Researchers at the Rowland Institute of Science (Cambridge, MA) and Harvard University (Cambridge, MA) have been radically slowing light by passing it through a specially prepared Bose-Einstein condensate (BEC; a cooled cloud of atoms all in the same quantum state). Now they have beaten their own record, reducing the velocity of light further to a speed of 0.44 m/s, or 1 mph. They use both a coupling and a probe laser beam to achieve electromagnetically induced transparency in a sodium BEC, which produces a slowing of the probe beam. The new results come from the use of two separate wavelengths for the two beams, rather than one, allowing the use of the sodium D2 line for coupling and the sodium D1 line for the probe and thus reducing losses.
The next step will be to slow the light in the BEC down to 1 cm/s, says Lene Hau, principal investigator. This is the point where the speeds of sound and light are equal, allowing atoms to ride along on the light pulses. Such a phenomenon could permit the creation of low-power nonlinear optical devices. By combining such high nonlinearities with nanostructures, tiny optical switches might be made that change states when influenced by as few as two photons, says Hau. Contact Lene Hau at [email protected].--Hassaun Jones-Bey