Light quanta in fibre optic networks: researchers make progress in beaming in Berlin

Researchers in Berlin have made a significant breakthrough in quantum communication by successfully demonstrating the teleportation of quantum information through a commercial urban fiber-optic network. The experiment, conducted by scientists from the University of Paderborn, Germany's Deutsche Telekom, and the American network equipment manufacturer Qunnect, marks a critical step toward building a secure quantum internet. The team used a 30-kilometer section of Berlin’s existing fiber-optic infrastructure to transmit quantum states over long distances using a process known as quantum teleportation, often referred to colloquially as “beaming.” The researchers transmitted photons with a standard telecommunications wavelength of 1324 nanometers through the fiber network. These photons were entangled with other photons of a shorter wavelength (795 nanometers), which remained local to the experiment site. By combining these entangled photons with additional laser photons via a partially transparent mirror, the team initiated the teleportation process. This allowed the quantum state of the laser photons to be instantly transferred to the photons traveling through the city’s fiber-optic cables. At the end of the fiber link, specialized detectors confirmed the successful transfer of the quantum state in approximately 90 percent of cases. The findings were published on the preprint server arXiv. The central hub of the teleportation experiment was the Quantum Lab at Deutsche Telekom’s facility in Berlin. According to Matheus Sena, one of the lead researchers, the team tested the quality of teleportation under varying environmental conditions. On shorter distances of several kilometers, the teleported quantum state was preserved with an average probability of 92 percent. Even over the full 30-kilometer distance, the fidelity of the transmission remained at 90 percent. When conventional telecommunications signals were also sent through the same fiber optic cable alongside the quantum signal, the transmission quality dropped slightly to 86 percent. Sena emphasized that the results of their experiments provide compelling evidence of the potential of quantum teleportation for practical applications in quantum communication. He noted that successful quantum teleportation is typically defined as achieving more than 67 percent fidelity. For real-world applications such as exchanging quantum keys, the researchers aim to improve their method further. Their goal is to achieve transmission fidelities of 98 percent or higher. The implications of this research extend beyond theoretical physics into practical applications aimed at securing critical infrastructure. The ultimate objective is to connect essential institutions such as data centers, banks, energy providers, hospitals, and government agencies using quantum technology to protect them against unauthorized access. Additionally, linking quantum sensors and quantum computers to create more powerful computing systems is another key focus area. While numerous test routes already exist across Europe to explore secure data transmission using quantum cryptography, most of these are special-purpose fiber connections established specifically for experimental purposes. In Germany alone, there are more than twenty such quantum links. However, until now, these have primarily been dedicated fiber lines between universities and research institutes rather than part of a broader commercial network. The recent success in Berlin demonstrates that quantum information can be reliably transmitted within a commercial urban data network, opening new possibilities for integrating quantum communication technologies into existing infrastructure. The team’s work highlights the feasibility of deploying quantum teleportation in real-world environments, moving closer to the vision of a fully functional quantum internet. As they continue refining their techniques, the prospect of widespread implementation becomes increasingly tangible, promising enhanced security and performance in future communication networks.