Space: Final frontier for coded data?

A space experiment slightly larger than a sandwich tucked into a nanosatellite could change the way encrypted data is sent around the globe.

This is what Singaporean physicist Alexander Ling is hoping to achieve with the miniature experiment he developed with his team.

"This is the first step to extending quantum cryptography over global distances," said the 37-year-old from the Centre for Quantum Technologies (CQT) here. "It is a long way down the road, but we could even use it to protect electronic transactions for the man in the street."

Quantum cryptography, or the transmission of secrets using light particles, has been used by several European banks.

But its use is currently restricted to short distances of a few kilometres because the light particles, or photons, are mostly lost when travelling through very long optical cables. "Instead, scientists want to use satellites to beam entangled light particles from space back to Earth. Entangled light particles travel more effectively through space, which is a vacuum," said Dr Ling.

His experiment, which he hopes to launch in 2015, will see if these "entangled" light particles can be produced in space.

The usual method of keeping information secret is to encrypt it using a mathematical formula. The message is then decrypted with the use of a key. Since the rules of maths are fixed, a hacker may be able to figure out the key and break the code.

But what happens when the key changes each time someone tries to figure it out? Then rightful data owners know there has been an attempt to gain unauthorised access. This is how quantum cryptography works, based on quantum mechanics - nature's bizarre laws governing the tiniest particles of matter. Underlying this branch of science is the Uncertainty Principle, which states that any attempt to measure a quantum particle may affect its properties and leave a trace.

Another strange effect of quantum mechanics is entanglement. When something is done to one photon, its entangled partner will produce a related effect, regardless of the distance between them.

By comparing these effects, a sender and receiver of secret information will be able to generate a decoding key which is far more secure than conventional methods. "The only way a hacker can intercept your message is by measuring the state of a light particle. But this disrupts the entanglement and he will surely be found out," said Dr Ling, who worked on the experiment with fellow researchers and doctorate students.

Besides Dr Ling and his collaborators, several groups from Canada, Europe and China are also trying to make global quantum cryptography a reality.

Dr Ling, however, has reduced the standard 30kg quantum entanglement experiment to something slightly larger than a sandwich. "We wanted it to fit into a nanosatellite, so it could be launched cheaply," he said. Dr Ling is in talks with the National University of Singapore and European space conglomerate QB50 to piggyback their space missions and launch his experiment.

Scientists whom The Straits Times spoke to said the miniaturisation of the experiment is quite a feat. "If Dr Ling's experiment works, quantum cryptography could be done in a more cost-effective way in future," said Professor Christophe Salomon, a physicist from Laboratoire Kastler Brossel, who recently visited Dr Ling's laboratory.

What is quantum cryptography Quantum cryptography is the transmission of secrets using light particles.

For now, its use is restricted to short distances of a few kilometres because the light particles, or photons, are mostly lost when travelling through very long optical cables.

Several European banks are already using it.

Singaporean physicist Alexander Ling is trying to extend the reach of quantum cryptography by transmitting "entangled" light particles from space.

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