Hyperentanglement-enabled noise-resilient quantum communication over a 40 km intra-city fiber network

Entanglement distribution over deployed fiber links is essential for implementing quantum communication protocols. However, environmental noise in deployed fibers, such as classical signals, stray light, and Raman scattering, can significantly degrade entanglement, ultimately destroying the nonlocal correlations required for quantum communication. In this work, we demonstrate noise-resilient quantum communication over 40 km of intra-city deployed fiber, with a total transmission loss of 23.04 dB, by utilizing hyperentanglement in the time-bin and frequency degrees of freedom. By exploiting the frequency anticorrelation of the photon pairs and implementing frequency-to-time mapping using dense wavelength-division multiplexing combined with calibrated delay lines, we realize frequency-resolved detection that discriminates frequency-anticorrelated entangled photon pairs from uncorrelated noise. This enables reliable entanglement distribution with over an order-of-magnitude improvement in signal-to-noise ratio and a substantial increase in Bell-state fidelity, even in high-noise and high-loss conditions of deployed fibers. Moreover, entanglement—initially lost due to entanglement sudden death—is successfully restored, enabling a clear violation of the Bell inequality. These results establish a practical and scalable method for entanglement distribution in noisy and lossy environments, advancing the feasibility of real-world quantum communication over existing fiber infrastructure.