An international research team including scientists from the University of Paderborn has reached an important milestone on the road to a quantum internet. For the first time, they were able to teleport the polarization state of a single photon from one quantum dot to another physically separated quantum dot. Simply put, this means that the properties of one photon have been transferred to another photon through quantum teleportation.
This result is an important step for future quantum communication networks. In the experiment, the researchers connected the system using a 270-meter free-space optical link. The research results were published in a magazine nature communications.
A decade of collaboration comes to fruition
At the University of Paderborn, doctoral students and postdoctoral researchers worked on optical measurements, data analysis, and evaluation for about 10 years. During this time, Professor Klaus Jons’ group worked closely with a team led by Professor Rinaldo Trotta from the Sapienza University of Rome.
“This experiment impressively shows that quantum light sources based on semiconductor quantum dots could serve as a key technology for future quantum communication networks. The successful quantum teleportation between two independent quantum emitters represents an important step towards the practical application of scalable quantum relays and thus quantum internet,” explained Professor Jons, head of the “Hybrid Photonics Quantum Devices” research group and director of the institute. Photonic Quantum Systems (PhoQS) at the University of Paderborn.
Why entanglement is important for quantum communication
Entangled systems composed of multiple quantum particles offer significant advantages in communication technology. Rather than relying on a single state determined by a single photon, these systems create interconnected states across multiple particles. This approach is essential for secure communications, data processing, and quantum computing applications.
Entanglement connects certain properties of photons and allows them to share information. A state represents a unit of information to be processed. “Previously, these photons came from a single, same source, i.e. from the same emitter. In recent years, important processes have been carried out, but the use of separate quantum emitters to implement quantum relay between independent parties was previously out of reach,” Professor Jons pointed out.
Long-term strategy and advanced technology
About 10 years ago, Professors Jons and Trotta outlined plans to use quantum dots as a source of entangled photon pairs in communications and teleportation systems. Their recent success confirms that this long-term approach is paying off.
“This result shows that our long-term strategic plan is paying off,” Professor Jons said, adding, “The combination of excellent materials science, nanofabrication and photon technology was the key to our success.”
Collaboration across Europe delivers accurate results
This breakthrough relied on contributions from several research centers across Europe. The quantum dots were precisely designed at the Johannes Kepler University in Linz, and the nanofabrication of the cavity was carried out by partners at the University of Würzburg. The teleportation experiment itself took place at Sapienza University in Rome, where scientists connected two buildings using a 270-meter free-space optical link.
The system used GPS-assisted synchronization, ultrafast single-photon detectors, and stabilization methods to counter atmospheric turbulence. The achieved teleportation state fidelity (i.e., the quality with which the quantum state is preserved during teleportation) reaches up to 82 ± 1%, exceeding the classical limit by more than 10 standard deviations.
Next step: Building a quantum relay
This achievement opens the door to the next goal of demonstrating “entanglement exchange” between two quantum dots. Achieving this creates the first quantum relay using two deterministic sources of entangled photon pairs. Deterministic light sources can reliably produce single photons almost on demand, but their development has been a major challenge.
Concurrently strengthening quantum research
At about the same time, another research team in Stuttgart and Saarbrücken reported similar results using frequency translation. Taken together, these results represent an important milestone for quantum research in Europe and bring the vision of a functional quantum internet closer to reality.
