Long-distance entanglement-based quantum key distribution over optical fiber.

Area of Science:

• Quantum Information Science
• Quantum Communication
• Optoelectronics

Background:

• Quantum key distribution (QKD) offers enhanced security over classical cryptography.
• Entanglement-based QKD leverages quantum entanglement for secure key generation.
• Extending QKD distances is crucial for practical, widespread adoption.

Purpose of the Study:

• To demonstrate the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber.
• To evaluate the feasibility and performance of entanglement-based QKD at extended distances.
• To showcase the integration of advanced quantum technologies for secure communication.

Main Methods:

• Utilized superconducting single photon detectors (NbN nanowires) for high-speed detection in the 1.5-μm telecom band.
• Employed an efficient entangled photon pair source featuring a fiber-coupled periodically poled lithium niobate waveguide and ultra-low loss filters.
• Integrated planar lightwave circuit Mach-Zehnder interferometers (MZIs) for ultra-stable operation.

Main Results:

• Successfully performed an entanglement-based QKD experiment over a 100-km optical fiber.
• Generated a 16 kbit sifted key during an approximately 8-hour experiment.
• Achieved a quantum bit error rate (QBER) of 6.9% at a rate of 0.59 bits per second.
• Distilled a 3.9 kbit secure key from the generated sifted key.

Conclusions:

• Entanglement-based QKD is feasible over 100-km optical fiber links.
• The developed system components (detectors, sources, MZIs) enable high-performance QKD at telecom wavelengths.
• This work represents a significant step towards long-distance, secure quantum communication networks.