And now light signals can be stored as patterns in a room-temperature vapor of atoms. Scientists at the Joint Quantum Institute (*) have stored not one but two letters of the alphabet in a tiny cell filled with rubidium (Rb) atoms which are tailored to absorb and later re-emit messages on demand. This is the first time two images have simultaneously been reliably stored in a non-solid medium and then played back.
Having stored one image (the letter N), the JQI physicists then stored a second image, the letter T, before reading both letters back in quick succession. The two "frames" of this movie, about a microsecond apart, were played back successfully every time, although typically only about 8 percent of the original light was redeemed, a percentage that will improve with practice. According to Paul Lett, one of the great challenges in storing images this way is to keep the atoms embodying the image from diffusing away. The longer the storage time (measured so far to be about 20 microseconds) the more diffusion occurs. The result is a fuzzy image.
Paul Lett plans to link up these new developments in storing images with his previous work on squeezed light. "Squeezing" light is one way to partially circumvent the Heisenberg uncertainty principle governing the ultimate measurement limitations. By allowing a poorer knowledge of a stream of light---say the timing of the light, its phase---one gain a sharper knowledge of a separate variable---in this case the light's amplitude. This increased capability, at le ast for the one variable, allows higher precision in certain quantum measurements.
"The big thing here," said Lett, "is that this allows us to do images and do pulses (instead of individual photons) and it can be matched (hopefully) to our squeezed light source, so that we can soon try to store "quantum images" and make essentially a random access memory for continuous variable quantum information. The thing that really attracted us to this method---aside from its being pretty well-matched to our source of squeezed light---is that the ANU group was able to get 87% recovery efficiency from it - which is, I think, the best anyone has seen in any optical system, so it holds great promise for a quantum memory."
The lead author of the new Optics Express article, Quentin Glorieux, feels that the JQI image storage method represents a potentially important addition to the establishment of quantum networks, equipment which exploits quantum effects for computing, communications, and metrology. "It is very exciting because images and movies are familiar to everyone. We want to go to the quantum level. If we manage to store quantum information embedded in an image or maybe in multiple images, that could really hasten the advent of a quantum network/internet."
(*)The Joint Quantum Institute is operated jointly by the National Institute of Standards and Technology in Gaithersburg, MD and the University of Maryland in College Park.
(**) "Temporally multiplexed storage of images in a gradient echo memory," by Quentin Glorieux, Jeremy B. Clark, Alberto M. Marino, Zhifan Zhou, Paul D. Lett, Optics Express Vol. 20, Iss. 11, pp. 12350� (2012). http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-20-11-12350
Paul Lett, firstname.lastname@example.org, 301-975-6559 Quentin.email@example.com
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