Scientists just teleported information using light

Their study appears in Nature Communications.

Quantum Dots as Tiny Platforms for Information Transfer

"For the first time worldwide, we have succeeded in transferring quantum information among photons originating from two different quantum dots," says Prof. Peter Michler, head of the IHFG and deputy spokesperson for the Quantenrepeater.Net (QR.N) research project. To understand why this matters, it helps to look at how communication works. Whether someone sends a WhatsApp message or streams a video, the data always relies on zeros and ones. Quantum communication follows a similar idea, but individual photons act as the information carriers. A zero or one is encoded through the direction of the photon's polarization (i.e., their orientation in the horizontal and vertical directions or in a superposition of both states). Because photons behave according to quantum mechanics, their polarization cannot be measured without leaving detectable traces. Any attempt to intercept the message would be exposed.

Preparing Quantum Networks for Fiber Optics

Another critical issue involves compatibility with today's internet infrastructure. An affordable quantum internet would rely on the same optical fibers used now. However, light traveling through fiber can be transmitted only over limited distances. Conventional signals are refreshed roughly every 50 kilometers using an optical amplifier. Quantum information cannot be amplified or copied, which means this approach does not work. Instead, quantum physics makes it possible to transfer information from one photon to another as long as the information itself remains unknown. This phenomenon is called quantum teleportation.

Developing Quantum Repeaters for Long-Distance Transfer

To take advantage of quantum teleportation, scientists are designing quantum repeaters that can renew quantum information before it disappears in the fiber. These repeaters would function as essential nodes in a quantum internet. Creating them has been difficult. Teleportation requires the photons to be nearly identical in properties such as timing and color. Producing such photons is hard because they come from separate sources. "Light quanta from different quantum dots have never been teleported before because it is so challenging," says Tim Strobel, scientist at the IHFG and first author of the study.

As part of QR.N, his team developed semiconductor light sources that emit photons that closely match each other. "In these semiconductor islands, certain fixed energy levels are present, just like in an atom," says Strobel. This setup enables the production of individual photons with well-defined characteristics. "Our partners at the Leibniz Institute for Solid State and Materials Research in Dresden have developed quantum dots that differ only minimally," he adds. This makes it possible to generate nearly identical photons in two separate locations.

Teleporting Information Between Photons From Different Sources

At the University of Stuttgart, the researchers successfully teleported the polarization state of a photon from one quantum dot to a photon produced by a second quantum dot. One dot emits a single photon and the other generates an entangled photon pair. "Entangled" means the two photons share a single quantum state even when physically apart. One photon from the pair travels to the second quantum dot and interacts with its photon. When the two overlap, their superposition transfers the information from the original photon to the far-away partner of the entangled pair.

A key element of this achievement was the use of "quantum frequency converters," devices that adjust small frequency mismatches between photons. These converters were designed by a team led by Prof. Christoph Becher, a quantum optics specialist at Saarland University.

Working Toward Longer Distances and Higher Accuracy

"Transferring quantum information between photons from different quantum dots is a crucial step toward bridging greater distances," Michler explains. In this experiment, the two quantum dots were linked by about 10 meters of optical fiber. "But we are working on achieving considerably greater distances," says Strobel.

Earlier research had already shown that entanglement between quantum dot photons can survive a 36-kilometer transmission through the city center of Stuttgart. The team also aims to increase the teleportation success rate, which is currently a little above 70%. Variations within each quantum dot still cause small inconsistencies in the photons.

"We want to reduce this by advancing semiconductor fabrication techniques," says Strobel. Dr. Simone Luca Portalupi, group leader at the IHFG and one of the study coordinators, adds, "Achieving this experiment has been a long-standing ambition -- these results reflect years of scientific dedication and progress. It's exciting to see how experiments focused on fundamental research are taking their first steps toward practical applications."

A Nationwide Effort to Build Quantum Repeater Technology

Research on quantum repeaters receives funding from the Federal Ministry of Research, Technology and Space (BMFTR) as part of the "Quantenrepeater.Net (QR.N)" project. Coordinated by Saarland University, the QR.N network includes 42 partners from universities, research institutes, and industry who collaborate on developing and testing quantum repeater technology in optical fiber networks. The program builds on results from the earlier "Quantenrepeater.Link (QR.X)" initiative, also supported by the BMFTR (formerly BMBF), which helped lay the foundation for a nationwide quantum repeater from 2021 to 2024. Scientists at the University of Stuttgart have played a central role in both efforts.

The quantum teleportation experiments were carried out under the leadership of the Institute of Semiconductor Optics and Functional Interfaces (IHFG) with contributions from the Leibniz Institute for Solid State and Materials Research (IFW) in Dresden and the Quantum Optics research group at Saarland University.