Another step toward quantum computers: using photons for memory

April 3, 2013

Photograph of one half of two aluminum waveguide cavities coupled to a qubit. Right, a magnified view of the indicated area of the photograph, showing a detail of the qubit, fabricated on a sapphire substrate. (Credit: Gerhard Kirchmair et al./Nature)

Scientists at Yale University have found a way to use microwave photons to store quantum information.

Photons can carry and hold quantum information for a long time, because they interact weakly with the media they typically travel through — coaxial cables, wires, or air, for example.

The weakness of these interactions prevents the photons from being absorbed by the medium and preserves the quantum information, once it’s been encoded.

In a Nature paper, the researchers report creating an artificial medium in which photons repel photons, allowing for efficient, non-destructive encoding and manipulation of quantum information.

“Our experiment has shown that we can create a medium that on the one hand enables us to manipulate the photon state, and on the other hand does not absorb the photons, which would destroy the quantum information stored in them,” said Gerhard Kirchmair, a postdoctoral researcher at Yale and the paper’s lead author.

“This creates a source for novel quantum states without the need for complicated control techniques and could simplify certain quantum computation algorithms. In the long run it could be used as one of the many resources required to build a quantum computer.”

The medium consists of a superconducting qubit coupled to a microwave cavity resonator.

“The tricky bit for future experiments will be to switch on and off this effect at will, so that it only happens if we want it to happen,” said Kirchmair. “We already have experiments on the way that show that we can do that.”

The National Science Foundation, the U.S. Army, the French Angence Nationale de la Recherche, the Swiss NSF, and the British Engineering and Physical Sciences Research Council all supported the research.