Time-bin phase-encoding quantum key distribution using Sagnac-based optics and compatible electronics.

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Optical Communication Systems

Background:

• Quantum Key Distribution (QKD) offers secure communication by leveraging quantum mechanics principles.
• Existing QKD schemes often face challenges with environmental stability and complex calibration requirements.
• Time-bin encoding is a promising QKD protocol, but its practical implementation requires robust and stable setups.

Purpose of the Study:

• To introduce a novel time-bin phase-encoding quantum key distribution (QKD) system.
• To demonstrate a QKD scheme that is inherently stable and insensitive to environmental disturbances.
• To showcase the practical performance and applicability of this new QKD approach.

Main Methods:

• Utilized a transmitter with an inherently stable Sagnac-type interferometer for time-bin phase encoding.
• Employed a compact QKD system for experimental validation.
• Simulated channel loss using variable optical attenuators to assess performance under different conditions.
• Conducted a 9-day continuous test over a 120-km fiber spool.

Main Results:

• Achieved a secure key rate of 6.2 kbps at 20 dB channel loss and 0.4 kbps at 30 dB channel loss.
• Demonstrated a stable quantum bit error rate (QBER) within 0.4%–0.6% for the time-bin basis over 9 days on a 120-km fiber spool.
• The system requires comparable electrical power to existing polarization or phase encoding schemes and does not need intensity calibration.

Conclusions:

• The presented time-bin phase-encoding QKD scheme offers intrinsic stability and high performance.
• The Sagnac interferometer-based approach eliminates the need for intensity calibration and reduces sensitivity to environmental factors.
• This robust and compatible QKD scheme is suitable for various applications, including BB84 and measurement-device-independent QKD (MDI-QKD).