Demagnetization dynamics of non-interacting trapped fermions

TL;DR

This paper analytically investigates the spin dynamics of non-interacting trapped fermions under magnetic field gradients, revealing how particle motion influences demagnetization and the effectiveness of spin-echo pulses, relevant for understanding spin transport in ultracold gases.

Contribution

It provides simple analytic expressions for spin observables in non-interacting fermions with magnetic gradients, highlighting the role of spin-motional coupling and limitations of spin-echo techniques.

Findings

Demagnetization decay can be faster than in strongly interacting regimes.

Particle motion limits spin-echo effectiveness in removing magnetic inhomogeneity.

Spin-echo pulses can increase magnetization decay at trapping period times.

Abstract

Motivated by several experimental efforts to understand spin diffusion and transport in ultracold fermionic gases, we study the spin dynamics of initially spin-polarized ensembles of harmonically trapped non-interacting spin-1/2 fermionic atoms, subjected to a magnetic field gradient. We obtain simple analytic expressions for spin observables in the presence of both constant and linear magnetic field gradients, with and without a spin-echo pulse, and at zero and finite temperatures. The analysis shows the relevance of spin-motional coupling in the non-interacting regime where the demagnetization decay rate at short times can be faster than the experimentally measured rates in the strongly interacting regime under similar trapping conditions. Our calculations also show that particle motion limits the ability of a spin-echo pulse to remove the effect of magnetic field inhomogeneity, and that a spin-echo pulse can instead lead to an increased decay of magnetization at times comparable to the trapping period.