Practical gigahertz quantum key distribution robust against channel disturbance

Area of Science:

• Quantum communication
• Secure communication technologies
• Optics and photonics

Background:

• Quantum key distribution (QKD) offers a secure communication solution.
• Real-world QKD deployment is hindered by channel disturbances like polarization fluctuations.
• Environmental changes can cause intermittent failures in existing QKD systems.

Purpose of the Study:

• To propose a high-speed Faraday-Sagnac-Michelson QKD system.
• To develop a system capable of automatically compensating for channel polarization disturbance.
• To overcome the intermittency limitations caused by environmental mutations in QKD.

Main Methods:

• Implementation of a phase-coding QKD system using a Faraday-Sagnac-Michelson interferometer.
• Testing the system over a 50 km fiber channel with induced 30 Hz polarization scrambling.
• Characterization of system performance, including interference fringe visibility and secure key rate.

Main Results:

• Achieved high interference fringe visibility of 99.35% over a 24-hour period.
• Demonstrated a stable secure key rate of 306 kb/s sustained over seven days.
• The system operated without the need for active polarization alignment, showcasing robustness.

Conclusions:

• The proposed Faraday-Sagnac-Michelson QKD system effectively compensates for channel polarization disturbance.
• This robust system overcomes environmental limitations, enabling practical and stable secure communication.
• The technology facilitates reliable, high-speed quantum key distribution in real-world fiber channels.