Direct intensity and phase modulation for quantum key distribution transmitters

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Optical Engineering

Background:

• Decoy-state quantum key distribution (QKD) is vital for security against photon-number-splitting attacks.
• External modulators in QKD systems introduce security vulnerabilities.
• Practical QKD requires robust, secure, and simplified transmitter designs.

Purpose of the Study:

• To develop a secure QKD system using a directly modulated light source.
• To eliminate external modulators for enhanced security and reduced complexity.
• To achieve high-speed, long-distance QKD with practical security guarantees.

Main Methods:

• Utilized optical injection locking for a directly modulated light source.
• Generated simultaneous intensity- and phase-modulated signals without external modulators.
• Implemented a high-speed phase-encoding BB84 protocol with an optimized one-decoy strategy and finite-size analysis.

Main Results:

• Achieved positive key rates up to 20 dB channel loss (100 km fiber).
• Successfully integrated commercial InGaAs single-photon detectors.
• Demonstrated enhanced security by removing modulator-induced side-channels.

Conclusions:

• The proposed directly modulated light source significantly enhances QKD security.
• The system offers reduced transmitter complexity for practical QKD applications.
• This approach paves the way for more secure and implementable QKD networks.