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Journal of Physics Conference Series

Ferromagnetism of spinor atomic condensates in the double well

Chengjun Tao, Qiang Gu

Published Dec 17, 2012• 1 citation
Publisher

Abstract

We show that the ferromagnetic and antiferromagnetic spinor condensates display distinct dynamical behaviors in double well. For the ferromagnetic case, strong symmetry-breaking dynamics can be induced by a small initial distortion. Contrarily, the σ = ±1 components tend to be well mixed in the antiferromagnetic condensate. The tunneling coupling plays an important role in distinguishing ferromagnetism and antiferromagnetism.

DOI
10.1088/1742-6596/400/1/012073

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The dynamics of F =1 spinor condensates initially prepared in a double-well potential is studied in the mean-field approach. It is shown that a small seed of m =0 atoms on a system with initially well-separated m =1 and m =-1 condensates has a dramatic effect on their mixing dynamics, acting as an effective barrier for a remarkably long time. We show that this effect is due to the spinor character of the system, and provides an observable example of the interplay between the internal spin dynamics and the macroscopic evolution of the magnetization in a spinor Bose-Einstein condensate.
We consider a spin-1/21/21/2 Bose-Einstein condensate initially prepared in a single-spin projection. The two channels of dynamical excitations existing in such a system (density and spin waves) are discussed and we show how pure spin waves can be excited in the presence of local magnetic defects. We analyze the role played by spin excitations on the Landau superfluidity criterion and demonstrate the absence of absolute superfluidity for the antiferromagnetic condensate. In the ferromagnetic case, we identify two critical velocities for the breakdown of superfluidity.
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We discuss the quantum phases and their diffusion dynamics in a spinor-1 atomic Bose-Einstein condensate. For ferromagnetic interactions, we obtain the exact ground-state distribution of the phases associated with the total atom number (N),(N),(N), the total magnetization (M),(\mathcal{M}),(M), and the alignment (or hypercharge) (Y) of the system. The mean-field ground state is stable against fluctuations of atom numbers in each of the spin components, and the phases associated with the order parameter for each spin components diffuse while dynamically recovering the two broken continuous symmetries [U(1) and SO(2)] when N and M\mathcal{M}M are conserved, as in current experiments. We discuss the implications to the quantum dynamics due to an external (homogeneous) magnetic field. We also comment on the case of a spinor-1 condensate with antiferromagnetic interactions.