Concepedia

Faraday–Michelson system for quantum cryptography

Xiaofan Mo, Bing Zhu, Zheng‐Fu Han, You-Zhen Gui, Guang‐Can Guo

Optics Letters · 2005 · 194 citations · 15 references

Open access

TL;DR

Quantum key distribution offers unconditional security, yet existing experimental schemes fail for long‑distance fiber due to phase drift and Rayleigh backscattering. The authors aim to introduce a unidirectional, intrinsically stable quantum key distribution scheme using Michelson‑Faraday interferometers with 90° Faraday mirrors. The scheme employs Michelson‑Faraday interferometers where ordinary mirrors are substituted by 90° Faraday mirrors to achieve intrinsic stability. The demonstration achieved stable interference visibility over 175 km and enabled a 125 km key exchange with a QBER below 6 %, the longest field‑conditioned QKD experiment reported.

Abstract

Quantum key distribution provides unconditional security for communication. Unfortunately, current experimental schemes are not suitable for long-distance fiber transmission because of phase drift or Rayleigh backscattering. In this Letter we present a unidirectional intrinsically stable scheme that is based on Michelson-Faraday interferometers, in which ordinary mirrors are replaced with 90 degree Faraday mirrors. With the scheme, a demonstration setup was built and excellent stability of interference fringe visibility was achieved over a fiber length of 175 km. Through a 125 km long commercial communication fiber cable between Beijing and Tianjin, the key exchange was performed with a quantum bit-error rate of less than 6%, which is to our knowledge the longest reported quantum key distribution experiment under field conditions.