December 02, 2025 -- An international research team involving Paderborn University has achieved a crucial breakthrough on the road to a quantum internet: for the first time ever, the polarisation state of a single photon emitted from a quantum dot was successfully teleported to another, physically separated quantum dot. In simpler terms, this means that the properties of one photon can be transmitted to another via teleportation. This is a particularly vital step for future quantum communication networks. For example, the scientists used a 270m free-space optical link for their experiments. The results have now been published in the specialist journal Nature Communications.

Long-term European collaboration brings success

A team of doctoral and postdoctoral students at Paderborn University have spent approximately ten years focusing on optical measurements, data evaluation and analysis. As part of this, Professor Klaus Jöns's Paderborn group has been working with the team led by Professor Rinaldo Trotta at the Sapienza University of Rome in Italy. ‘The experiment impressively demonstrates that quantum light sources based on semiconductor quantum dots could serve as a key technology for future quantum communication networks. Successful quantum teleportation between two independent quantum emitters represents a vital step towards scalable quantum relays and thus the practical implementation of a quantum internet’, explained Professor Jöns, head of the ‘Hybrid Photonics Quantum Devices’ research group and a member of the board of the Institute for Photonic Quantum Systems (PhoQS) at Paderborn University.

For background: entangled systems made up of multiple quantum particles offer crucial benefits for quantum communication. Rather than a single state resulting from the conditions of one photon, this produces a whole system made up of multiple states. Systems like these are used in communication, data security or quantum computing. Entanglement means that specific properties of photons are coupled together. A state represents a piece of information being processed. ‘Previously, these photons came from one and the same source, i.e. the same emitter. Although there has been significant process made in recent years, using distinct quantum emitters to implement a quantum relay between independent parties had previously remained out of reach’, Professor Jöns noted.

Some ten years ago, Professor Jöns and Professor Trotta developed a roadmap for how quantum dots could 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’, Professor Jöns said, adding: ‘The combination of excellent materials science, nanofabrication and optical quantum technology was the key to our success.’

Technological excellence across numerous research locations

This success is based on a Europe-wide research collaboration: the quantum dots were developed with the utmost precision at Johannes Kepler University Linz. Nanofabrication of the resonators was completed by partners at the University of Würzburg. Scientists at the Sapienza University of Rome conducted the quantum teleportation experiments, including a 270m free-space optical link connecting two university buildings. The protocol exploits GPS-assisted synchronization, ultra-fast single photon detectors as well as stabilization systems that compensate for atmospheric turbulence. The achieved teleportation state fidelity (i.e. the quality in which quantum states are preserved during teleportation) reaches up to 82 ± 1%, above the classical limit by more than 10 standard deviations.

Looking ahead: first quantum relay with two deterministic sources

This success paves the way for the next major step: demonstrating ‘entanglement swapping’ between two quantum dots. This would be the first quantum relay with two deterministic sources of entangled photon pairs. By way of explanation, deterministic quantum sources produce relatively reliable single photons, almost at the touch of a button. Thus far, this has involved major challenges.

Simultaneous progress

Independently, and virtually at the same time, a research team from Stuttgart and Saarbrücken achieved a similar result using frequency conversion. Together, the two projects represent a vital milestone for European quantum research.