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Artificial atoms interact across a distance

Researchers created a system of two artificial atoms which maintained quantum interactions by sharing photons across a distance. The result could help scientists gain insight into basic physics, and could lead to improvements in quantum communication and quantum computers.

The work by was done by an international team of researchers included two CIFAR Fellows, and was reported in the journal Science last week.

“This result could be very useful in quantum computation,” says Alexandre Blais, a CIFAR Fellow in the program Quantum Information Science and a researcher at Université de Sherbrooke. “But we’ve also demonstrated that these artificial atoms are better than natural atoms for a wide range of experiments in quantum mechanics.”

One way that atoms interact with each other is by exchanging photons – either real photons or “virtual” photons, which blink spontaneously in and out of existence in an instant. But these interactions are hard to observe between real atoms, in part because a photon can be emitted in any direction.

To solve the problem, Blais and CIFAR Senior Fellow Barry Sanders of the University of Calgary teamed up with experimentalists at ETH Zurich. The Zurich researchers fabricated two transmons – tiny pieces of superconductor that in some ways behave like natural atoms. Then they connected these artificial atoms along a channel etched into a surface that served as a waveguide. When one of the artificial atoms emitted a photon, the photon was forced to travel along the channel, making it much more likely to interact with the other artificial atom.

The researchers showed that the artificial atoms linked by the waveguide worked as a single system, exchanging photons and virtual photons. In fact, the two artificial atoms could be seen as a single molecule, weakly linked by the quantum interaction of exchanging photons. The interaction continued when the artificial atoms were separated by as much as two centimeters – a huge distance in quantum terms – and is expected to persist at even greater distances.

“I think what we’ve shown here is going to be critical for future applications,” says Sanders. The finding could be useful for protecting quantum information from errors caused by environmental noise, or for sending information from one location to another. Sanders says that researchers are just coming to grips with the potential applications.

Blais and Sanders credited CIFAR for helping them collaborate together. The two men met at a CIFAR program meeting in Halifax in 2005, and have been working together ever since. “I would not even have met Barry without CIFAR,” Blais says.

CIFAR’s QIS program unites computer scientists and physicists in an effort to harness quantum effects to build more powerful computers. The group bridges a gap between quantum computing theory and experimental realization, and brings quantum computing closer to realistic possibility.

In addition to Sanders and Blais, authors included Arjan F. van Loo, Arkady Fedorov and Andreas Wallraff of ETH Zurich, and Kevin Lalumière, also of Sherbrooke.

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