Sub-Mbps key-rate continuous-variable quantum key distribution with local local oscillator over 100-km fiber

Area of Science:

• Quantum Information Science
• Quantum Communication
• Cryptography

Background:

• Continuous-variable quantum key distribution (CV-QKD) offers enhanced security over classical methods.
• Achieving long-distance and high-speed CV-QKD remains a significant challenge due to noise and signal degradation.
• Gaussian-modulated coherent-state (GMCS) protocols are a promising avenue for practical CV-QKD.

Purpose of the Study:

• To experimentally demonstrate a GMCS CV-QKD system with improved transmission distance and secure key rate.
• To investigate methods for mitigating excess noise and compensating for channel impairments in CV-QKD.
• To assess the feasibility of long-distance, high-speed quantum key distribution.

Main Methods:

• Co-transmission of quantum signals and pilot tones using wideband frequency and polarization multiplexing.
• Implementation of a data-assisted time domain equalization algorithm to compensate for phase noise and polarization variations.
• Experimental setup for a GMCS CV-QKD system operating over a 100-km fiber channel.

Main Results:

• Demonstrated a sub-megabit per second (Mbps) key rate CV-QKD over 100 km.
• Achieved asymptotic secure key rates of 7.55 Mbps (50 km), 1.87 Mbps (75 km), and 0.51 Mbps (100 km).
• Significantly improved transmission distance and secure key rate compared to existing GMCS CV-QKD experiments.

Conclusions:

• The developed CV-QKD system shows substantial advancements in distance and speed.
• The employed noise mitigation and equalization techniques are effective for long-distance quantum communication.
• This work highlights the potential for practical, long-haul, high-speed secure quantum key distribution.