Transverse Demagnetization Dynamics of a Unitary Fermi Gas
Transverse Demagnetization Dynamics of a Unitary Fermi Gas
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DOI：
10.1126/science.1247425
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发表时间：
2013-10
期刊：
影响因子：
56.9
通讯作者：
A. B. Bardon;S. Beattie;C. Luciuk;W. Cairncross;Dan Fine;N. Cheng;G. Edge;E. Taylor;Shi-Xun Zhang;S. Trotzky;J. Thywissen
中科院分区：
文献类型：
--
作者：
A. B. Bardon;S. Beattie;C. Luciuk;W. Cairncross;Dan Fine;N. Cheng;G. Edge;E. Taylor;Shi-Xun Zhang;S. Trotzky;J. Thywissen
在所谓的幺正态中解开自旋螺旋超冷费米气体--原子之间的发散相互作用使它们的热力学具有普适性--是一系列强相互作用物质系统的极好测试平台。在这个政权的运输特性是特别有趣的，和二维和三维的运输系数之间的差异已被观察到。Bardon等人（第722页）研究了三维费米气体的退磁动力学。气体最初是沿沿着一个方向极化的，并且没有相互作用。然后施加磁场梯度，形成自旋螺旋;当气体从这种状态松弛时，作者提取了扩散系数，并观察到原子之间相互作用的积累。在磁场梯度中的钾原子气体中观察到自旋取向的扩散。理解强相互作用费米子的量子动力学是一个与不同形式物质相关的问题，包括高温超导体，中子星和夸克胶子等离子体。在强相互作用的幺正极限下，冷原子气体提供了一个吸引人的基准。本文研究了非均匀磁场中横向磁化幺正费米气体的动力学行为。我们观察到的气体，扩散自旋输运所造成的退磁。在低温下，扩散常数会饱和到量子力学的下限λ max/m，其中m是粒子质量。通过测量Tan的接触参数，观察到了对相关的发展，表明了最初不相互作用的气体向单一自旋混合物的转变。
Untwisting the Spin Spiral Ultracold Fermi gases in the so-called unitary regime—where the diverging interactions between atoms make their thermodynamics universal—are an excellent test bed for an array of strongly interacting matter systems. The transport characteristics in this regime are particularly intriguing, and a discrepancy between two- and three-dimensional transport coefficients has been observed. Bardon et al. (p. 722) studied the demagnetization dynamics of a three-dimensional Fermi gas. The gas was initially polarized along a single direction and was noninteracting. An applied magnetic field gradient then caused a spin spiral to form; as the gas relaxed from this state, the authors extracted the diffusion coefficient and observed the buildup of interactions between the atoms. The diffusion of spin orientation is observed in a gas of potassium atoms in a magnetic field gradient. Understanding the quantum dynamics of strongly interacting fermions is a problem relevant to diverse forms of matter, including high-temperature superconductors, neutron stars, and quark-gluon plasma. An appealing benchmark is offered by cold atomic gases in the unitary limit of strong interactions. Here, we study the dynamics of a transversely magnetized unitary Fermi gas in an inhomogeneous magnetic field. We observe the demagnetization of the gas, caused by diffusive spin transport. At low temperatures, the diffusion constant saturates to the conjectured quantum-mechanical lower bound ≃ℏ/m, where m is the particle mass. The development of pair correlations, indicating the transformation of the initially noninteracting gas toward a unitary spin mixture, is observed by measuring Tan’s contact parameter.