02 Dez. Quantum dots for the practical implementation of the quantum internet
An international research team involving the University of Paderborn reports a decisive breakthrough on the path to the quantum internet: The researchers have succeeded in teleporting the polarization state of a single photon emitted by one quantum dot to a photon emitted of another – spatially separated – quantum dot. This means that the property of one photon could be transferred to another. According to the researchers, this step is particularly important for future quantum communication networks. In their experiments, the scientists used, among other things, a 270 m long free-space connection.
Quantum relays form the basis of the quantum internet
When entangled systems consisting of several quantum particles are used instead of a single state, such as a single photon, the result is an overall system consisting of several states. Such systems are used in communication, data security, and quantum computing. Entanglement involves coupling certain properties of the photons with each other. Each state corresponds to a piece of information that is further processed. “Until now, however, these photons came from one and the same source, i.e., the same emitter,” explains Professor Klaus Jöns, head of the Hybrid Photonics Quantum Devices working group and member of the board of the Institute for Photonic Quantum Systems (PhoQS) at the University of Paderborn. “Although there has been considerable progress in recent years, the use of different quantum emitters to realize a quantum relay between distant parties has been unattainable until now.”
Over a period of about three years, Jöns‘ team says it has been intensively engaged in optical measurements, data evaluation, and analysis. The Paderborn group collaborated with the team of Professor Rinaldo Trotta from Sapienza University of Rome, Italy. Jöns explains: „The experiment impressively demonstrates that quantum light sources based on semiconductor quantum dots are a key technology for future quantum communication networks. Successful quantum teleportation between two different quantum emitters is a significant step toward scalable quantum relays and thus the practical implementation of the quantum internet.
European project cooperation
According to Jöns and Trotta, they developed a roadmap more than ten years ago for how quantum dots can be used as sources of entangled photon pairs for quantum communication and teleportation protocols. “This result shows that our long-term strategic planning has paid off,” says Jöns. “The combination of excellent materials science, nanofabrication, and optical quantum technology was the key to success.”
The quantum dots were developed at Johannes Kepler University Linz. The resonators were nanofabricated by partners at the University of Würzburg. Researchers at Sapienza University of Rome conducted the quantum teleportation experiments, including a 270 m long free-space connection between two university buildings. GPS-based synchronization, ultra-fast single-photon detectors, and active stabilization systems compensated for atmospheric turbulence. The achieved teleportation fidelity of 82 ± 1%, i.e., the degree to which quantum states are preserved during teleportation, exceeds the classical limit by more than ten standard deviations, according to the results.
Outlook: First quantum relay with two deterministic sources
According to the research partners, this success has paved the way for the next major milestone: the demonstration of ‚entanglement swapping‘ between two quantum dots. This is expected to be the first quantum relay with two deliberately generated sources of entangled photon pairs.
Parallel developments
Independently and almost simultaneously, a research team from Stuttgart and Saarbrücken achieved a similar result using frequency conversion. Together, these two studies mark an important milestone for European quantum research.
Original publication:
[Laneve, A., Ronco, G., Beccaceci, M. et al.: Quantum teleportation with dissimilar quantum dots over a hybrid quantum network; Nat Commun 16, 10028, 2025, https://doi.org/10.1038/s41467-025-65911-9]
Source: www.uni-paderborn.de
Image: Besim Mazhiqi / University of Paderborn