We demonstrate that an ultracold many-body bosonic ensemble confined in a one-dimensional double-well potential can exhibit chaotic dynamics due to the presence of a single impurity. The nonequilibrium dynamics is triggered by a quench of the impurity-Bose interaction and is illustrated via the evolution of the population imbalance for the bosons between the two wells. While the increase of the postquench interaction strength always facilitates the irregular motion for the bosonic population imbalance, it becomes regular again when the impurity is initially populated in the highly excited states. Such an integrability to chaos (ITC) transition is fully captured by the transient dynamics of the corresponding linear entanglement entropy, whose infinite-time-averaged value additionally characterizes the edge of the chaos and implies the existence of an effective Bose-Bose attraction induced by the impurity. To elucidate the physical origin for the observed ITC transition, we perform a detailed spectral analysis for the mixture with respect to both the energy spectrum as well as the eigenstates. Specifically, two distinguished spectral behaviors upon a variation of the interspecies interaction strength are observed. While the avoided level crossings take place in the low-energy spectrum, the energy levels in the high-energy spectrum possess a bandlike structure and are equidistant within each band. This leads to a significant delocalization of the low-lying eigenvectors, which, in turn, accounts for the chaotic nature of the bosonic dynamics. By contrast, those highly excited states bear a high resemblance to the noninteracting integrable basis, which explains the recovery of the integrability for the bosonic species. Finally, we discuss the induced Bose-Bose attraction as well as its impact on the bosonic dynamics.

中文翻译：

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双阱中超冷玻色子系综的杂质诱导量子混沌

我们证明，由于单一杂质的存在，限制在一维双阱势中的超冷多体玻色子系综可以表现出混沌动力学。非平衡动力学由杂质-玻色相互作用的猝灭触发，并通过两口井之间玻色子种群不平衡的演变来说明。虽然淬火后相互作用强度的增加总是促进玻色子布居不平衡的不规则运动，但当杂质最初以高激发态填充时，它又变得规则了。这种对混沌 (ITC) 过渡的可积性完全被相应的线性纠缠熵的瞬态动力学所捕获，其无限时间平均值另外表征了混沌的边缘，并暗示存在由杂质引起的有效 Bose-Bose 引力。为了阐明观察到的 ITC 跃迁的物理起源，我们对混合物的能谱和本征态进行了详细的光谱分析。具体而言，观察到种间相互作用强度变化时的两种不同光谱行为。虽然避免的能级交叉发生在低能谱中，但高能谱中的能级具有带状结构并且在每个带内是等距的。这导致低位特征向量的显着离域，这反过来又解释了玻色动力学的混沌性质。相比之下，这些高度激发态与非相互作用的可积基高度相似，这解释了玻色物种可积性的恢复。最后，我们讨论了诱导的 Bose-Bose 引力及其对玻色动力学的影响。