Slowed Light Handed Off

Several years ago, physicists gained the ability to slow a beam of light in a gas of atoms; by manipulating the atoms' spins the energy of and information contained in the light could be transferred to the atoms in a coherent way (see PNU 521). By turning on additional laser beams, the original light signal, which we can think of as having been idling or temporarily stored in the atom cloud, could be reconstituted and sent on its way.

Now, one of the first researchers to slow light, Lene Hau of Harvard, has added an extra layer to this story. She and her colleagues, halting and storing a light signal in a gas of cold atoms-in this case a Bose-Einstein condensate (BEC) of sodium atoms-then transfer the signal, now in the form of a coherent pulse of atom waves rather than light waves, into a second BEC of sodium atoms some 160 microns away, from which, finally, the signal is revived as a conventional light pulse.

This feat, the sharing around of quantum information in light-form and in not just one but two atom-forms, offers great encouragement to those who hope to develop quantum computers.

Ginsberg et al., Nature, 8 February 2007