Scientists at Toshiba and Cambridge University have perfected a technique that offers a less expensive way to ensure the security of the high-speed fiber optic cables that are the backbone of the modern Internet.

The research, which will be published Tuesday in the science journal Physical Review X, describes a technique for making infinitesimally short time measurements needed to capture pulses of quantum light hidden in streams of billions of photons transmitted each second in data networks. Scientists used an advanced photodetector to extract weak photons from the torrents of light pulses carried by fiber optic cables, making it possible to safely distribute secret keys necessary to scramble data over distances up to 56 miles.

Such data scrambling systems will most likely be used first for government communications systems for national security. But they will also be valuable for protecting financial data and ultimately all information transmitted over the Internet.

The approach is based on quantum physics, which offers the ability to exchange information in a way that the act of eavesdropping on the communication would be immediately apparent. The achievement requires the ability to reliably measure a remarkably small window of time to capture a pulse of light, in this case lasting just 50 picoseconds — the time it takes light to travel 15 millimeters.