Researchers at the Department of Energy’s Oak Ridge National Laboratory have demonstrated that advanced quantum-based cybersecurity can be realized in a deployed fiber link.

Their results, published in Physical Review Applied, validate an earlier proof-of-principle laboratory experiment by ORNL scientists in 2015.

The team transmitted a quantum signal for quantum key distribution –– a secure approach to sharing a secret key –– using a true local oscillator. A local oscillator quells the effects of noise scattered from other data transmitted in the same fiber-optic network, and the work demonstrated coexistence between the quantum and conventional data signals.

The signal traveled across ORNL’s fiber-optic network encoded in continuous variables that described the properties of light particles, or photons, in amplitude and phase. Using continuous variables of photons for encoding allows an almost infinite number of settings for distributing randomness that can be used for cybersecurity and enables compatibility with existing classical communications systems.

The ORNL team’s experiment not only broke new ground in information security but leveraged existing fiber-optic infrastructure, which would enable cheaper, easier adoption. 

The experiment resolved major roadblocks to implementing quantum key distribution while enhancing security, said Nicholas Peters, head of ORNL’s Quantum Information Science Section and the study’s principal investigator. 

“Quantum key distribution is a cryptographic protocol where two parties can generate a secure key that only they know,” Peters said. “In this experiment, this is done by using lasers to generate weak optical pulses between two points, usually referred to as Alice and Bob.”