The data is encoded with an encrypted key but one important limitation is range. The longest distance over which an encrypted key can be sent is approximately 100 kilometers but new technology developed by researchers increases 30-fold the amount of time the memory can hold information, which means that a series of quantum repeaters, arrayed like Christmas lights on a string, could reach distances in excess of 1,000 kilometers.
A quantum repeater is similar to a transformer on a traditional power line but instead of converting electricity, it regenerates a communication signal to prevent it from degrading over distance. It contains two banks of memory, one to receive an entangled message and a second line to copy it. Alex Kuzmich and colleagues from the Georgia Institute of Technology have built a critical component of the quantum repeater, necessary to allow quantum communications such as the encryption keys to be relayed over larger distances - and using traditional cables.
"This is another significant step toward improving quantum information systems based on neutral atoms. For quantum repeaters, most of the basic steps have now been made, but achieving the final benchmarks required for an operating system will require intensive optical engineering efforts," says Kuzmich.
Their device also converts the photons used in quantum devices from an infrared wavelength of 795 nm to a wavelength of 1,367 nm. This wavelength is used in traditional telecommunications lines, so the new device could someday plug into existing fiber optic cables.
"In order to preserve the quantum entanglement, we perform conversion at very high efficiency and with low noise," says Alexander Radnaev, who also works on this project at Georgia Tech.
They will describe this device this week at the Optical Society's (OSA) 94th annual meeting, Frontiers in Optics (FiO) 2010, at the Rochester Riverside Convention Center in Rochester, N.Y., Oct. 24-28.
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