Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture
Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture
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DOI：
10.1038/nature11065
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发表时间：
2012-05-31
期刊：
影响因子：
64.8
通讯作者：
Grimm, R.
中科院分区：
文献类型：
--
作者：
Kohstall, C.;Zaccanti, M.;Grimm, R.
具有可调相互作用的超冷费米气体为探索强相互作用量子系统的多体物理提供了一个试验平台（1-4）。在过去的十年里，实验研究了许多有趣的现象，基态性质的精确测量为理论描述的发展提供了基准。具有强排斥相互作用的费米气体中的亚稳态（5-11）代表了一个令人兴奋的发展领域。实现这样的系统是具有挑战性的，因为原子量子气体中的强排斥相互作用意味着存在弱束缚分子态，这使得系统本质上不稳定。在这里，我们使用射频光谱测量费米K-40杂质共振相互作用的费米海的Li-6原子的完整的激发光谱。特别是，我们表明，一个定义良好的准粒子存在强排斥相互作用。我们测量了这种“排斥极化子”的能量和寿命（9，12，13），并通过测量准粒子留数来探测它的相干性质。结果很好地描述了一个理论的方法，考虑到在我们的系统中的相互作用的有限的有效范围。我们发现，当有效范围是粒子间距的顺序，有一个大幅度增加的准粒子的寿命。这种长寿命的亚稳态多体状态的存在，为在超冷的、相互排斥的费米气体中创造奇异的量子相提供了有趣的前景。
Ultracold Fermi gases with tunable interactions provide a test bed for exploring the many-body physics of strongly interacting quantum systems(1-4). Over the past decade, experiments have investigated many intriguing phenomena, and precise measurements of ground-state properties have provided benchmarks for the development of theoretical descriptions. Metastable states in Fermi gases with strong repulsive interactions(5-11) represent an exciting area of development. The realization of such systems is challenging, because a strong repulsive interaction in an atomic quantum gas implies the existence of a weakly bound molecular state, which makes the system intrinsically unstable against decay. Here we use radio-frequency spectroscopy to measure the complete excitation spectrum of fermionic K-40 impurities resonantly interacting with a Fermi sea of Li-6 atoms. In particular, we show that a well-defined quasiparticle exists for strongly repulsive interactions. We measure the energy and the lifetime of this 'repulsive polaron'(9,12,13), and probe its coherence properties by measuring the quasiparticle residue. The results are well described by a theoretical approach that takes into account the finite effective range of the interaction in our system. We find that when the effective range is of the order of the interparticle spacing, there is a substantial increase in the lifetime of the quasiparticles. The existence of such a long-lived, metastable many-body state offers intriguing prospects for the creation of exotic quantum phases in ultracold, repulsively interacting Fermi gases.