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Long distance, top secret messages

Critical component of quantum communication device may enable cryptography

When the military needs to send the key to encrypted data across the world, it can't necessarily rely on today's communication lines, where the message could be covertly intercepted.

But physicists at the Georgia Institute of Technology in Atlanta are developing a new, more secure way to send such information across far distances, using existing cables and the laws of quantum mechanics.

Alex Kuzmich and colleagues have built a critical component of a quantum repeater, a device that allows quantum communications -- such as the encryption keys used to encode data transmitted over traditional lines -- to be relayed over larger distances. They will describe this device at the Optical Society's (OSA) 94th annual meeting, Frontiers in Optics (FiO) 2010, at the Rochester Riverside Convention Center in Rochester, N.Y., from Oct. 24-28.

Quantum cryptography is an emerging technology currently used by both military and financial organizations to send information as entangled particles of light. In theory, anyone who tries to tap into this information changes it in a way that reveals their presence.

A quantum repeater is similar to a transformer on a traditional power line. 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.

Previously, the longest distance over which an encrypted key could be sent was approximately 100 kilometers. The new technology developed by the Georgia Tech team increases 30-fold the amount of time the memory can hold information, which means that series of these devices -- arrayed like Christmas lights on a string -- could reach distances in excess of 1,000 kilometers.

"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.

The talk, "Quantum Correlations Between Telecom Light and Memory" is at 9:15 a.m. on Wednesday, Oct. 27.

About the Meeting

Frontiers in Optics 2010 is OSA's 94th Annual Meeting and is being held together with Laser Science XXVI, the annual meeting of the American Physical Society (APS) Division of Laser Science (DLS). The two meetings unite the OSA and APS communities for five days of quality, cutting-edge presentations, fascinating invited speakers and a variety of special events spanning a broad range of topics in physics, biology and chemistry. FiO 2010 will also offer a number of Short Courses designed to increase participants' knowledge of a specific subject while offering the experience of insightful teachers. An exhibit floor featuring leading optics companies will further enhance the meeting.

Useful Links:

Meeting home page
Conference program
Searchable abstracts

EDITOR'S NOTE: A Press Room for credentialed press and analysts will be located in Aqueduct AB of the Rochester Riverside Convention Center, Sunday through Thursday. Those interested in obtaining a press badge for FiO should contact OSA's Lyndsay Basista at +1 202.416.1930 or

About OSA

Uniting more than 106,000 professionals from 134 countries, the Optical Society (OSA) brings together the global optics community through its programs and initiatives. Since 1916 OSA has worked to advance the common interests of the field, providing educational resources to the scientists, engineers and business leaders who work in the field by promoting the science of light and the advanced technologies made possible by optics and photonics. OSA publications, events, technical groups and programs foster optics knowledge and scientific collaboration among all those with an interest in optics and photonics.

Lyndsay Basista | EurekAlert!
Further information:

Further reports about: OSA Optic laser system optical data quantum repeater

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