Large amplitude spin waves in ultra-cold gases

Fuchs, Jean-Noël; Gangardt, D. M.; Laloë, Franck

doi:10.1140/epjd/e2003-00219-1

Cited by 16 publications

(15 citation statements)

References 43 publications

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“…Spin waves. Spin waves have been studied extensively in both Bose and Fermi gases (21,22,24,(30)(31)(32)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52). Transverse spin waves arise from the identical spin rotation effect (ISRE, see §2.1.2 below).…”

Section: Spin Hydrodynamicsmentioning

confidence: 99%

Universal Spin Transport and Quantum Bounds for Unitary Fermions

Enss

Thywissen

2019

Annu. Rev. Condens. Matter Phys.

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We review recent advances in experimental and theoretical understanding of spin transport in strongly interacting Fermi gases. The central new phenomenon is the observation of a lower bound on the (bare) spin diffusivity in the strongly interacting regime. Transport bounds are of broad interest for the condensed matter community, with a conceptual similarity to observed bounds in shear viscosity and charge conductivity. We discuss the formalism of spin hydrodynamics, how dynamics are parameterized by transport coefficients, the effect of confinement, the role of scale invariance, the quasi-particle picture, and quantum critical transport. We conclude by highlighting open questions, such as precise theoretical bounds, relevance to other phases of matter, and extensions to lattice systems. 1 arXiv:1805.05354v1 [cond-mat.quant-gas]

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Section: Spin Hydrodynamicsmentioning

confidence: 99%

Universal Spin Transport and Quantum Bounds for Unitary Fermions

Enss

Thywissen

2019

Annu. Rev. Condens. Matter Phys.

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“…We obtain an explicit expression for the collision term in (1) using the method originally developed by Lhuillier and Laloë [43,44,46] for transport properties in Helium. In this approach, collisions are treated as single "atomic beam" experiments, where the colliding particles are assumed to be uncorrelated before and after a collision, reminiscent of Boltzmann's original molecular chaos hypothesis, but the scattering process itself is treated on a full quantum level.…”

Section: Relaxation Processes In a Large-spin Systemmentioning

confidence: 99%

“…We remedy this problem by choosing a cutoff |k | < M g S 2 2 , which is the distance between zero and the maximum of the imaginary part of the T -matrix (see Appendix D for more details). This step is unnecessary in the 3D case discussed by Lhuillier and Laloë [43,44,46]. The result is then given by…”

Section: Microscopic Derivation Of a Large-spin Boltzmann Equationmentioning

confidence: 99%

Relaxation Dynamics of an Isolated Large-Spin Fermi Gas Far from Equilibrium

et al. 2014

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A fundamental question in many-body physics is how closed quantum systems reach equilibrium. We address this question experimentally and theoretically in an ultracold large-spin Fermi gas where we find a complex interplay between internal and motional degrees of freedom. The fermions are initially prepared far from equilibrium with only a few spin states occupied. The subsequent dynamics leading to redistribution among all spin states is observed experimentally and simulated theoretically using a kinetic Boltzmann equation with full spin coherence. The latter is derived microscopically and provides good agreement with experimental data without any free parameters. We identify several collisional processes that occur on different time scales. By varying density and magnetic field, we control the relaxation dynamics and are able to continuously tune the character of a subset of spin states from an open to a closed system.

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“…The time-evolution of the distribution function f s (r, p, t) is given by the Boltzmann equation, (1) where the left-hand side represents the propagation of the atoms in the potential and the right-hand side stands for the collision integral,…”

Section: Lobomentioning

confidence: 99%

“…Understanding the spin relaxation, diffusion and other transport properties is of fundamental importance in such fields. In atomic gases it has been studied mainly in spinor Bose gases [1,2]. There has been a renewed interest in spin transport in Fermi gases which are a clearer parallel to electronic systems [3][4][5][6][7][8].…”

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confidence: 99%

Collision of two spin-polarized fermionic clouds

2011

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We study the collision of two spin-polarized Fermi clouds in a harmonic trap using a simulation of the Boltzmann equation. As observed in recent experiments, we find three distinct regimes of behavior. For weak interactions the clouds pass through each other. If interactions are increased they approach each other exponentially and for strong interactions they bounce off each other several times. We thereby demonstrate that all these phenomena can be reproduced using a semiclassical collisional approach and that these changes in behavior are associated with an increasing collision rate. We then show that the oscillation of the clouds in the bounce regime is an example of an unusual case in quantum gases: a nonlinear coupling between collective modes, namely, the spin dipole mode and the axial breathing mode, which is enforced by collisions. We also determine the frequency of the bounce as a function of the final temperature of the equilibrated system. Recently, spin transport has become a much studied field in solid-state systems, for example, in mesoscopic phenomena, where the electronic spin degree of freedom is used to create new devices. Understanding the spin relaxation, diffusion, and other transport properties is of fundamental importance in such fields. In atomic gases it has been studied mainly in spinor Bose gases [1,2]. There has been renewed interest in spin transport in Fermi gases which are a clearer parallel to electronic systems [3][4][5][6][7][8]. An important advantage of cold gases in such studies is the simplification due to the absence of relaxation mechanisms for spin currents apart from direct collisions between atoms of different spin, unlike, e.g., in a solid, where collisions with the ionic lattice can be important. In addition, the atomic interaction and initial temperature of the clouds are easily tunable parameters. Finally, as we shall see, very large spin polarizations can be easily created, leading to large spin currents.Here we study the collision of two clouds with opposite spin polarization following the recent experiments of Sommer et al. [7]. We confine ourselves to the semiclassical regime, using a Boltzmann equation simulation. In contrast, a recent theoretical study has instead used a hydrodynamic approach based on a many-body equation of state [9].One of the most striking experimental observations was the bouncing of the clouds off each other. Here we will demonstrate that this phenomenon can be understood purely in terms of semiclassical collisions, without recourse to, e.g., mean fields or other more complicated effects. For instance, our approach predicts that all quantities considered here depend only on the square of the scattering length and not on its sign. Also, as we will show, the bouncing oscillations can be understood as an example of a nonlinear coupling between * o.goulko@damtp.cam.ac.uk collective modes which, to the best of our knowledge, has not been studied in Fermi gases. , where ω z < ω x = ω y . We assume that the system is in the normal phase and that...

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Large amplitude spin waves in ultra-cold gases

Cited by 16 publications

References 43 publications

Universal Spin Transport and Quantum Bounds for Unitary Fermions

Universal Spin Transport and Quantum Bounds for Unitary Fermions

Relaxation Dynamics of an Isolated Large-Spin Fermi Gas Far from Equilibrium

Collision of two spin-polarized fermionic clouds

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