Ultracold Dipolar Gases – a Challenge for Experiments and Theory

Baranov, M. A.; Dobrek, Ł.; Góral, Krzysztof; Santos, Luís; Lewenstein, Maciej

doi:10.1142/9789812791269_0013

Cited by 24 publications

(31 citation statements)

References 49 publications

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“…As the DDI tends to elongate the BEC along the z-direction and shrink it radially, it is clear that the desired trap is oblate. Using our model we obtain the criterion λ > λ c ≈ 5.2 for a purely dipolar BEC to be stable, a result that agrees well with the values found in [13,14,26]. The grey curve in Fig.…”

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confidence: 86%

Stabilization of a purely dipolar quantum gas against collapse

et al. 2008

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We report on the experimental observation of the dipolar collapse of a quantum gas which sets in when we reduce the contact interaction below some critical value using a Feshbach resonance. Due to the anisotropy of the dipole-dipole interaction, the stability of a dipolar Bose-Einstein condensate depends not only on the strength of the contact interaction, but also on the trapping geometry. We investigate the stability diagram and find good agreement with a universal stability threshold arising from a simple theoretical model. Using a pancake-shaped trap with the dipoles oriented along the short axis of the trap, we are able to tune the scattering length to zero, stabilizing a purely dipolar quantum gas.Interactions between atoms dominate most of the properties of quantum degenerate gases [1]. In the ultracold regime these interactions are usually well described by an effective isotropic zero-range potential. The strength and sign of this contact interaction is determined by a single parameter, the scattering length a. The contact interaction is responsible for a variety of striking properties of quantum gases. Strongly influencing the excitation spectrum of the condensate it gives rise to e.g. the superfluidity of Bose-Einstein condensates (BEC) or the existence of vortex lattices. The contact interaction also plays a crucial role in the physics of strongly correlated systems like in the BEC-BCS crossover [2] or in quantum phase transitions like the Mott insulator transition [3].Another fundamental topic is the question of the existence of a stable ground state depending on the modulus and sign of the contact interaction. In the homogeneous case repulsive contact interaction (a > 0) is necessary for the stability of the BEC. In contrast, if the contact interaction is attractive (a < 0), the BEC is unstable. This instability can be prevented by an external trapping potential. The tendency to shrink towards the center of the trap is in that case counteracted by the repulsive quantum pressure arising from the Heisenberg uncertainty relation. Detailed analysis [4] yields that a condensate is stable as long as the number of atoms N in the condensate stays below a critical value N crit given bywhere a ho is the harmonic oscillator length and k is a constant on the order of 1/2. This scaling, as well as the collapse dynamics for N > N crit , have been studied experimentally with condensates of 7 Li [5, 6] and 85 Rb [7,8]. In [9, 10] the atom number dependance of the collapse of mixtures of bosonic 87 Rb and fermionic 40 K quantum gases has been investigated. Being anisotropic and long-range, the dipole-dipole interaction (DDI) differs fundamentally from the contact interaction. Besides many other properties, the stability condition therefore changes in a system with a DDI present. Considering the case of a purely dipolar condensate with homogeneous density polarized by an external field, one finds that due to the anisotropy of the DDI, the BEC is unstable, independent of how small the dipole moment is [11]. As in the ...

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confidence: 86%

Stabilization of a purely dipolar quantum gas against collapse

et al. 2008

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“…The anisotropic, long-range, dipole-dipole interaction is predicted to give rise to new and rich physics in these cold dipolar gases. 78 Low Temperatures and Cold Molecules Downloaded from www.worldscientific.com by WEIZMANN INSTITUTE OF SCIENCE on 06/10/16. For personal use only.…”

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confidence: 99%

Manipulation of Molecules with Electric Fields

Meerakker

Bethlem

Meijer

2008

Low Temperatures and Cold Molecules

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“…Es wird theoretisch vorhergesagt, dass die anisotropen, langreichweitigen DipolDipol-Wechselwirkungen zwischen kalten polaren Molekülen zu einer neuen und reichen Physik in diesen kalten dipolaren Gasen führen. [152][153][154] Erste Hinweise darauf gab es durch die Bildung eines Bose-Einstein-Kondensats aus Chrom-Atomen mit magnetischen Dipol-Dipol-Wechselwirkungen. [155,156] Zwischen elektrischen Dipolen treten sehr starke Wechselwirkungen auf.…”

Section: Phänomene Bei Sehr Tiefen Temperaturenunclassified

Kalte Moleküle: Herstellung, Anwendungen und Herausforderungen

Schnell

Meijer

2009

Angewandte Chemie

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Die Forschung an kalten Molekülen hat sich in den letzten Jahren rasant entwickelt. Es gibt mittlerweile eine Reihe etablierter Methoden, um Moleküle in der Gasphase auf Temperaturen im Millikelvin‐Bereich zu kühlen. Dennoch konzentriert sich ein Schwerpunkt der aktuellen Forschung darauf, neue Wege zu finden, um die Temperaturen der Moleküle dem absoluten Nullpunkt noch näher zu bringen. Proben kalter Moleküle bieten nicht nur wichtige Anwendungen für die hochauflösende Spektroskopie, die von den verlängerten Wechselwirkungszeiten der langsamen Moleküle mit der elektromagnetischen Strahlung profitiert. Sie versprechen auch einen Zugang zu einem exotischen Regime der chemischen Reaktivität, in dem Phänomene wie Quantentunneln und ‒resonanzen vorherrschen. Dieser Aufsatz beginnt mit einer Einführung in die Methoden, mit denen kalte Moleküle hergestellt werden können, mit besonderem Schwerpunkt auf der Stark‐Abbremsung und auf Molekülfallen. Ein wichtiger Teil des Aufsatzes ist neben den teilweise bereits realisierten auch den zukünftig möglichen Anwendungen kalter Moleküle gewidmet, die beide mithilfe ausgewählter Beispiele näher beleuchtet werden.

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Ultracold Dipolar Gases – a Challenge for Experiments and Theory

Cited by 24 publications

References 49 publications

Stabilization of a purely dipolar quantum gas against collapse

Stabilization of a purely dipolar quantum gas against collapse

Manipulation of Molecules with Electric Fields

Kalte Moleküle: Herstellung, Anwendungen und Herausforderungen

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