Researchers from Paderborn University and Sapienza University of Rome have pulled off a feat that quantum physicists have been chasing for more than a decade: teleporting the quantum state of a single photon from one semiconductor quantum dot to another, with 270 metres of open air in between.
The result, published in Nature Communications and announced this week, is the first time the polarisation state of a photon has been transferred between two physically separated, independent quantum emitters. It is a critical building block for the long-promised "quantum internet" — a future network that could send information with security guarantees physics itself enforces.
A long bet that finally paid off
Quantum teleportation does not move matter. It transfers the delicate state of one quantum particle to another using a shared resource called entanglement. Until now, demonstrations between distant labs almost always relied on photons coming from a single source. Linking two truly independent emitters across hundreds of metres has been on physicists'' wish list for years.
About a decade ago, Professor Klaus Jöns at Paderborn and Professor Rinaldo Trotta at Sapienza laid out a plan to use semiconductor quantum dots — tiny crystals that can emit single photons on demand — as the workhorses of such a network. Their team has been steadily refining materials, fabrication and optics ever since.
"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."
How the experiment worked
The team built two separate quantum-dot light sources and connected them through a 270-metre free-space optical link. They then teleported the polarisation state of a photon from one source to the other, achieving a fidelity well above the classical threshold — the benchmark that proves the result is genuinely quantum, not just coincidence.
Crucially, the photons were converted to telecom wavelengths, the part of the spectrum already used by the world''s fibre-optic infrastructure. That makes the technology compatible, in principle, with existing telecommunications networks.
Why a quantum internet matters
A working quantum internet would not replace the regular internet. It would sit alongside it, offering capabilities ordinary networks cannot match: communication channels that detect any eavesdropping, secure links between quantum computers, and ultra-precise distributed sensing for everything from telescopes to navigation.
The catch is distance. Photons get absorbed and scattered as they travel, and you cannot simply amplify a quantum signal the way you do with classical light. Networks need devices called quantum repeaters, which rely on exactly the kind of teleportation between independent emitters that the Paderborn–Rome collaboration has just demonstrated.
A European-wide effort
Pulling the experiment off required teams across the continent. Quantum dots were grown at Johannes Kepler University Linz. Resonator nanofabrication came from the University of Würzburg. Optical measurements and analysis happened in Paderborn, while the integration and end-to-end teleportation protocol was led from Rome.
It is a reminder that the most ambitious quantum experiments are now logistical as much as scientific feats — choreographed across labs, cleanrooms and rooftops.
What comes next
A 270-metre link is a long way from a global network, but it is exactly the kind of intermediate step researchers needed. The next milestones include longer distances over deployed fibre, higher fidelity, and combining teleportation with quantum memories so that information can be stored as well as transferred.
For now, the message is simple: the building blocks of a quantum internet are no longer just on whiteboards. They are sitting on optical tables in Europe, working.
