Space-borne quantum source to secure communication

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It is thought that soon, powerful quantum computers will be able to easily crack conventional mathematically encrypted codes. Entangled photons generated by a space-borne quantum source could enable hack-proof key exchange for ultra high security applications. A Fraunhofer research team has developed a quantum source robust enough for deployment in space, with the aim of launching the first European quantum satellite in some four years’ time.

The device has been put through its paces, the researchers say, enduring leaps in temperatures from -40 to +60 degrees Celsius, exposure to cold and heat in vacuum, and jarring rodeo rides on a triple-axis vibrating platform.

The quantum source is said to be capable of generating 300,000 entangled photon pairs per second when the light from a laser beam hits a non-linear crystal. These twinned light particles enable sensitive messages to be securely encrypted, the researchers claim.

The two photons’ polarization remains entangled – that is, correlated – no matter how far apart they may be. This allows two communicating parties to produce and share keys and immediately detect if a third-party attempt to intercept their communication. If an unauthorised party tampers with the message, the two photons disentangle to reveal that a hacking attempt is underway.

But why does the quantum source have to be in space? Entangled photons could also travel via fibre optic cables such as telephone lines. But this would cut the range short and impede the important process of photon entanglement. A far better option is to piggy-back the quantum source on a satellite and send it into low Earth orbit, where it can transmit the twinned light particles down to the planet from an altitude of 400km with minimal disturbance.

“The quantum source’s stability and performance presented the greatest challenges because the loss rate is still high on the way through the Earth’s atmosphere. This is why it is so important to generate as many entangled twin photons as possible to maximise the number of photons that reach the communicating parties on Earth,” explains Fraunhofer IOF project manager Dr. Oliver de Vries.

One key always requires several pairs of photons. Expounding further on this, de Vries adds, “We optimised the quantum source’s stability with a smart design, effective inorganic bonding processes, and robust materials that do not expand much in the event of temperature changes.”

The technology is already attracting a lot of attention, the researchers say, particularly from banks and government agencies that rely on secure communication. However, the infrastructure needed to share keys has yet to be established before quantum encryption can be implemented in three to five years’ time. The communicating parties would have to receive the light particles with a device like a telescope. This device, in turn, would have to be integrated into the IT structure.

Dr. de Vries has a plan in mind: “I could imagine a business model where Fraunhofer equips the satellite with a quantum source and outside partners offer the reception infrastructure and sell the keys.”

The research team’s express goal is to send the first European quantum satellite into space in around four years.