Deutsche Telekom Innovation Laboratories (T-Labs), in collaboration with Qunnect, has demonstrated stable polarization-entangled photon transmission across 30 kilometers of commercially deployed optical fiber for 17 consecutive days, maintaining 99% fidelity and 99% uptime. The test was conducted on T-Labs’ infrastructure in Berlin, forming part of its quantum research program aimed at validating quantum networking capabilities using real-world telecom environments. The results were first presented at the OFC Conference in San Francisco on March 31, 2025.
In a separate experiment, polarization-entangled photons were dynamically routed over fiber paths totaling 82 kilometers while coexisting with classical data traffic. Conducted in the O-band and multiplexed with C-band data, the system achieved fidelities above 92%, representing the longest high-fidelity entanglement distribution over commercial infrastructure in this configuration to date. The findings are currently available on arXiv, marking a significant advancement toward integrating quantum communication into classical networks.
The experiments demonstrated that existing telecom-grade infrastructure can support polarization qubits—a qubit type compatible with quantum computers, sensors, and memories—despite previous challenges in stabilizing them across fiber. The long-term stability achieved is a prerequisite for quantum internet applications beyond secure point-to-point communication, including quantum key distribution, precision time synchronization, and quantum-enhanced sensing. These capabilities are expected to support future enterprise and industrial applications.
T-Labs’ broader research strategy focuses on embedding quantum technologies into communication systems and driving innovation through cooperation with institutions including Fraunhofer HHI and technical universities in Berlin, Dresden, and Munich. Its Quantum Lab, opened in 2023 in Berlin, connects to a 2,000 km national fiber network and serves as the experimental foundation for testing quantum communication technologies in operational settings. Qunnect, based in the US and Netherlands, provides integrated hardware solutions for quantum networking and previously launched the Gotham Rack, a commercial entanglement system for fiber-based networks.
Read the full announcement from Deutsche Telekom here and access the full technical paper on arXiv here.
April 15, 2025
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