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A while ago an experiment demonstrated that it is possible to stop a light pulse in a supercooled sodium cloud, store the data contained within it, and totally extinguish it, only to reincarnate the pulse in another cloud two-tenths of a millimeter away.

light

Most of the papers discussing the details of this experiment are behind paywalls. I understand the setup that the light pulse can be revived, and its information transferred between the two clouds of sodium atoms, by converting the original optical pulse into a traveling matter wave which is an exact matter copy of the original pulse, traveling at a leisurely 200 meters per hour. The matter pulse is readily converted back into light when it enters the second of the supercooled clouds -- known as Bose-Einstein condensates -- and is illuminated with a control laser.

The key as I understand it is the Bose-Einstein condensates (BEC) become phase-locked. The light drives a controllable number of the condensate's roughly 1.8 million sodium atoms to enter into quantum superposition states with a lower-energy component that stays put and a higher-energy component that travels between the two BECs. The amplitude and phase of the light pulse stopped and extinguished in the first cloud are imprinted in this traveling component and transferred to the second cloud, where the recaptured information can recreate the original light pulse.

How does matter become "phased locked" to light and how do all these atoms contain the "information" of the light to reproduce it? And what is this talk of separating lower/higher energy components?

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    $\begingroup$ This paper ? $\endgroup$ – Trimok Dec 3 '13 at 17:59
  • $\begingroup$ arxiv.org then click "find." Formatted preprints of papers are permanently archived. arXiv:1234.5678 translates to arxiv.org/abs/1234.5678, then view the PDF. For DOI:, dx.doi.org Knowledge wants to be free. $\endgroup$ – Uncle Al Feb 6 '14 at 15:25
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Never worked with BEC but for ordinary matter it works like this: The incoming field makes the electrons oscillate with the same phase and frequency as the driving field (superposition state). If this state emits radiation before any kind of dephasing (usually takes femto/picoseconds) the outgoing field will be a copy of the incoming field.

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