While the cointegration of quantum frequency-entangled with coherent information transmission can be achieved via spectral multiplexing, more resource-efficient approaches are required in order to accommodate the next generation of telecommunications technology, the quantum internet. Researchers from Leibniz University Hannover have sent entangled photons and laser pulses of the same color over a single optical fiber. According to the researchers, this is the first time the feat has been achieved. The team developed a new transmitter-receiver concept for transmitting entangled photons over an optical fiber. The work could enable the next generation of telecommunications technology, the quantum internet, to be routed via optical fibers. (From left) Researchers Jan Heine, Philip Rübeling, Michael Kues, and Robert Johanning have developed a concept to enable the cohabitation of quantum and conventional internet signals in the same optical fiber without the need to multiplexing. Courtesy of Leibniz University Hannover. “To make the quantum internet a reality, we need to transmit entangled photons via fiber optic networks,” said 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. The concept leverages the serrodyne technique, which applies a linear temporal phase ramp to translate the spectrum of an optical pulse via electro-optical phase modulation, leading to very different dynamics for entangled and coherent photons. This enables temporal multiplexing of the respective signals. “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,” said Philip Rübeling, a doctoral student researching the quantum internet at the Institute of Photonics. “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, the team said, 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,” said 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,” said Kues. The research was published in Science Advances (www.doi.org/10.1126/sciadv.adn8907).
