Adaptive-sign CMA for continuous-variable quantum key distribution under high-speed polarization disturbances

Area of Science:

• Optics and Photonics
• Quantum Information Science
• Telecommunications Engineering

Background:

• Polarization fluctuations in long-distance single-mode fiber optic cables disrupt classical and quantum communication systems.
• Maintaining signal integrity is crucial for secure data transmission, especially in quantum key distribution (QKD).

Purpose of the Study:

• To develop an efficient and low-complexity algorithm for polarization recovery in fiber optic systems.
• To enhance the performance and resilience of continuous-variable quantum key distribution (CV-QKD) systems against polarization disturbances.

Main Methods:

• Proposing an adaptive-sign constant modulus algorithm (AS-CMA) with an error-driven adaptive step size.
• Implementing a sign-based weight update mechanism to reduce computational complexity compared to conventional CMA.
• Validating the AS-CMA algorithm within a simulated continuous-variable quantum key distribution (CV-QKD) system.

Main Results:

• AS-CMA demonstrated robust polarization recovery under simulated polarization disturbance rates of up to 10 Mrad/s over 25 km of single-mode fiber, with only a 12.9% decrease in secret key rate.
• The algorithm maintained a positive secret key rate even under extreme transient disturbances of 43 Mrad/s, simulating lightning events.
• Significant reduction in computational complexity was achieved compared to traditional CMA methods.

Conclusions:

• The AS-CMA offers an efficient and computationally inexpensive solution for polarization recovery in CV-QKD systems.
• This algorithm enhances the reliability and security of quantum communication networks operating over long-distance fiber optic links.
• AS-CMA shows promise for practical implementation in future secure communication infrastructures.