Light frozen in a hall of atomic mirrors

A few years ago, two different groups succeeded in slowing and then storing a pulse of light in atomic vapor. In that work, the properties of incoming photons were vested in the spin orientations of the atoms in the vapor; the light pulses no longer existed but could later be reconstituted into propagating light beams. A new experiment has brought light to a halt and left it intact as an optical entity. Harvard’s Mikhail Lukin and his colleagues began, as in the earlier work, by converting the incoming light pulse into a corresponding ensemble of spins in a gaseous medium. But then they brought a pair of counter-propagating control beams to bear on the medium. Those beams not only eased the optical pulse back into existence but also created a standing-wave pattern that generated spatially varying atomic absorption. The atoms then acted like a stack of mirrors that trapped the reconstituted electromagnetic radiation within a fixed stationary envelope. Thus the light pulse was literally frozen in space. When one of the control beams was turned off, the light traveled in the direction of the remaining beam. Lukin says that this work may lead to new nonlinear techniques for generating interactions between faint light beams. (M. Bajcsy, A. S. Zibrov, M. D. Lukin, Nature 426, 638, 2003.)