Metastable hard-axis polar state of a spinor Bose-Einstein condensate under a magnetic field gradient

Abstract

We investigate the stability of a hard-axis polar state in a spin-1 antiferromagnetic Bose-Einstein condensate under a magnetic field gradient, where the easy-plane spin anisotropy is controlled by a negative quadratic Zeeman energy $q<0$. In a uniform magnetic field, the axial polar state is dynamically unstable and relaxes into the planar polar ground state. However, under a field gradient $B^{\prime }$, the excited spin state becomes metastable down to a certain threshold $q_{th}$ and as $q$ decreases below $q_{th}$, its intrinsic dynamical instability is rapidly recalled. The incipient spin excitations in the relaxation dynamics appear with stripe structures, indicating the rotational symmetry breaking by the field gradient. We measure the dependences of $q_{th}$ on $B^{\prime }$ and the sample size, and we find that $q_{th}$ is highly sensitive to the field gradient in the vicinity of $B^{\prime }=0$, exhibiting power-law behavior of $|q_{th}|\propto B^{\prime \alpha }$ with $\alpha \sim 0.5$. Our results demonstrate the significance of the field gradient effect in the quantum critical dynamics of spinor condensates.

arXiv comment8 pages, 7 figures

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• Metastable spin-phase diagrams in antiferromagnetic Bose-Einstein condensates
• Thermal effects on the spin domain phases of high spin-f Bose-Einstein condensates with rotational symmetries
• Generation of squeezed optical states via stored classical pulses in a Bose gas