Light, for some scientists, just moves too fast. They dream of using "slow light" to overcome limitations in everything from image processing to quantum computing. Now, two teams in the US have taken important steps towards these goals.

Light is good at carrying information in a digital system. The problem is storing that information: typically, digital devices do this by converting the light into electrical signals and then back into light again when it is needed, and this back-and-forth can degrade the quality of information. The solution could be slow light - light reined in to a fraction of its usual speed by exotic states of matter. The idea is to delay or even halt light, and extract information from it when required.

Now John Howell and his team at University of Rochester in New York have shown how delayed light can reliably transmit information. They encoded images digitally in pulses of light and passed the pulses through a hot vapour, which slowed the pulses to a tenth of their original speed. Then they used an array of micro-mirrors to reconstruct the images when the light emerged after delays of up to 10 nanoseconds - an eternity in imaging terms (Physical Review Letters, vol 98, p 043902).

Another team from Harvard University have stopped light, transferred its characteristics into matter and then back into light. Lene Hau and colleagues fired a laser pulse into a Bose-Einstein condensate (BEC) - a dense, ultra-cold cloud of atoms that are locked into the same quantum state - and shone a second "coupling" laser at the cloud to slow the first down to a mere 16 kilometres per hour. In this way the original kilometre-long pulse was compressed and contained within the 20-micrometre width of the condensate. When the lasers were switched off, the data in the light was left imprinted in the condensate. The atoms migrated slowly over to another BEC cloud and transferred the imprint into it. The researchers then turned the coupling laser back on and generated a new light pulse bearing the original information from the second BEC cloud (Nature, vol 445, p 623). "We can sculpt the optical information under full control as it is processed into matter, which is very easy to manipulate," says Hau.

"This is beautiful work," says Rochester team member Ryan Camacho. "We may be able to dramatically increase our image storage times by using similar processes."