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‘Photon Loop’ Sidesteps Defects in Delay Devices
Aug 2011
GAITHERSBURG, Md., Aug. 25, 2011 — The dawn of optical fibers a few decades ago made it possible for independent phone conversations to travel long distances across town and even across the ocean along a single glass cable with little interference. So why then, years later, is it so difficult to pass information-rich photons just a few nanometers through a computer circuit?

According to researchers at the Joint Quantum Institute (JQI) of the National Institute of Standards and Technology (NIST), the University of Maryland and Harvard University, defects in the materials that chips are made from deflect photons and distort the signal.

Artist's rendering of the proposed JQI fault-tolerant photon delay device for a future photon-based microchip. The devices ordinarily have a single row of resonators; using multiple rows provides alternative pathways so the photons can travel around any physical defects. (Image: JQI)

These defects are particularly problematic when they occur in photon delay devices, which slow the photons down to store them briefly until the chip needs the information they contain. Delay devices are usually constructed from a single row of tiny resonators, so a defect among them can ruin the information in the photon stream. The research team observed, however, that using multiple rows of resonators would build alternate pathways into the delay devices, allowing the photons to find their way around defects easily.

Because delay devices are considered a vital part of computer circuits, the alternate-pathway technique may help overcome obstacles to the development of photon-based chips, which are still a dream of computer manufacturers. The researchers said that this effort could also offer a way to explore a particularly strange effect of the quantum world known as the quantum Hall effect, in which electrons can interfere with themselves as they travel in a magnetic field.

"The photons in these devices exhibit the same type of interference as electrons subjected to the quantum Hall effect," said JQI’s Mohammad Hafezi. "We hope these devices will allow us to sidestep some of the problems with observing the physics directly, instead allowing us to explore them by analogy."

For more information, visit:

Americascomputer circuitsdeflect photonsfiber opticsHarvard Universityinformation-rich photonsJoint Quantum InstituteJQIlight sourcesMarylandMassachusettsMohammad HafezinanoNational Institute of Standards and TechnologyNISToptical fibersopticsphoton delay devicesphoton loopphoton streamphoton-based chipsquantum Hall effectResearch & TechnologyUniversity of Maryland

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