A team of researchers in Germany has achieved a breakthrough that pushes the dream of a quantum internet closer to reality. Scientists at the University of Stuttgart have successfully transferred quantum information between photons emitted by two separate quantum dots, marking the first time this has ever been done.
The challenge at the heart of long distance quantum communication is that single photons weaken in optical fibers, and unlike classical signals, quantum information cannot be copied or amplified. Quantum repeaters are supposed to solve that by using teleportation to refresh the signal, but that technique only works if the photons from different sources are nearly identical. Producing such twins on demand has been one of the biggest obstacles in the field.
Quantum dots offer a possible solution. These nanoscale semiconductor structures emit single photons with predictable properties based on their fixed energy levels. Working with the Leibniz Institute for Solid State and Materials Research in Dresden, the Stuttgart team used two nearly identical quantum dots to generate the photons needed for their experiment.
One dot created a single photon, while the other produced an entangled pair. One photon from that pair traveled through a 10 meter fiber and interfered with the single photon. That interaction transferred the quantum state to the distant partner photon, achieving the teleportation step required for quantum repeaters. Quantum frequency converters from Saarland University smoothed out the last remaining frequency differences so the photons behaved as though they came from the same source.
The experiment reached a teleportation success rate just over 70 percent, and the team aims to improve it by stabilizing the quantum dots and refining semiconductor fabrication techniques. Earlier work from the same group has already shown that quantum entanglement can survive a 36 kilometer fiber line across Stuttgart, suggesting the system can scale.
The project is part of Germany’s Quantenrepeater.Net initiative, which brings together dozens of partners to build quantum repeater technology compatible with today’s fiber networks. Researchers say the result marks a major milestone, turning what was once purely theoretical into a practical building block for future quantum communication systems.