arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1711.03478cond-mat.quant-gascond-mat.otherquant-ph
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非平衡态强耦合玻色极化子的动力学RG方法

Strong coupling Bose polarons out of equilibrium: Dynamical RG approach

Fabian Grusdt, Kushal Seetharam, Yulia Shchadilova, Eugene Demler

摘要:

当一个可移动的杂质与周围的玻色子相互作用时,就会形成一个极化子。已经发展了许多方法来计算平衡情况下极化子的能量和有效质量如何被介质重整化。在这里,我们解决了少得多的研究非平衡制度,并调查如何极化子动态形成的时间。为此,我们开发了一个依赖于时间的重整化群方法,它允许计算系统的所有动力学性质,并考虑到量子涨落的影响,在极化子云。我们用这种方法计算了极化子在杂质-玻色子相互作用强度突然猝灭后的运动轨迹,揭示了杂质周围的极化子云是如何随时间形成的。这样的轨迹提供了关于极化子性质的额外信息,这些信息很难直接从使用超冷原子实验测量的光谱函数中提取。在强耦合下,我们的计算预测了杂质在中间时间由于量子涨落而波动的轨迹的出现。我们的方法适用于更广泛的一类非平衡问题。我们还应用它来计算谱函数,并找到与实验结果很好的一致性。在非常强的耦合,我们预测,量子涨落导致的外观的暗连续强烈抑制在低能量的光谱重量。虽然我们的计算开始于一个有效的Fröhlich哈密顿描述杂质在一个三维的玻色-爱因斯坦凝聚体,我们也计算的影响,额外的条款超出了Fröhlich范式的哈密顿。我们证明了这些附加项对费什巴赫共振吸引侧的主要作用是重整化有效Fröhlich模型的耦合强度。

英文摘要:

When a mobile impurity interacts with a surrounding bath of bosons, it forms a polaron. Numerous methods have been developed to calculate how the energy and the effective mass of the polaron are renormalized by the medium for equilibrium situations. Here we address the much less studied non-equilibrium regime and investigate how polarons form dynamically in time. To this end, we develop a time-dependent renormalization group approach which allows calculations of all dynamical properties of the system and takes into account the effects of quantum fluctuations in the polaron cloud. We apply this method to calculate trajectories of polarons following a sudden quench of the impurity-boson interaction strength, revealing how the polaronic cloud around the impurity forms in time. Such trajectories provide additional information about the polaron's properties which are challenging to extract directly from the spectral function measured experimentally using ultracold atoms. At strong couplings, our calculations predict the appearance of trajectories where the impurity wavers back at intermediate times as a result of quantum fluctuations. Our method is applicable to a broader class of non-equilibrium problems. We also apply it to calculate the spectral function and find good agreement with experimental results. At very strong couplings, we predict that quantum fluctuations lead to the appearance of a dark continuum with strongly suppressed spectral weight at low energies. While our calculations start from an effective Fröhlich Hamiltonian describing impurities in a three-dimensional Bose-Einstein condensate, we also calculate the effects of additional terms in the Hamiltonian beyond the Fröhlich paradigm. We demonstrate that the main effect of these additional terms on the attractive side of a Feshbach resonance is to renormalize the coupling strength of the effective Fröhlich model.

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