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Glass Micro-Rings Show Their Worth as Quantum Test Bed

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COURTESY OF K. J. VAHALA
A mass-producible, toadstool-shaped piece of glass may be just the thing for developing future technologies that harness quantum weirdness. Researchers have managed to control the flow of light through such toadstools by touching atoms to them, demonstrating that the devices could serve as nodes of a quantum network in which information is traded between atoms and light.

Schemes based on quantum strangeness promise the eventual development of extremely powerful computers or encryption systems, once researchers figure out the best way to manipulate the fussy quantum states of matter and light. One approach is to construct a network that stores information in the long-lived states of atoms, which would serve as the nodes in the network, and manipulate that information by playing light between the nodes. The challenge for researchers, then, is to get atoms and light to talk to each other in a way that easily scales up to hundreds or thousands of nodes. A traditional method for linking an atom to a photon is to bounce light between two mirrored walls and drop an atom inside, but these microcavities are hard to improve on and to mass-produce.

Kerry Vahala and Jeff Kimble of the California Institute of Technology, along with their colleagues, opted instead to use a 40-micrometer-wide ring of silicon dioxide (glass) on a pedestal of the same material, which they etched on a silicon microchip using standard lithographic techniques. The group tapered an optical fiber to make it narrow in the middle and positioned the constriction next to the ring. When light of a certain frequency was shined through the fiber it leaked from the constriction into the ring, where it circled, resonating like light in a cavity. The researchers then dropped a cloud of ultracold cesium atoms onto the structure. A cesium atom passing nearby should have interacted with the ring's electric field, in this case changing its resonant frequencies so that the light was no longer able to travel through it, explains team member Barak Dayan. Instead, the light should have continued down the fiber, and this is what the group observed, according to the October 12 Nature. The next step will be to precisely position an atom near the ring, Dayan says.

The scalability of the ring structure should make it a useful complement to other quantum information test beds, says experimental physicist Christopher Monroe of the University of Michigan. "You could easily have 10,000 of them all manufactured in exactly the same way," he says. "That's exactly what quantum information is all about--being scalable."

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