Researchers at Toshiba Europe have used quantum key distribution (QKD) cryptography to send messages a record 254km using a traditional fibre optic cable network. It’s the first time scientists have achieved a coherent quantum communication using existing telecomms infrastructure.

The breakthrough marks a step closer to ultra-secure quantum encryption, which could fend off hacks from even the most advanced classical and quantum computers of the future.  

QKD is a form of communication that uses the principles of quantum mechanics to securely share encryption keys between two parties. It transmits information in the form of light. These photons carry qubits, the basic units of quantum information. 

Crucially, it is impossible to “listen in” on a quantum message without disturbing the quantum states. It would instantly alert both parties to eavesdropping. This makes the technology “untappable.”

Quantum communication typically relies on expensive lasers and cryogenic cooling equipment. The researchers, however, were able to send quantum messages via fibre optic cable, potentially bringing the technology closer to practical applications in telecoms.   

In the test, conducted last year, the team established a quantum communications network spanning 254km of existing commercial optical fibre in Germany. The network connected telecom data centres in Frankfurt and Kehl via a relay node in Kirchfeld. 

The system managed to send quantum messages twice the distance of the record set in previous QKD research, without cryogenic cooling. While the data transmission was slow — 110 bits per second — it still represents an important stepping stone. The findings were published in Nature this week.

“This work opens the door to practical quantum networks without needing exotic hardware,” Mirko Pittaluga, one of the paper’s lead authors, told IEEE Spectrum. “It lowers the entry barrier for industry adoption.” 

Today, confidential information is transmitted online using encryption keys that would take classical computers an impractically long time to break. Quantum computers, however, are a different story. 

By exploiting quantum phenomena like superposition and entanglement, quantum computers can process many more possibilities at once. As these machines get more powerful, they could potentially hack the most secure classical encryptions in a matter of minutes. They could also break all internet encryption on what is known as Q-Day. No wonder global governments are scrambling to develop their own quantum cryptography infrastructure. 

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