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Pancake Shape Prevents Collapse Of Quantum Gases

Date:
February 28, 2008
Source:
University of Stuttgart
Summary:
Instabilities in clouds of attracting matter are a well known phenomenon. In astrophysics, they lead to spectacular effects such as supernovae. But also in a gas, when it is made up of tiny atomic magnets, the magnetic forces lead to instabilities. Such a gas cloud implodes due to the attractive interaction between the magnetic atoms. The finding that attracting matter is unstable is known to everybody who has ever played with a bunch of magnets: they simply clump together.
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Chromium atoms are cooled down to below one MicroKelvin by blue lasers. At such low temperatures a quantum gas of magnets is formed.
Credit: University of Stuttgart

Instabilities in clouds of attracting matter are a well known phenomenon. In astrophysics, they lead to spectacular effects such as supernovae. But also in a gas, when it is made up of tiny atomic magnets, the magnetic forces lead to instabilities. Such a gas cloud implodes due to the attractive interaction between the magnetic atoms. The research group of Professor Tilman Pfau of the 5th Institute of Physics at the University of Stuttgart have recently measured the complete stability diagram of such a gas of magnets which maps exactly the border between stable and unstable states of the gas.

The finding that attracting matter is unstable is known to everybody who has ever played with a bunch of magnets: they simply clump together. Even when they are aligned in parallel the same happens - unless the magnets are, at the same time, forced to stay in a plane. Such an arrangement in a pancake-like shape – in contrast to a spherical or cigar-like geometry – is stable. In the case of these spheres or cigars, only an additional repulsive interaction between the atoms that keeps them apart could prevent the whole system from collapsing (clumping together).

Tilman Pfau’s group are investigating the properties of so called “quantum gases” in the framework of their trans-regional collaborative research centre (SFB/TRR21 “Control of quantum correlations in tailored matter –Co.Co.Mat.” ). The gas in which the above experiments were performed consists of chromium atoms that are forced to undergo a phase transition to a so called Bose-Einstein condensate at extremely low temperatures.

In this special state of quantum matter, the interactions as well as the shape of the trap that holds the atomic cloud and squeezes it into the desired shape can be controlled very precisely. Ten years ago Tilman Pfau, together with a group of polish scientists,  had predicted theoretically the border between stable and unstable conditions. Only now could his group show experimentally that the gas behaves as had been predicted and that it is indeed stabilized by forcing it into a plain pancake shape.

In their ongoing research project, the group are having a closer look at the dynamics of the collapse itself. Due to its similarity to a supernova, this collapse is sometimes called “Bose Nova”. During the collapse the researchers expect for certain parameters the occurrence of new states of quantum matter caused by the magnetic interaction. An exactly controlled and triggered collapse could – on the other hand – also be used to deposit precisely focused chromium atoms on a surface.

Journal reference: Tobias Koch, Thierry Lahaye, Jonas Metz, Bernd Fröhlich, Axel Griesmaier, Tilman Pfau: „Stabilizing a purely dipolar quantum gas against collapse", Nature Physics (2008), DOI number 10.1038/nphys887 [arXiv:cond-mat 0710.3643]


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The above post is reprinted from materials provided by University of Stuttgart. Note: Materials may be edited for content and length.


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University of Stuttgart. "Pancake Shape Prevents Collapse Of Quantum Gases." ScienceDaily. ScienceDaily, 28 February 2008. <www.sciencedaily.com/releases/2008/02/080226170616.htm>.
University of Stuttgart. (2008, February 28). Pancake Shape Prevents Collapse Of Quantum Gases. ScienceDaily. Retrieved August 30, 2015 from www.sciencedaily.com/releases/2008/02/080226170616.htm
University of Stuttgart. "Pancake Shape Prevents Collapse Of Quantum Gases." ScienceDaily. www.sciencedaily.com/releases/2008/02/080226170616.htm (accessed August 30, 2015).

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