A quantum internet is no longer just theory after scientists successfully teleported the polarisation state of a photon between two completely different quantum dots located in separate buildings.
The experiment, detailed in Nature Communications, involved transmitting quantum information across a 270-metre free-space optical link in Rome, marking the first time such a feat has been achieved using distinct quantum emitters.
Researchers from Paderborn University and Sapienza University of Rome achieved a teleportation state fidelity of 82 per cent — exceeding the classical limit by more than 10 standard deviations.
This fidelity score is critical, as it proves that the quantum information was preserved accurately during the transfer between the physically separated locations.
“The experiment impressively demonstrates that quantum light sources based on semiconductor quantum dots could serve as a key technology for future quantum communication networks,” said Professor Klaus Jöns, head of the Hybrid Photonics Quantum Devices research group at Paderborn University.
“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.”
Synchronising separate systems
Historically, quantum teleportation experiments have relied on photons generated from a single source to ensure compatibility.
Using distinct quantum emitters to create a relay between independent parties had previously remained elusive due to the extreme difficulty of synchronising separate systems.
The team overcame this hurdle by employing GPS-assisted synchronisation and stabilisation systems to compensate for atmospheric turbulence over the outdoor optical link.
The success paves the way for “entanglement swapping” between two quantum dots, a process necessary to build the first quantum relays using deterministic sources.
In a parallel development, a research team from Stuttgart and Saarbrücken achieved a similar result using frequency conversion at virtually the same time, marking a dual milestone for European quantum research.
