Ultrabright Entanglement Based Quantum Key Distribution over a 404 km Optical Fiber

TL;DR

This paper reports a highly efficient polarization-entangled photon source used for long-distance quantum key distribution over 404 km of optical fiber, demonstrating practical quantum communication capabilities.

Contribution

The authors develop an ultrabright, wavelength-multiplexed entangled photon source optimized for long-distance quantum key distribution in fiber networks.

Findings

Achieved secure key rates up to 440.80 bits/s over 200 km

Extended secure quantum communication distance to 404 km

Demonstrated practical implementation with high photon pair generation rate

Abstract

Entangled photons are crucial resources for quantum information processing. Here, we present an ultrabright polarization-entangled photon source based on a periodically poled lithium niobate waveguide designed for practical quantum communication networks. Using a 780 nm pump laser, the source achieves a pair generation rate of 2.4 $\times 10^{10}$ pairs/s/mW. Remarkably, the entangled photons are bright enough to be detected by a power meter, reaching a power of 17.9 nW under a pump power of 3.2 mW. We demonstrate the practicality of the source by conducting quantum key distribution experiments over long-distance fiber links. Wavelength-division multiplexing was employed to enhance the key generation, and nonlocal dispersion compensation was implemented to ensure precise timing coincidence measurements across a broad spectral range. By utilizing nine pairs of wavelength channels, the system achieved the applicable secure key rates of up to 440.80 bits/s over 200 km with a 62 dB loss and extended the maximum secure key generation distance to 404 km. These results demonstrate the potential of wavelength-multiplexed polarization-entangled photon sources for high-speed, long-distance quantum communication, positioning them as key components for future large-scale quantum networks.