Light slowed and stored in a solid

The group velocity of light—the speed at which the wave pulse propagates—can be considerably lowered, even to zero, in a medium having an index of refraction that changes dramatically with wavelength. The energy and information in the original light pulse can be stored, without any heating, in the form of coherent spin excitations in the atoms of the medium. Last year, two different experiments stopped and stored light in a vapor sample (see Physics Today, March 2001, page 17 ). Now the feat has been carried out in a 3-mm-thick crystal—yttrium silicate doped with atoms of the rare earth praseodymium—already in common use for high-density optical data storage. The experiment was carried out at MIT and at the Air Force Research Laboratory in Hanscom, Massachusetts. The researchers foresee many applications in areas such as quantum computing, ultrasensitive magnetometry, and acousto-optics. (A. V. Turukhin et al., Phys. Rev. Lett. 88 , 023602, 2001 http://dx.doi.org/10.1103/PhysRevLett.88.023602 .)