Eugene, OR--University of Oregon (UO) scientists have invented a method to change the color of single photons in a fiber-optic cable. The laser-tweaked feat could be a quantum step forward for transferring and receiving high volumes of secured data for future generations of the Internet. The proof-of-concept experiment from UP physicist Michael G. Raymer was reported in the August 27 issue of Physical Review Letters, and has important implications for quantum-computing applications.
"There is a need for more bandwidth, or data rate, in fiber optic networks," says Raymer. "In today's fiber optic lines one frequency of light may carry a phone conversation, while others may carry TV channels or emails, all traveling in separate channels across the Internet. At the level of single photons, we would like to send data in different channels--colors or wavelengths--at the same time. Quantum memories based on electrons emit and absorb visible light--for example, red," he said. "But the optical fibers we want to use--such as those in the ground now--are optimized to transmit infrared, not visible light."
In experiments led by Raymer's doctoral student Hayden J. McGuinness, researchers used two lasers to create an intense burst of dual-color light, which when focused into the same optical fiber carrying a single photon of a distinct color causes that photon to change to a new color. This occurs through a process known as Bragg scattering, whereby a small amount of energy is exchanged between the laser light and the single photon, causing its color to change. This process, demonstrated in the UO’s Oregon Center for Optics, is called quantum frequency translation. It allows devices that talk to one another using a given color of light to communicate with devices that use a different color.
"Other researchers have done this frequency translation using certain types of crystals," Raymer said. "Using optical fibers instead creates the translated photons already having the proper shape that allows them to be transmitted in a communication fiber. Another big advantage of our technique is that it allows us to change the frequency of a single photon by any chosen amount. The objective is to convert a single photon from the color that a common quantum memory will deal with into an infrared photon that communication fibers can transmit. At the other end, it has to be converted back into the original color to go into the receiving memory to be read properly."
SOURCE: University of Oregon; http://uonews.uoregon.edu/archive/news-release/2010/9/physicists-break-color-barrier-sending-receiving-photons
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