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Temporally multiplexed storage of images in a gradient echo memory

Figure 1: Gradient echo memory setup. The image to be stored, the letter N encoded by a signal laser beam and a mask, enters from the left (pink light) and enters the storage cell filled with Rb atoms. The components of this image will be absorbed by the atoms when, at locations all over the body of the cell, a part of the signal beam and parts of a separate “control” laser beam---entering from the side (shaded green) via a polarizing beam splitter (PBS) -- and (last but not least) the strength of a magnetic field (delivered by the brown coil around the cell) are just right. The stored image can later be read out and observed with a CCD camera. (Image credit: NIST)

PFC-supported scientists have stored not one but two letters of the alphabet in a tiny cell filled with rubidium 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. In effect, this is the first stored and replayed atomic movie. The new storage process was developed by Paul Lett and his JQI/PFC colleagues. The atomic storage medium is a narrow cell some 20 centimeters long, which seems pretty large for a quantum device. That’s how much room is needed to accommodate a quantum process called gradient echo memory (GEM). While many storage media try to cram as much information into as small a place as possible---whether on a magnetized strip or on a compact disk---in GEM an image is stored over the whole range of that 20-cm-long cell. The image is stored in this extended way, by being absorbed in atoms at any one particular place in the cell, depending on whether those atoms are exposed to three carefully tailored fields: the electric field of the signal light, the electric field of another “control” laser pulse, and a magnetic field which makes the Rb atoms precess about. When the image is absorbed into the atoms in the cell, the control beam is turned off. Image readout occurs in a sort of reverse process. 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 JQI image storage method represents a potentially important support for the establishment of quantum networks which will exploit quantum effects for computing, communications, and metrology.

Quentin Glorieux, Jeremy B. Clark, Alberto M. Marino, Zhifan Zhou, Paul D. Lett
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