Four researchers from the Institute of Photonics at Leibniz University Hannover have created a new transmitter-receiver system for sending entangled photons through an optical fiber. This could pave the way for the next generation of telecommunications technology, the quantum Internet, to use optical fibers. The quantum Internet offers encryption methods that are secure from eavesdropping, even by future quantum computers, protecting critical infrastructure.

“To make the quantum Internet a reality, we need to transmit entangled photons via fiber optic networks,” says Prof. Dr. 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 showed that photon entanglement remains intact even when sent 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 Philip Rübeling, a doctoral student at the Institute of Photonics researching the quantum Internet. “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 combine the traditional Internet with the quantum Internet. So far, using both transmission methods per color in an optical fiber has not been possible.

“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.

The experiment showed for the first time that photons can be sent in the same color channel as the laser light. This means all color channels can still be used for regular data transmission.