Giant Spin Oscillations in an Ultracold Fermi Sea

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Science  10 Jan 2014:
Vol. 343, Issue 6167, pp. 157-160
DOI: 10.1126/science.1244059

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Collective Coherent Spin Dynamics

Ultracold gases have shown considerable promise for the quantum simulation of more complicated systems, such as correlated electrons in solids. Usually, researchers use two hyperfine states of the atoms to correspond to the spin up and down states of the electrons; however, these gases typically have a much richer internal state structure. Krauser et al. (p. 157) observed the coherent behavior of a gas of potassium-40 atoms that had 10 accessible internal spin states and that evolved through collisions. The spin state of the system oscillated as a whole, a surprising finding given that the atoms are fermions.


Collective behavior in many-body systems is the origin of many fascinating phenomena in nature, ranging from the formation of clouds to magnetic properties of solids. We report on the observation of collective spin dynamics in an ultracold Fermi sea with large spin. As a key result, we observed long-lived and large-amplitude coherent spin oscillations driven by local spin interactions. At ultralow temperatures, Pauli blocking stabilizes the collective behavior, and the Fermi sea behaves as a single entity in spin space. With increasing temperature, we observed a stronger damping associated with particle-hole excitations. Unexpectedly, we found a high-density regime where excited spin configurations are collisionally stabilized. Our results reveal the intriguing interplay between microscopic processes either stimulating or suppressing collective effects in a fermionic many-body system.

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