Deutsche Telekom Innovation Laboratories (T-Labs) and quantum networking company Qunnect successfully demonstrated the sustained delivery of entangled photons over 30 kilometers (18.6 miles) of commercially deployed fiber infrastructure in Berlin. The 17-day experiment maintained 99% fidelity with only 1% downtime, marking a significant milestone toward real-world deployment of the quantum internet. The results were presented on March 31, 2025, at the OFC conference in San Francisco.
The system operated within Deutsche Telekom’s existing fiber-optic network and automatically compensated for environmental changes, enabling stable polarization entanglement over extended periods. In a second field trial, the researchers routed entangled photons across 82 kilometers (50.9 miles) while running classical data traffic in parallel. This dual-use configuration, with entangled photons in the O-band and classical signals in the C-band, achieved over 92% fidelity, setting a new benchmark for entanglement distribution in real-world telecom environments.
The companies say these breakthroughs validate the compatibility of polarization-based qubits with commercial fiber infrastructure and underline their potential for use in quantum key distribution, satellite synchronization, and industrial sensing. T-Labs’ Berlin-based Quantum Lab, launched in 2023 and linked to a 2,000-kilometer network, serves as the platform for this work, in collaboration with academic and industrial partners including Qunnect, Fraunhofer HHI, and multiple German universities.
- T-Labs and Qunnect sustained 99% fidelity entanglement over 30 km of commercial fiber for 17 days.
- Second test distributed entanglement over 82 km while coexisting with classical data traffic.
- First time a major telecom provider has run entanglement experiments over its own production fiber network.
- Experiments used polarization qubits, compatible with quantum computers and sensors but challenging to stabilize in fiber.
- Work conducted at Deutsche Telekom’s Berlin Quantum Lab, opened in 2023 and linked to a 2,000 km research fiber backbone.
“We are grateful to T-Labs and Deutsche Telekom for the opportunity to showcase the performance of our products integrated with classical data traffic over commercial network infrastructure. Such partnerships are critical for demonstrating the progress towards commercial utility of quantum networking,” said Noel Goddard, CEO of Qunnect.