Researchers at the University of Stuttgart have achieved a major milestone toward realizing a functional quantum internet by demonstrating quantum teleportation between photons emitted from two different quantum dots. This accomplishment—published in Nature Communications—overcomes a central challenge in building quantum repeaters, devices essential for extending quantum communication beyond the roughly 50-kilometer limit imposed by fiber-optic signal loss. Led by Prof. Peter Michler, the team used nanometer-scale semiconductor quantum dots to generate highly controlled photons and transfer quantum information while preserving its unknown state. Their success in producing and interfering indistinguishable photons from separate sources marks a pivotal advance toward scalable quantum-network nodes and long-distance, secure quantum communication.

Figure 1. Advancing Quantum Repeaters for the Quantum Internet

A key obstacle to creating a quantum internet is the short transmission range of photons in optical fibers, which lose signal strength after about 50 kilometers. Because quantum information cannot be amplified, long-distance communication requires quantum repeaters that teleport information between photons while keeping the underlying quantum state unknown. Building on earlier work that showed entanglement can survive 36 kilometers of fiber within Stuttgart, the research team has now demonstrated successful teleportation over a 10-meter link. Figure 1 shows Advancing Quantum Repeaters for the Quantum Internet.

Their current teleportation success rate exceeds 70%, though it is limited by fluctuations in the quantum dots, which introduce small variations between photons. Improving semiconductor fabrication is a major focus to reduce these inconsistencies. This effort is part of the large “Quantenrepeater.Net (QR.N)” consortium of 42 partners, which aims to test next-generation quantum repeater technology in real fiber networks and extend the progress achieved in the earlier “Quantenrepeater.Link (QR.X)” program.

Quantum Repeaters and Quantum State Teleportation

Researchers at the University of Stuttgart have made a significant advance in quantum repeater technology by teleporting quantum information between photons emitted by different quantum dots. In their experiment, the polarization state of one photon was transferred to another using entangled photon pairs and quantum frequency converters that corrected mismatches between the photons. Since quantum information cannot be amplified like classical signals in fiber-optic networks, this capability is essential for renewing quantum states over long distances and represents a key step toward building scalable quantum communication systems.

The experiment depended on producing nearly identical photons from separate quantum dots—a major technical hurdle. To achieve this, the team engineered semiconductor islands with fixed energy levels that emit single photons with well-defined properties. Although the dots in this experiment were only 10 meters apart, earlier work had already shown that entanglement could survive a 36-kilometer fiber transmission through Stuttgart. The current quantum teleportation success rate is just above 70%, and researchers are working to improve it through more precise semiconductor fabrication.

Quantum repeaters are vital components for a future quantum internet, enabling long-distance communication by countering signal degradation in optical fibers without relying on classical amplification. This work is part of the large “Quantenrepeater.Net (QR.N)” consortium of 42 partners and builds on the earlier “QR.X” initiative. The overarching goal is to develop a secure, scalable quantum communication network protected by the fundamental principles of quantum mechanics.

Advancing Quantum Teleportation Systems

Researchers at the University of Stuttgart have achieved a major breakthrough in quantum repeater development by teleporting quantum information between photons produced by different quantum dots for the first time. Using nanometer-scale semiconductor islands to generate highly controlled photons, the team successfully transferred a photon’s polarization state through entanglement and quantum frequency conversion.

This milestone helps overcome one of quantum communication’s biggest challenges: severe signal loss in optical fibers, which cannot be countered with conventional amplification because quantum states can’t be copied. Instead, quantum repeaters use teleportation to faithfully transfer information from one photon to another, effectively renewing the signal. In this experiment, quantum dots 10 meters apart were linked, building on earlier work that preserved entanglement across 36 kilometers of fiber within Stuttgart.

Teleportation success currently exceeds 70%, with ongoing efforts to enhance it through improved semiconductor fabrication [1]. By reducing variations in quantum dots, researchers aim to produce more identical photons and increase efficiency. Supported by the Federal Ministry of Research, Technology and Space under the “Quantenrepeater.Net (QR.N)” project, this work represents a key step toward establishing a secure, quantum-enabled internet.

References:

1. https://quantumzeitgeist.com/quantum-repeaters-quantum-internet/

Cite this article:

Janani R (2025), Quantum Repeaters: A Major Leap Toward the Quantum Internet, AnaTechMaz, pp. 257