Ground-state structure and stability of dipolar condensates in anisotropic traps

Dutta, Omjyoti; Meystre, Pierre

doi:10.1103/physreva.75.053604

Cited by 70 publications

(129 citation statements)

References 23 publications

Supporting

Mentioning

118

Contrasting

Order By: Relevance

“…We can estimate the characteristic length scale of the collapse structures from the homogeneous Bogoliubov spectrum (28). If p c is the critical momentum for which the dispersion relation passes through zero energy (which signifies the onset of dynamical instability), then we can expect the characteristic length scale to be l c = 2π /p c .…”

Section: A Length Scales For Collapsementioning

confidence: 99%

“…However, outside of this regime we saw evidence for adiabatic local collapse, which we attributed to the presence of a roton minimum in the excitation spectrum. The homogeneous dispersion relation (28) does not have a roton minimum and in order to introduce one it is necessary to explicitly include a trap in at least one dimension. In highly cigar-shaped or pancake-shaped systems the roton minimum occurs in the dispersion relation for lowenergy excitations along the weakly confined direction.…”

Section: A Length Scales For Collapsementioning

confidence: 99%

“…An important physical consequence of the "roton" minimum is that it can lead to density modulations in the ground state dipolar BEC [20,22,24,25,26,27,28]. However, the regions of parameter space where they occur are small and lie close to the unstable region [24,28]. It is therefore natural to ask if these characteristic density modulations form during collapse where they might be more readily visible.…”

mentioning

confidence: 99%

“…For example, when C dd > 0 the system can undergo global magnetostriction and elongate along the axis of polarization [13,15,16,34,35], tending towards a collapsed state of a line of end-to-end dipoles. However, the dipoles can also rearrange themselves locally [20,22,24,25,26,27,28] and in particular, in a pancake-shaped geometry for C dd > 0 a "red blood cell" density profile has been predicted [24]. If collapse is triggered suddenly, which we term nonadiabatic collapse, the system does not follow the ground state solutions and excitations play a role.…”

mentioning

confidence: 99%

See 3 more Smart Citations

Structure formation during the collapse of a dipolar atomic Bose-Einstein condensate

et al. 2009

View full text Add to dashboard Cite

We investigate the collapse of a trapped dipolar Bose-Einstein condensate. This is performed by numerical simulations of the Gross-Pitaevskii equation and the novel application of the ThomasFermi hydrodynamic equations to collapse. We observe regimes of both global collapse, where the system evolves to a highly elongated or flattened state depending on the sign of the dipolar interaction, and local collapse, which arises due to dynamically unstable phonon modes and leads to a periodic arrangement of density shells, disks or stripes. In the adiabatic regime, where ground states are followed, collapse can occur globally or locally, while in the non-adiabatic regime, where collapse is initiated suddenly, local collapse commonly occurs. We analyse the dependence on the dipolar interactions and trap geometry, the length and time scales for collapse, and relate our findings to recent experiments.PACS numbers: 03.75. Kk, 75.80.+q Wavepacket collapse is a phenomenon seen in diverse physical systems whose common feature is that they obey non-linear wave equations [1], e.g., in nonlinear optics [2], plasmas [3] and trapped atomic Bose-Einstein condensates (BECs) [4,5,6,7,8,9]. In the latter case, collapse occurs when the atomic interactions are sufficiently attractive. For the usual case of isotropic s-wave interactions experiments have demonstrated both global [5] and local collapse [7] depending upon, respectively, whether the imaginary healing length is of similar size or much smaller than the BEC [10]. During global collapse the monopole mode becomes dynamically unstable and the BEC evolves towards a point singularity, with the threshold for collapse generally exhibiting a weak dependence on trap geometry [11,12]. Local collapse occurs when a phonon mode is dynamically unstable such that the collapse length scale is considerably smaller than the BEC.Recently, the Stuttgart group demonstrated collapse in a BEC with dipole-dipole interactions, where the atomic dipoles were polarized in a common direction by an external field [8,9]. The long-range nature of dipolar interactions means that the Gross-Pitaevskii wave equation that governs the BEC is not only non-linear but also non-local [13,14,15,16]. On top of being long-range, dipolar interactions are also anisotropic, being attractive in certain directions and repulsive in others. This anisotropy has manifested itself experimentally in the stability of the ground state, which is strongly dependent on the trap geometry [8], and in the anisotropic collapse of the condensate [9]. Some uncertainty exists over the mechanism of collapse in these systems. In the latter experiment, striking images indicate that the condensate underwent global collapse, which is likely to have occurred through a quadrupole mode [16,17,18]. In the former experiment, however, recent theoretical results suggest that local collapse played a dominant role [19].A unique feature of trapped dipolar BECs in comparison to s-wave BECs is that they are predicted to exhibit minima in their excitation spec...

show abstract

Section: A Length Scales For Collapsementioning

confidence: 99%

Section: A Length Scales For Collapsementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Structure formation during the collapse of a dipolar atomic Bose-Einstein condensate

et al. 2009

View full text Add to dashboard Cite

show abstract

“…Another remarkable property of a dipolar BEC in a pancake-shaped trap is the existence of a roton minimum in its Bogoliubov spectrum [18]. Furthermore, close to the collapse threshold, the existence of structured ground states is predicted [28,29], a precursor for the supersolid phase [30] that is expected to appear in dipolar BECs in three dimensional optical lattices. Finally, a field that has gained increasing interest in the recent past is the study of unusual vortex lattice patterns in rotating dipolar BECs [31].…”

mentioning

confidence: 99%

Stabilization of a purely dipolar quantum gas against collapse

et al. 2008

View full text Add to dashboard Cite

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 ...

show abstract

Binary Mixture of Quasi-One-Dimensional Dipolar Bose–Einstein Condensates with Tilted Dipoles

Hocine

Benarous

2018

J Low Temp Phys

View full text Add to dashboard Cite

We consider a 168 Er-164 Dy dipolar mixture, trapped by a cigar shaped harmonic potential. We derive the quasi-1D inter-species effective potential exhibiting the tilting angles and show that it is a quite natural generalization of the situation of a single dipolar gas. By solving the coupled Gross-Pitaevskii equations, we observe a transition from miscible to immiscible mixture as the orientations of the magnetic moments are varied. The atom numbers are also shown to lead to noticeable effects on the mixture.

show abstract

Ground-state structure and stability of dipolar condensates in anisotropic traps

Cited by 70 publications

References 23 publications

Structure formation during the collapse of a dipolar atomic Bose-Einstein condensate

Structure formation during the collapse of a dipolar atomic Bose-Einstein condensate

Stabilization of a purely dipolar quantum gas against collapse

Binary Mixture of Quasi-One-Dimensional Dipolar Bose–Einstein Condensates with Tilted Dipoles

Contact Info

Product

Resources

About