Phase encoded quantum key distribution up to 380 km in standard telecom grade fiber enabled by baseline error...

Area of Science:

• Quantum Information Science
• Optical Communication Systems
• Cryptography

Background:

• Phase encoding in quantum key distribution (QKD) is crucial for secure, long-distance communication.
• Practical QKD systems face errors from laser linewidth, detector dark counts, and channel dispersion.

Purpose of the Study:

• To develop a theoretical model for characterizing and mitigating errors in phase encoding QKD systems.
• To optimize optical pulse parameters for reduced distortion and improved QKD performance.

Main Methods:

• Developed a novel theoretical model for phase encoding QKD error analysis.
• Implemented the model to a differential phase shift (DPS) QKD scheme.
• Analyzed system performance with varying detector parameters and fiber types.

Main Results:

• Achieved a secure key rate of 193 bits/s at 265 km with QKD.
• Demonstrated an unprecedented QBER < 1% up to 225 km using standard telecom components.
• Established secure keys up to 380 km with standard fiber and 432 km with ultra-low-loss fiber.

Conclusions:

• The theoretical model effectively reduces system imperfections and lowers the quantum bit error rate (QBER).
• The optimized QKD system is compatible with existing fiber networks, enabling long-distance, secure communication.
• The findings are applicable to various fiber-based phase and time encoding protocols.