Have light, will not travel

Harvard researchers fired a short signal pulse of red laser light into a sealed glass cylinder containing a hot gas of rubidium atoms illuminated by a strong control beam. While the pulse was traveling through the rubidium gas, they switched off the control beam, resulting in the storage of a holographic imprint of the signal pulse on the rubidium atoms. Instead of using a single control beam to re-create and release the signal pulse, as was done in earlier experiments, the Harvard team used two counterpropagating control beams. Besides re-creating the signal pulse, the two control beams generate a standing-wave pattern of dark and bright regions. This light pattern makes the atoms behave like a stack of tiny mirrors. As the re-created signal pulse tries to propagate through this medium, the photons bounce back and forth in such a way that the overall pulse remains frozen in space. The pulse can be released again by switching off one of the control beams. The present work may yield new approaches to enhance interaction between faint light pulses, which could help process information carried by light pulses. An example of this would be quantum information processing – a powerful theoretical approach that uses single photons’ or atoms’ quantum states to store information.