Structural transitions of nearly second order in classical dipolar gases

Cartarius, Florian; Morigi, Giovanna; Minguzzi, Anna

doi:10.1103/physreva.90.053601

Cited by 7 publications

(6 citation statements)

References 46 publications

(81 reference statements)

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“…In the presence of an external field chains, columns, sheets, bent walls, lamellar, labyrinthine or worm-like structures, and hexagonal structures all appear [68]. Transitions from single chains to double chains (zig-zag) can also occur if initially strong transverse confinement is reduced [69].…”

Section: Classical Ferrofluids and Strongly Correlated Quantum Ferrofmentioning

confidence: 99%

Vortices and vortex lattices in quantum ferrofluids

Martin

Marchant

O’Dell

et al. 2017

J. Phys.: Condens. Matter

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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.

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Section: Classical Ferrofluids and Strongly Correlated Quantum Ferrofmentioning

confidence: 99%

Vortices and vortex lattices in quantum ferrofluids

Martin

Marchant

O’Dell

et al. 2017

J. Phys.: Condens. Matter

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“…We remark that the Ginzburg criterion can be straightforwardly generalized to all dimensions D < D * as well as to other types of phase transition characterized by an upper critical dimension. Our treatment could be extended to encompass quench dynamics at finite temperatures [35], where scattering between defects during the quenches affect the resulting scaling [58], and across phase transitions which are weakly first order (nearly second order) [59,60]. We further notice that our numerical setup allows us to further explore the dynamics indicated in recent theoretical works, which went beyond the KZ theory and analysed relaxation after quenches [61,62].…”

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confidence: 99%

Crossover from Classical to Quantum Kibble-Zurek Scaling

et al. 2016

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The Kibble-Zurek (KZ) hypothesis identifies the relevant time scales in out-of-equilibrium dynamics of critical systems employing concepts valid at equilibrium: It predicts the scaling of the defect formation immediately after quenches across classical and quantum phase transitions as a function of the quench speed. Here we study the crossover between the scaling dictated by a slow quench, which is ruled by the critical properties of the quantum phase transition, and the excitations due to a faster quench, where the dynamics is often well described by the classical model. We estimate the value of the quench rate that separates the two regimes and support our argument using numerical simulations of the out-of-equilibrium many-body dynamics. For the specific case of a φ 4 model we demonstrate that the two regimes exhibit two different power-law scalings, which are in agreement with the KZ theory when applied to the quantum and to the classical case. This result contributes to extending the prediction power of the Kibble-Zurek mechanism and to provide insight into recent experimental observations in systems of cold atoms and ions.

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“…One contribution leads to the interaction term H (j,j+1) int of the ϕ 4 model. The other is a coupling between axial and transverse modes, which becomes relevant when the chain is compressible [20]. When the chain is incompressible, for hard-core bosons and unit filling the action of Hamiltonian H y + H xy can be reduced to an effective ϕ 4 model and the linear-zigzag transition is of the same universality class of the Ising model in transverse field [19,25].…”

Section: Coupling Between Axial and Transverse Degrees Of Freedommentioning

confidence: 99%

“…For an incompressible chain the transition is continuous and the classical order parameter is the transverse displacement [16][17][18], while the quantum linear-zigzag transition is of the same universality class as the Ising model in transverse field [19]. When the chain is compressible, instead, the classical transition becomes of weak first order [20], while the corresponding quantum behaviour is yet unexplored. In these respects the model we consider is peculiar, since the compressibility results from the interplay between interactions and quantum fluctuations and can be thus tuned by changing the lattice depth of the transverse confinement.…”

Section: Introductionmentioning

confidence: 99%

Multimode Bose-Hubbard model for quantum dipolar gases in confined geometries

2017

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We theoretically consider ultracold polar molecules in a wave guide. The particles are bosons, they experience a periodic potential due to an optical lattice oriented along the wave guide and are polarised by an electric field orthogonal to the guide axis. The array is mechanically unstable by opening the transverse confinement in the direction orthogonal to the polarizing electric field and can undergo a transition to a double-chain (zigzag) structure. For this geometry we derive a multi-mode generalized Bose-Hubbard model for determining the quantum phases of the gas at the mechanical instability taking into account the quantum fluctuations in all directions of space. Our model limits the dimension of the numerically relevant Hilbert subspace by means of an appropriate decomposition of the field operator, which is obtained from a field theoretical model of the linearzigzag instability. We determine the phase diagrams of small systems using exact diagonalization and find that, even for tight transverse confinement, the aspect ratio between the two transverse trap frequencies controls not only the classical but also the quantum properties of the ground state in a non-trivial way. Convergence tests at the linear-zigzag instability demonstrate that our multi-mode generalized Bose-Hubbard model can catch the essential features of the quantum phases of dipolar gases in confined geometries with a limited computational effort. arXiv:1704.00948v1 [cond-mat.quant-gas]

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Structural transitions of nearly second order in classical dipolar gases

Cited by 7 publications

References 46 publications

Vortices and vortex lattices in quantum ferrofluids

Vortices and vortex lattices in quantum ferrofluids

Crossover from Classical to Quantum Kibble-Zurek Scaling

Multimode Bose-Hubbard model for quantum dipolar gases in confined geometries

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