A secure key rate of two hundred and six Hertz was achieved during testing; Quantum Key Distribution using entanglement from a quantum dot source occurred for the first time. This system transmitted information across a deployed fibre optic link spanning one point five nine kilometres on campus utilising the BBM92 protocol. Secure data transmission used entangled particles emitted from a tiny semiconductor device called a quantum dot, harnessing principles of quantum mechanics for enhanced security.

By successfully sending information via existing fibre optic cables, a deployed link spanning 1.59 kilometres on campus, the team moved beyond laboratory settings towards practical applications. A new approach to Quantum Key Distribution (QKD) enabled secure data transmission. The technology creates and shares encryption keys based on the laws of physics; any attempt to intercept these keys would immediately become detectable. Achieving a key rate of two hundred and six Hertz moves QKD beyond laboratory settings toward practical applications, but can this system be scaled up for longer distances and more complex networks.

Sustained high-rate entanglement enables prolonged quantum communication

A threefold improvement, reaching a secure key rate of 206Hz, over previous solid state QKD demonstrations was sustained for nineteen hours. This duration surpasses typical experimental windows and brings continuous real-world operation for Quantum Key Distribution (QKD) closer to reality. Earlier attempts struggled with stable entanglement generation beyond short bursts or sufficient data throughput; this achievement breaks that longstanding barrier in scaling up these systems, overcoming limitations found outside controlled laboratory environments.

Nineteen hours of secure key exchange at 206Hz yielded a total secure key length reaching 14.2 Mbit using an entanglement-based QKD system developed by the University of Stuttgart team. The experiment utilised the BBM92 protocol and automated polarisation compensation over a deployed optical fibre link spanning 1.59km across the university’s Vaihingen campus.

Droplet-etched quantum dots are semiconductor nanocrystals emitting bright entangled photon pairs around 780 nanometres. These were coupled with a frequency conversion module to shift photons into the standard telecommunications wavelength range near 1515nm; this not only allowed distribution of encryption keys but also successful encryption and decryption of a colour image, demonstrating progress towards practical applications in hybrid networks.

Fibre optic transmission advances quantum networking despite unresolved security vulnerabilities

The University of Stuttgart team’s demonstration offers a promising path toward scalable quantum networks using existing fibre infrastructure, providing an advantage over free-space or bulky crystal approaches. Real-world durability remains a limitation for these systems. Specifically, full determination of system resilience against sophisticated attacks targeting imperfections within the BBM92 protocol is still needed because even theoretically secure protocols are vulnerable when implemented with imperfect devices.

An epitaxial quantum dot generating entangled photon pairs at approximately 780 nanometres bypassed limitations imposed by standard photonic components unsuitable for long distance transmission; this enabled encryption of image data and demonstrated stable operation within a solid state system employing the BBM92 protocol. Securely encrypting a colour image on campus networks demonstrates that quantum communication is moving beyond the laboratory over 1.59km fibre distances. The University of Stuttgart’s results represent vital steps towards hybrid quantum networks, establishing an interface between quantum light sources and existing fibre optic networks as they move toward practical applications for secure communication.

Using an epitaxial quantum dot to generate entangled photons, researchers successfully established a secure key distribution over a 1.59 kilometer fiber link at the University of Stuttgart campus. This demonstration achieved a stable key rate of 206Hz over nineteen hours, resulting in a total secure key length of 14.2 Mbit and enabling encryption of a colour image.

These findings show how quantum dots can be used with standard telecommunication wavelengths to connect quantum devices through existing optical infrastructure. The work represents progress towards building hybrid quantum networks that combine high-quality entanglement sources with fibre optic links for secure communication.

👉 More information
🗞 Deployed entanglement-based BBM92 quantum key distribution using frequency-converted photons emitted by a quantum dot
✍️ Michal Vyvlecka, Raphael Joos, Benjamin Breiholz, Emma Marmasse, Ilenia Neureuther, Timo Schnieber, Anna Frederike Köhler, Tim Strobel, Andreas Berg, Sebastian Kiesel, Simone Luca Portalupi and Peter Michler (University of Stuttgart); Tobias Bauer, Marlon Schäfer and Christoph Becher (Universität des Saarlandes); Nand Lal Sharma and Caspar Hopfmann (Affiliation: Institute for Integrative Nanosciences)
🧠 ArXiv: https://arxiv.org/abs/2610.37268

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