German researchers have achieved a milestone by transmitting quantum communications across 150 miles of standard commercial fiber-optic lines—linking Frankfurt, Kehl, and Kirchfeld—without overhauling existing telecom infrastructure.
This proof-of-principle used off-the-shelf components to send quantum keys over 254 km of deployed fiber, setting a new record for coherent quantum key distribution in real-world conditions. The breakthrough proves that nationwide quantum-secure networks can be built at a fraction of the cost previously imagined.
A standout feature is the team’s use of avalanche photodiodes operating near room temperature instead of bulky, cryogenically cooled detectors. This innovation slashes complexity and energy demands, making quantum cryptography practical for banks, hospitals, and critical infrastructure.
They also implemented the Twin Field Quantum Key Distribution protocol, achieving secure key rates of around 110 bits per second over the full span, and demonstrated measurement-device-independent security to guard against side-channel attacks.
The key benefit is virtually unhackable data links: quantum mechanics ensures that any eavesdropping attempt disrupts the quantum states and is immediately detected, offering a level of security beyond today’s encryption standards.
However, integrating quantum signals into conventional networks presents new challenges—classical traffic and fiber imperfections can introduce noise—so robust error correction and active stabilization are essential. Despite these hurdles, this work paves the way for metropolitan-scale quantum networks without laying new cables, accelerating the arrival of a quantum internet.
This news matters because the looming threat of quantum computers could soon render current encryption obsolete. By demonstrating practical, cost-effective quantum key distribution over hundreds of kilometers, the German team has charted a clear path toward future-proof communications that protect sensitive data against next-generation cyberattacks
As lead researcher Mirko Pittaluga notes, this approach “opens the door to many exciting quantum technologies transitioning out of the lab and into practical networks”.
Key Quote
“This work opens the door to many exciting quantum technologies transitioning out of the lab and into practical networks.”
— Robert Woodward, Toshiba Europe
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