An international team of researchers has achieved a milestone in quantum communication by teleporting the polarization state of a single photon between two separate quantum dots over a 270-meter open-air link. The experiment, conducted at Sapienza University of Rome, demonstrates the potential for quantum relays in future quantum networks. The findings were published in Nature Communications.
Researchers from Paderborn University, Sapienza University of Rome, and other European institutions successfully transferred quantum information between independent quantum dots. They used a 270-meter free-space optical link connecting two buildings at Sapienza University of Rome, employing GPS-assisted synchronization, ultra-fast single-photon detectors, and stabilization against atmospheric turbulence. The teleportation achieved a state fidelity of 82 ± 1%, surpassing the classical limit by more than 10 standard deviations. Quantum dots were engineered at Johannes Kepler University Linz, with resonator nanofabrication at the University of Würzburg. Professor Klaus Jöns of Paderborn University, head of the Hybrid Photonics Quantum Devices group, stated: “The experiment impressively demonstrates that quantum light sources based on semiconductor quantum dots could serve as a key technology for future quantum communication networks.” This breakthrough, after a decade of collaboration between Jöns's team and Professor Rinaldo Trotta's group at Sapienza, marks progress toward scalable quantum relays and a quantum internet. Previously, such teleportation involved photons from the same source, but this used distinct emitters. Jöns noted: “This result shows that our long-term strategic planning has paid off. The combination of excellent materials science, nanofabrication and optical quantum technology was the key to our success.” The achievement opens the path to entanglement swapping between quantum dots, enabling the first quantum relay with deterministic entangled photon pair sources. A parallel effort by teams from Stuttgart and Saarbrücken reported a similar result using frequency conversion.