Letters to Nature

Nature 409, 490-493 (25 January 2001) | doi:10.1038/35054017; Received 13 October 2000; Accepted 17 November 2000

Observation of coherent optical information storage in an atomic medium using halted light pulses

Chien Liu1,2, Zachary Dutton1,3, Cyrus H. Behroozi1,2 & Lene Vestergaard Hau1,2,3

  1. Rowland Institute for Science, 100 Edwin H. Land Boulevard, Cambridge, Massachusetts 02142, USA
  2. Division of Engineering and Applied Sciences,
  3. Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA

Correspondence to: Chien Liu1,2 Correspondence and requests for materials should be addressed to C.L. (e-mail: Email: chien@deas.harvard.edu).

Electromagnetically induced transparency1, 2, 3 is a quantum interference effect that permits the propagation of light through an otherwise opaque atomic medium; a 'coupling' laser is used to create the interference necessary to allow the transmission of resonant pulses from a 'probe' laser. This technique has been used4, 5, 6 to slow and spatially compress light pulses by seven orders of magnitude, resulting in their complete localization and containment within an atomic cloud4. Here we use electromagnetically induced transparency to bring laser pulses to a complete stop in a magnetically trapped, cold cloud of sodium atoms. Within the spatially localized pulse region, the atoms are in a superposition state determined by the amplitudes and phases of the coupling and probe laser fields. Upon sudden turn-off of the coupling laser, the compressed probe pulse is effectively stopped; coherent information initially contained in the laser fields is 'frozen' in the atomic medium for up to 1 ms. The coupling laser is turned back on at a later time and the probe pulse is regenerated: the stored coherence is read out and transferred back into the radiation field. We present a theoretical model that reveals that the system is self-adjusting to minimize dissipative loss during the 'read' and 'write' operations. We anticipate applications of this phenomenon for quantum information processing.