Unhackable quantum messages travel 158 miles without cryogenics for first time

Yahoo

27-04-2025

Cybersecurity experts often warn that a moment known as Q-Day is nearby—a day when quantum computers will become powerful enough to break all the encryption methods we currently rely on to keep our information secure.
Q-Day is not some imaginary situation but a real-world threat that could disrupt the internet and global digital infrastructure. Various government agencies and private organizations are already taking measures to withstand attacks from powerful quantum computers.
These measures include the development of new encryption methods designed to resist quantum attacks, as well as exploring techniques like quantum key distribution (QKD) to secure communications at a fundamental level.
Recently, a team of researchers from Toshiba Europe successfully transmitted messages over a 254-kilometer (~158 miles) stretch of existing fiber-optic infrastructure using QKD cryptography. Such a feat has been achieved for the first time.
Moreover, unlike typical quantum communication setups, this method didn't require a cryogenic system or an advanced, high-tech laser. 'This work opens the door to practical quantum networks without needing exotic hardware,' Mirko Pittaluga, one of the researchers, said in an interview with IEEE Spectrum.
To achieve long-distance quantum messaging, the researchers set up a network across 254 kilometers of commercial optical fiber in Germany, linking data centers in Frankfurt and Kehl, with a central relay node in Kirchfeld.
In most quantum communication systems, keeping the light waves precisely synchronized over long distances requires stable lasers. However, instead of using expensive ultrastable lasers, the researchers used a simpler method.
The central node in Kirchfeld sent laser beams to both Frankfurt and Kehl, providing a common reference. This allowed the researchers to synchronize the light phases effectively without needing highly specialized equipment.
For detecting weak quantum signals, traditional systems usually rely on superconducting nanowire detectors, which are very sensitive but require costly and bulky cryogenic cooling units. The team instead used avalanche photodiodes, semiconductor devices capable of detecting single photons.
Avalanche photodiodes are much cheaper and operate at room temperature, but they are less efficient and more prone to false detections. To overcome these limitations, the researchers sent a reference laser pulse along with the quantum data and installed two sets of avalanche photodiodes at each receiving station.
One set dealt with quantum communication, while the other set monitored the reference signals. This setup helped correct errors caused by vibrations, temperature changes, and other disturbances in the optical fiber cables.
All these clever techniques allowed the researchers to successfully demonstrate QKD over a 254 km optical fiber network, which is double the distance achieved during previous experiments.
Although, for now, the system is capable of transmitting data at only 110 bits per second, it still marks a significant breakthrough for something that was once thought to be impossible.
The researchers suggest that boosting the data rate beyond 110 bits per second is the next big goal. One simple way to do this is by making the system encode faster.
For instance, currently, it runs at 500 megahertz. Using existing technology, it could be scaled up to a few gigahertz. This alone could boost the data transmission rate by nearly ten times.
Moreover, they are also working on building quantum repeaters, special devices that could prevent signal losses and further increase the distance and speed of quantum messaging.
Hopefully, further research will help scientists realize all these goals soon, helping to build a more secure digital world before Q-Day arrives.
The study is published in the journal Nature.