IT鈥橲 like catching a moonbeam 鈥� using a cloud of vapour to capture images made of light itself. Right now, the result looks like something you鈥檇 see on a faulty LED display, but it could one day form the basis of a new type of computer memory.
First, rubidium atoms are exposed to a 鈥減ump鈥� laser, putting them into an excited quantum state. This makes them transparent to pulses of light from a second laser, known as the 鈥減robe鈥� beam, which carries information such as an image formed by shining the beam through a mask.
When the beams are turned off the atoms de-excite, at which point the final pulse of the probe beam is absorbed. This leaves an imprint in the atoms鈥� quantum states, which turns back into light when the pump beam is switched back on, allowing the image to be recovered. Since information is being stored and retrieved, this amounts to a new form of optical computer memory.
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Previous attempts have only managed to store a single blurry spot of light, but now a team from the Israel Institute of Technology (Technion) in Haifa and the Weizmann Institute of Science in Rehovot, Israel, has managed to store relatively sharp 2-millimetre images of numbers for up to 30 microseconds.
A major obstacle was that atoms in the vapour tended to diffuse, blurring the recovered image. To get round this, the team altered the phase of the light across the image in such a way that if two atoms storing different areas of the image mix through diffusion, the light waves recovered from them will be of opposite phase, cancelling each other out in the recaptured image (Physical Review Letters, ).
鈥淭his is an excellent step towards future dreams of all-optical memory devices,鈥� says Barry Garraway, a physicist at the University of Sussex, UK, although he adds that more work is needed to make the image sharper and more stable.
