Coexistence of Continuous-Variable Quantum Key Distribution and Classical Data over 120 km Fiber

Area of Science:

• Quantum Information Science
• Optical Communications
• Cybersecurity

Background:

• Integrating quantum key distribution (QKD) with classical data on shared fibers is essential for scalable quantum security.
• Classical channel noise significantly limits the distance achievable for QKD systems.

Purpose of the Study:

• To demonstrate the longest possible distance for continuous-variable QKD (CV-QKD) coexisting with classical traffic.
• To assess the feasibility of CV-QKD for deployment in existing long-haul optical networks.

Main Methods:

• Demonstrated CV-QKD over 120 km fiber with 20 dB loss in the asymptotic regime and 100 km with 17 dB loss in the finite-size regime.
• Achieved coexistence with a fully populated coarse wavelength division multiplexing (CWDM) system.
• Utilized natural mode filtering of the local oscillator and phase noise mitigation without extra filtering or wavelength reallocation.

Main Results:

• Achieved a record fiber distance for CV-QKD, surpassing previous limitations.
• Demonstrated successful integration and operation alongside a dense classical WDM system.
• Confirmed feasibility for 80-100 km long-haul networks through benchmarking and finite-size analysis.

Conclusions:

• CV-QKD can be implemented over record distances, even with significant fiber loss and coexisting classical signals.
• The system offers a plug-and-play solution suitable for current optical network infrastructure.
• Results highlight the potential for cost-effective, large-scale quantum-secured communication deployment.