Large amplitude spin waves in ultra-cold gases

Abstract

We discuss the theory of spin waves in non-degenerate ultra-cold gases, and compare various methods which can be used to obtain appropriate kinetic equations. We then study non-hydrodynamic situations, where the amplitude of spin waves is sufficiently large to bring the system far from local equilibrium. In the first part of the article, we compare two general methods which can be used to derive a kinetic equation for a dilute gas of atoms (bosons or fermions) with two internal states (treated as a pseudo-spin 1/2). The collisional methods are in the spirit of Boltzmann's original derivation of his kinetic equation where, at each point of space, the effects of all sorts of possible binary collisions are added. We discuss two different versions of collisional methods, the Yvon-Snider approach and the S matrix approach. The second method uses the notion of mean field, which modifies the drift term of the kinetic equation, in the line of the Landau theory of transport in quantum liquids. For a dilute cold gas, it turns out that all these derivations lead to the same drift terms in the transport equation, but differ in the precise expression of the collision integral and in higher order gradient terms. In the second part of the article, the kinetic equation is applied to spin waves in trapped ultra-cold gases. Numerical simulations are used to illustrate the strongly non-hydrodynamic character of the spin waves recently observed with trapped Rb87 atoms. The decay of the phenomenon, which takes place when the system relaxes back towards equilibrium, is also discussed, with a short comment on decoherence.

arXiv commentTo appear in Eur. Phys. J. D

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• Spatial resolution of spin waves in an ultra-cold gas
• Internal state conversion in ultracold gases
• Internal waves and synchronized precession in a cold vapor
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• Linear spin waves in a trapped Bose gas
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• The Interference Term in the Wigner Distribution Function and the Aharonov-Bohm Effect
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Cited by in corpus (14)

• Spectroscopic insensitivity to cold collisions in a two-state mixture of fermions
• Cumulative identical spin rotation effects in collisionless trapped atomic gases
• Normal-superfluid interaction dynamics in a spinor Bose gas
• Universal Spin Transport and Quantum Bounds for Unitary Fermions
• Collision of two spin polarized fermionic clouds
• Engineering spin waves in a high-spin ultracold Fermi gas
• Spin segregation via dynamically induced long-range interaction in a system of ultracold fermions
• Relaxation dynamics of an isolated large-spin Fermi gas far from equilibrium
• Nonlinear spin diffusion and spin rotation in a trapped Fermi gas
• Spin Diffusion in Trapped Gases: Anisotropy in Dipole and Quadrupole Modes
• Optical excitation of nonlinear spin waves
• Localized collapse and revival of coherence in an ultracold Bose gas
• Anisotropic Spin Diffusion in Trapped Boltzmann Gases
• Stable spin domains in a non-degenerate ultra-cold gas