Vortices and vortex lattices in quantum ferrofluids

Abstract

The experimental realization of quantum-degenerate Bose gases made of atoms with sizeable magnetic dipole moments has created a new type of fluid, known as a quantum ferrofluid, which combines the extraordinary properties of superfluidity and ferrofluidity. A hallmark of superfluids is that they are constrained to rotate through vortices with quantized circulation. In quantum ferrofluids the long-range dipolar interactions add new ingredients by inducing magnetostriction and instabilities, and also affect the structural properties of vortices and vortex lattices. Here we give a review of the theory of vortices in dipolar Bose-Einstein condensates, exploring the interplay of magnetism with vorticity and contrasting this with the established behaviour in non-dipolar condensates. We cover single vortex solutions, including structure, energy and stability, vortex pairs, including interactions and dynamics, and also vortex lattices. Our discussion is founded on the mean-field theory provided by the dipolar Gross-Pitaevskii equation, ranging from analytic treatments based on the Thomas-Fermi (hydrodynamic) and variational approaches to full numerical simulations. Routes for generating vortices in dipolar condensates are discussed, with particular attention paid to rotating condensates, where surface instabilities drive the nucleation of vortices, and lead to the emergence of rich and varied vortex lattice structures. We also present an outlook, including potential extensions to degenerate Fermi gases, quantum Hall physics, toroidal systems and the Berezinskii-Kosterlitz-Thouless transition.

Real time observation of a stationary magneton

“…This discovered, QFM or else Quantum Magnet, vortex flux could also provide a possible physical mechanism for explaining the macroscopic field imprint of magnetic dipoles as shown in fig.2. The effect is similar as described by vortex hydrodynamics [18][19][20], quantum Bose-Einstein condensate ferrofluids [21] and general vortex model theory [22,23] very often encountered in nature from the quantum scale to the macro world [13]. The quantum vortex flux we call, M-field shown in fig.2(a) with red and fig.…”

“…The ferrolens optic display device is an electric insulator at all temperatures therefore not a superconductor. In addition we tested rigorously for superfluidic behavior concerning quantization of magnetic vortices generation at different values of induced angular momentum [21] [39] without any observable effect.…”

Vortex lattice formation in dipolar Bose-Einstein condensates via rotation of the polarization

“…Finally, by t = 5000ω −1 ⊥ the vortices have entered the condensate and have relaxed into a triangular Abrikosov vortex lattice. Several theoretical studies have indicated that this may be the ground state for a system of vortices in (non-)dipolar BECs at finite rotation frequencies [35,36,38,42,43,46,70]. In nondipolar BECs subject to a ramping up of the trapping rotation frequency, a vortex lattice is seen to form following a period of evolution of the nondipolar GPE at constant rotation frequency after the vortex instability has been triggered [66,71].…”

“…Examples of the methods that experimentalists have used to create vortices include: direct imprinting of phase defects into the condensate [29], rotation of either a laser * srivatsa.badariprasad@unimelb.edu.au beam stirrer or the external trapping potential of the condensate itself [30,31], dragging a barrier through the condensate [27,28,32], applying a rapidly oscillating perturbation to the trapping potential [25], Bose-condensing a rotating normal Bose gas [33], and utilising the Kibble-Zurek mechanism to trigger the formation of topological defects [34]. While vortices have not yet been experimentally observed in dipolar BECs, there exists an extensive body of theoretical research regarding vortex structure, vortex lattice structure, and vortex-vortex interactions in these systems [35][36][37][38][39][40][41][42][43][44][45][46].…”

Instability of Rotationally Tuned Dipolar Bose-Einstein Condensates

“…Dipolar Bose-Einstein condensates (BECs) have proved to be a unique, highly-controllable platform for studying the interplay of quantum many-body physics and magnetic interactions [1][2][3][4][5][6]. Compared to conventional condensates, in which the atoms undergo shortrange, contact-like, isotropic inter-particle interactions, a dipolar BEC also enjoys a long-range anisotropic dipoledipole interaction (DDI) [7][8][9][10][11]. While the first dipolar BECs were realised in a gas of 52 Cr [1,2], atoms with larger magnetic dipole moments such as 164 Dy [4,6] and 168 Er [5] have now been cooled to form strongly dipolar BECs.…”