution network system

Abstract

Quantum key distribution (QKD) networks constitute promising solutions for secure communication. Beyond conventional point-to-point QKD, we developed 1 × N QKD network systems with a sub-nanosecond resolution optical path length compensation scheme. With a practical plug-and-play QKD architecture and compact timing control modules based on a field-programmable gate array, we achieved long-term stable operation of a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>64</mml:mn> </mml:mrow> </mml:math> QKD network system. Using this architecture, 64 users can simultaneously share secret keys with one server, without using complex software algorithms and expensive hardware. We demonstrated the workings of a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>×</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:math> QKD network system using the fiber network of a metropolitan area.