News Feature: Code wars

In October 2014, an Antares rocket blasted off from a NASA launch pad on one of Virginia’s barrier islands, and exploded seconds later. In addition to about 5,000 pounds of food and equipment destined for the International Space Station, the doomed rocket was carrying 26 miniature satellites called CubeSats, one of which housed physicist Alexander Ling’s experiment. “We thought, ‘oh, that’s it, we’re not going to see our experiment again,’” recalls Ling, of the Centre for Quantum Technologies in Singapore. He was mistaken. Days later, Ling got a phone call. His experiment had washed up on a nearby beach. The CubeSat’s metal casing had been crushed—“a bit,” says Ling, but the experiment inside had not only survived but was still working. The nature of the experiment made this even more astonishing: Their device used crystals and lasers to generate particles of light, or photons, in delicate, easily destroyed quantum states. Neither the turbulence of the launch nor the shock of the explosion had knocked the device out of alignment. Ling was ecstatic. Although the mission had failed, his experiment had endured. He and other quantum cryptography researchers hope that expectations about the technology’s potential hold up just as well. Ling wants to help build a global quantum Internet in which computers would communicate securely using the quantum mechanical properties of particles of light. Such an effort would require both networks on the ground, built over existing fiber-optic cables, and in space, using satellites capable of exchanging photons in fragile quantum states, like those at the heart of Ling’s design. One of the most tantalizing implications of such a quantum network is its apparent impregnable security. That’s important because vulnerabilities lurk in even the most robust encryption methods that protect information transmitted across existing communication networks. Ultrafast quantum computers of the future, which will exploit quantum states of particles to perform multiple calculations at once, could easily break today’s strongest codes. Many physicists say the only way to thwart quantum computers is to fight fire with fire, using cryptography that itself relies on quantum mechanics. “For quantum cryptography, security is the whole selling point,” says VadimMakarov, an applied physicist at the Institute for Quantum Computing at the University of Waterloo, in Canada.