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2012-02-01 [ ]

Atom laser with a hiccup

Ein Bose-Einstein-Kondensat fällt nach unten, expandiert dabei und wird in einer dünnen Schicht aus Licht vermessen.

Thorsten Schumm, Christian Koller, Aurelien Perrin, Stephanie Manz (v.l.n.r.)

The light of a laser and a norbal bulb differ not only in their obvious properties like intensity, color, collimation but also down tot he quantum level of individual photons. The famous Hanbury-Brown-Twiss experiment from the 60th showed that photons in a laser are distributed with equal probability across the beam, while in classical light they dend to „bunch“ to pairs. This is mathematically represented by the correlation function, a value of 1 means equal distribution while a value of 2 indicated bunching.

Similar investigations have recently been performed on matter waves of neutral atoms. At extremely low temperatures (1 millikelvin) a bosonic gas undergoes a transition into a collective state of matter – the Bose-Einstein condensate – which behaves quite similar to a laser.

The group of Prof. Schmiedmayer now performed the Hanbury-Brown-Twiss experiments across the transition from a classical gas to a Bose-Einstein condensate. They discovered a strong deviation from the analogy with light: not only does the correlation function change smoothly instead oft he expected sudden transition, it also shows a complex behaviour and even takes values below 1. The reason for this are – in contrast to photons – interactions between the atoms and the finite temperature oft he system. 

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