Dipolar condensates with tilted dipoles in a pancake-shaped confinement

Abstract

The effect of dipolar orientation with respect to the condensate plane on the mean-field dynamics of dipolar Bose-Einstein condensates in a pancake-shaped confinement is discussed. The stability of a quasi-two-dimensional condensate, with respect to the tilting angle, is found to be different from a two-dimensional layer of dipoles, indicating the relevance of the transverse extension while characterizing two-dimensional dipolar systems. An anisotropic excitation spectrum exhibiting a highly tunable, rotonlike minimum can arise entirely from the dipole-dipole interactions, by tilting the dipoles. At the magic angle and in the absence of contact interactions, the long-wavelength excitations are not phononlike and always unstable. The post-roton-instability dynamics, in contrast to phonon instability, in a uniform condensate, is featured by a transient, defect-free, stripe pattern, which eventually undergoes local collapses, and driving the condensate back into the stable regime can make them sustained for longer. Hopping between stripes has been observed before it melts into a uniform state in the presence of dissipation. Finally, we discuss a class of solutions, in which a quasi-two-dimensional condensate is self-trapped in one direction, as well as a regime of interaction parameters, including attractive short-range interactions, at which a two-dimensional anisotropic soliton can be stabilized, and we show that a chromium condensate with a relatively small number of atoms is well suited for this.Comment: 8 pages, 6 figure

Ground state of an ultracold Fermi gas of tilted dipoles in elongated traps

“…Here the anisotropies due to the harmonic trap are already taken into account and eliminated, so that only effects of the DDI contribute to the nontrivial value of δ xz and δ yz . This is in close analogy to the definition of the relative total energy shift of the system in (19), or the FS deformation in (20). In figure 7 we present the angular dependence of the relative cloud deformations for the Fermi gas of erbium with the same parameters as in figure 4(a).…”

“…Such species exhibit fascinating phenomena, such as the Rosensweig instability [8], the emergence of quantum-stabilised droplets [9][10][11] and roton quasiparticles [12]. Correspondingly, all these developments triggered much theoretical work, including, but not limited to, the numerical effort to simulate dipolar quantum gases in fully anisotropic traps [13][14][15][16][17], the roton instability in pancake-shaped condensates [18][19][20], the investigation of beyond-mean-field effects in onecomponent [21,22] and two-component [23] gases, the formation of the previously observed droplets [24][25][26], their ground-state properties and elementary excitations [27][28][29], the role of three-body interactions [30], and the self-bounded nature of the droplets [26].…”

Soliton Dimer-soliton scattering in coupled Quasi-one-dimensional Dipolar Bose-Einstein Condensates

“…The collisional dynamics between bright solitons is studied in condensates with both contact interactions [6,13,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] and dipoledipole interactions (DDIs) [29,[31][32][33][34][35][36][37][38][39][40], which have been exploited to generate entangled soliton pairs [17,18] and design interferometers [19,22,28,41,42]. Contrary to the short-range condensates, in dipolar BECs, the long range and anisotropic nature of DDI lead to novel scenarios such as the multi-dimensional solitons [43][44][45][46][47][48] and interlayer effects [49][50][51][52][53][54]. The latter include the stabilization of soliton complexes such as molecules or dimers, crystals and filaments…”

Magic tilt angle for stabilizing two-dimensional solitons by dipole-dipole interactions

“…Even though trapping potentials can be used to stabilize 3D or quasi-2D soliton condensates, dipolar BECs suffer from instabilities against spontaneous excitation of roton and phonon modes at high and low momenta, respectively [30][31][32][33][34][35], which manifest themselves at large strengths of DDI [36]. For matter waves trapped in a cigar-shaped potential, existence of stable quasi-1D solitons was predicted for combinations of the DDI and local interactions [37][38][39][40][41][42][43].…”