More Strange Bose-Einstein Condensate Behavior

Allen Varney writes "According to a story on EurekAlert, an arXiv preprint server paper titled 'Scattering of atoms on a Bose-Einstein Condensate' reports that atoms striking a BEC sometimes appears to leave before they enter. 'This doesn't imply a breaking of the light-speed barrier, time travel or anything overly exotic but is a property of waves being broken down into component parts and being reassembled slightly differently. [...] As an atom hits the BEC, it is absorbed into the collective state but still exists as a vibration. The vibration travels through the BEC but can escape as an atom once more. The study reinforces the similarity between atoms as waves and light as waves.' Slashdot has talked about supposed faster-than-light travel once or twice (or more) before."

Comments

good explanation of particle/wave duality

[shiafu]

Stephen Hawking explains these concepts marvellously in his book, A Brief History of Time. It's an easy read, but also very informative.

A couple of points

[doru]

First of all, this is a theoretical paper, they do not detect anything.

Second, there's no "magic" in it. As they say in the article, the peak of the transmitted wavepacket appears before the peak of the incident wavepacket has reached the condensate.

At the beginning of the century (1914), Brillouin and Sommerfeld already showed that, when a plane EM wave with a sharp forward front propagating in vacuum is incident upon a transparent medium, its shape is changed and precursor waves form, with a velocity approaching c in vacuum, corresponding to the high-frequency components for which the (relative) permittivity goes to 1.

In excitable media (and I assume the same happens with atoms in a BEC) the effect is even more spectacular, because these fast components (or, as in this case, the leading edge of the pulse) can get amplified and then leave the medium before the "bulk" of the incoming pulse even enters it.

Moreover, before leaving the medium this "fast" pulse is split in two, and the reflected component can interfere destructively with the "lazy" pulse, wiping it out. Hence the "illusion". Needless to say, Einstein is still right :-)