An international research team including scientists from Paderborn University has achieved a milestone in the quest for a quantum internet. For the first time, researchers have successfully teleported the polarization state of a single photon between two physically separate quantum dots over a 270-meter free-space optical link. The findings have been published in the journal Nature Communications.

A Decade of Work

At Paderborn University, doctoral and postdoctoral researchers spent approximately ten years working on optical measurements, data analysis, and evaluation. During this time, Professor Klaus Jöns’s group collaborated closely with a team led by Professor Rinaldo Trotta at Sapienza University of Rome.

“The experiment impressively demonstrates that quantum light sources based on semiconductor quantum dots could serve as a key technology for future quantum communication networks,” Jöns said. “Successful quantum teleportation between two independent quantum emitters represents a vital step towards scalable quantum networks.”

Technical Breakthrough

Quantum entanglement systems link multiple quantum particles, allowing them to share information states. Previously, photons used for quantum communication came from a single emission source. While significant progress has been made in recent years using independent light sources, this experiment marks the first use of two completely independent quantum dots as emitters.

Professors Jöns and Trotta outlined their plan to use quantum dots as sources of entangled photon pairs for communication and teleportation systems about ten years ago. The success of this experiment validates the correctness of that long-term strategic direction.

“This result shows that our long-term strategic planning has paid off,” Jöns said. “The combination of excellent materials science, nanofabrication and optical quantum technology was the key to our success.”

Europe-Wide Collaboration

The breakthrough relied on contributions from multiple research centers across Europe. Quantum dots were precisely engineered at Johannes Kepler University Linz in Austria, resonator nanofabrication was carried out by partners at the University of Würzburg in Germany, and the teleportation experiments themselves took place in Rome.

The system used GPS-assisted synchronization, ultra-fast single-photon detectors, and stabilization methods to counter atmospheric turbulence. The achieved teleportation state fidelity — the quality with which quantum states are preserved during teleportation — reached up to 82 ± 1%, exceeding the classical communication limit threshold.

Next Step: Quantum Relays

This accomplishment opens the door to demonstrating “entanglement swapping” between two quantum dots. Achieving this would create the first quantum relay using two deterministic sources of entangled photon pairs. Deterministic sources can reliably produce single photons on demand, a key element for building practical quantum networks.

Almost simultaneously, another research team from Stuttgart and Saarbrücken reported a similar achievement using frequency conversion. Together, these results mark a significant milestone for quantum research in Europe and bring the vision of a functional quantum internet closer to reality.

Source: ScienceDaily