Spatially addressable readout and erasure of an image in a gradient echo memory
Last year Paul Lett and his JQI colleagues reported the ability to store a sequence of images (two letters of the alphabet) which were separated in time but overlapping in space within the volume of a gas-filled memory cell. This is random access in time. In a new experiment, by contrast, parts of a single image (spread out across a volume of space) can be stored and later recovered in chunks. Selectively reading out these partial views represents random access memory in space. Before, the storage could be called “temporal multiplexing,” while now it can be called “spatial multiplexing.”
In the new experiment the image is read out in three distinct parts one after the other by making the “control” beam more complex, delivering its light using additional mirrors and fibers. This serves to excite different parts of the vapor selectively.
The image is held by moving some atoms in the vapor into different stable states. The sections of the image can be read out over a period of microseconds. Portions of the image can also be deleted with what the researchers call an optical eraser.