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Register a new userCharacteristic features of the Shannon information entropy of dipolar Bose-Einstein condensates
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Added by
Paulsamy Muruganandam
Publication date
2017
fields
Physics
and research's language is
English
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Calculation of the Shannon information entropy (S) and its connection with the order-disorder transition, and with inter-particle interaction provide a challenging research area in the field of quantum information. Experimental progress with cold trapped atoms has corroborated this interest. In the present work, S is calculated for the Bose-Einstein condensate (BEC) with dominant dipolar interaction for different dipole strengths, trap aspect ratio and number of particles (N). Trapped dipolar bosons in an anisotropic trap provide an example of system where the effective interaction is strongly determined by the trap geometry. The main conlcusion of the present calculation is that the anisotropic trap reduces the number of degrees of freedom, resulting in more ordered configurations. The Landsbergs order parameter exhibits quick saturation with the increase in scattering length in both prolate and oblate traps. We also define the threshold scattering length which makes the system completely disordered. Unlike non-dipolar BEC in a spherical trap, we do not find a universal linear relation between S and ln N, and we, therefore, introduce a general quintic polynomial fit rather well working for a wide range of particle number.
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We have computed phase diagrams for rotating spin-1 Bose-Einstein condensates with long-range magnetic dipole-dipole interactions. Spin textures including vortex sheets, staggered half-quantum- and skyrmion vortex lattices and higher order topological defects have been found. These systems exhibit both superfluidity and magnetic crystalline ordering and they could be realized experimentally by imparting angular momentum in the condensate.
Vortices are expected to exist in a supersolid but experimentally their detection can be difficult because the vortex cores are localized at positions where the local density is very low. We address here this problem by performing numerical simulations of a dipolar Bose-Einstein Condensate (BEC) in a pancake confinement at $T=0$ K and study the effect of quantized vorticity on the phases that can be realized depending upon the ratio between dipolar and short-range interaction. By increasing this ratio the system undergoes a spontaneous density modulation in the form of an ordered arrangement of multi-atom droplets. This modulated phase can be either a supersolid (SS) or a normal solid (NS). In the SS state droplets are immersed in a background of low-density superfluid and the system has a finite global superfluid fraction resulting in non-classical rotational inertia. In the NS state no such superfluid background is present and the global superfluid fraction vanishes. We propose here a protocol to create vortices in modulated phases of dipolar BEC by freezing into such phases a vortex-hosting superfluid (SF) state. The resulting system, depending upon the interactions strengths, can be either a SS or a NS To discriminate between these two possible outcome of a freezing experiment, we show that upon releasing of the radial harmonic confinement, the expanding vortex-hosting SS shows tell-tale quantum interference effects which display the symmetry of the vortex lattice of the originating SF, as opposed to the behavior of the NS which shows instead a ballistic radial expansion of the individual droplets. Such markedly different behavior might be used to prove the supersolid character of rotating dipolar condensates.
Dipolar Bose-Einstein condensates represent a powerful platform for the exploration of quantum many-body phenomena arising from long-range interactions. A series of recent experiments has demonstrated the formation of supersolid states of matter. Subsequent theoretical works have shown that quantum fluctuations can affect the underlying phase transition and may lead to the emergence of supersolids with various lattice structures in dipolar condensates. In this work we explore the signatures of such different geometries in confined finite condensates. In addition to previously found triangular lattices, our analysis reveals a rich spectrum of states, from honeycomb patterns and ring structures to striped supersolids. By optimizing relevant parameters we show that transitions between distinct supersolids should be observable in current experiments.
We perform a full three-dimensional study on miscible-immiscible conditions for coupled dipolar and non-dipolar Bose-Einstein condensates (BEC), confined within anisotropic traps. Without loosing general miscibility aspects that can occur for two-component mixtures, our main focus was on the atomic erbium-dysprosium ($^{168}$Er-$^{164}$Dy) and dysprosium-dysprosium ($^{164}$Dy-$^{162}$Dy) mixtures. Our analysis for pure-dipolar BEC was limited to coupled systems confined in pancake-type traps, after considering a study on the stability regime of such systems. In case of non-dipolar systems with repulsive contact intneeractions we are able to extend the miscibility analysis to coupled systems with cigar-type symmetries. For a coupled condensate with repulsive inter- and intra-species two-body interactions, confined by an external harmonic trap, the transition from a miscible to an immiscible phase is verified to be much softer than in the case the system is confined by a symmetric hard-wall potential. Our results, presented by density plots, are pointing out the main role of the trap symmetry and inter-species interaction for the miscibility. A relevant parameter to measure the overlap between the two densities was defined and found appropriate to quantify the miscibility of a coupled system.
We explore spatial symmetry breaking of a dipolar Bose Einstein condensate in the thermodynamic limit and reveal a critical point in the phase diagram at which crystallization occurs via a second order phase transition. This behavior is traced back to the significant effects of quantum fluctuations in dipolar condensates, which moreover stabilize a new supersolid phase, namely a regular honeycomb pattern with maximal modulational contrast and near-perfect superfluidity.
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