Four researchers from the Institute of Photonics at Leibniz University Hannover have developed a new trans­mitter-receiver concept for trans­mitting entangled photons over an optical fiber. This breakthrough could enable the next generation of telecommuni­cations technology, the quantum Internet, to be routed via optical fibers. The quantum Internet promises eaves­dropping-proof encryption methods that even future quantum computers cannot decrypt, ensuring the security of critical infra­structure.

“To make the quantum Internet a reality, we need to transmit entangled photons via fiber optic networks,” says Michael Kues, Head of the Institute of Photonics and Board Member of the PhoenixD Cluster of Excellence at Leibniz University Hannover. “We also want to continue using optical fibers for conven­tional data trans­mission. Our research is an important step to combine the conventional Internet with the quantum Internet.”

In their experiment, the researchers demonstrated that the entangle­ment of photons is maintained even when they are sent together with a laser pulse. “We can change the color of a laser pulse with a high-speed electrical signal so that it matches the color of the entangled photons,” explains doctoral student Philip Rübeling. “This effect enables us to combine laser pulses and entangled photons of the same color in an optical fiber and separate them again.”

This effect could integrate the conventional Internet with the quantum Internet. Until now, it has not been possible to use both trans­mission methods per color in an optical fiber. “The entangled photons block a data channel in the optical fiber, preventing its use for conventional data transmission,” says Jan Heine, a doctoral student in Kues' group.

With the concept demonstrated for the first time in the experiment, the photons can now be sent in the same color channel as the laser light. This implies that all color channels could still be used for conventional data trans­mission. “Our experiment shows how the practical implemen­tation of hybrid networks can succeed,” says Michael Kues. (Source: U. Hannover)

Reference: P. Rübeling et al.: Quantum and coherent signal transmission on a single-frequency channel via the electro-optic serrodyne technique, Sci. Adv. 10, adn8907 (2024); DOI: 10.1126/sciadv.adn8907

Link: Cluster of Excellence PhoenixD (Photonics, Optics, and Engineering - Innovation Across Disciplines), Leibniz University Hannover, Hannover, Germany