Self-organization in driven dissipative systems is an active field of research with implications in physics, chemistry, and biology. When applying a red-detuned retroreflected laser beam to a large cloud of cold atoms, we observe the spontaneous formation of 2D structures in the transverse plane corresponding to high contrast spatial modulations of both light field and atomic spins. By applying a weak magnetic field, we explore the rich resulting phase space and identify specific phases associated with both dipolar and quadrupolar terms of the atomic magnetic moment. In particular, we demonstrate spontaneous structures in optically induced ground state coherences representing magnetic quadrupoles. Our results illustrate the wealth of behavior exhibited by laser-driven atomic media with complex level structure under optical feedback.

中文翻译：

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光原子自旋结构在冷原子中的磁相图

驱动耗散系统中的自组织是一个活跃的研究领域，具有物理，化学和生物学的意义。当将红色失谐的回射激光束应用于大量冷原子云时，我们观察到横向平面中自发形成2D结构，这与光场和原子自旋的高对比度空间调制相对应。通过施加弱磁场，我们探索了丰富的相空间，并确定了与原子磁矩的偶极和四极项相关的特定相。特别是，我们展示了代表磁性四极子的光诱导基态相干中的自发结构。我们的结果说明了在光反馈下具有复杂能级结构的激光驱动原子介质表现出的丰富行为。