The Kondo effect in ultracold atoms

超冷原子中的近藤效应

• 批准号: 377616843
• 负责人: Professor Dr. Fred Jendrzejewski
• 金额: --
• 依托单位: Kirchhoff-Institut für Physik
• 依托单位国家: 德国
• 项目类别: Independent Junior Research Groups
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/377616843?language=en
• 关键词: Kondo; effect; ultracold; atoms

The simplicity of impurity models, combined with the often fundamental importance of the impurity on the emergent properties of the system, makes them a fruitful starting point for studies of open questions at the forefront of physics. We propose to implement the Kondo impurity model with ultracold atomic mixtures as experimental benchmark for open questions such as dynamical properties of highly correlated systems as well as the emergence of non-Fermi liquids. The 'single-channel' Kondo model describes the antiferromagnetic coupling of a localized impurity to a sea of spin-1/2 Fermions. The impurity can be treated perturbatively at high temperatures, but for low temperatures the impurity binds a Fermion into a singlet. In the ground state, the impurity is therefore entirely screened from the other Fermions by the Kondo screening cloud. The transition in the region of the Kondo temperature cannot be described by perturbative approaches and is a standard benchmark problem for non-perturbative methods. The situation changes dramatically in the 'multi-channel' Kondo model, where the impurity is coupled to more than one channel of spin-1/2 Fermions. In this case, the ground state is the superposition of spin singlets, each formed by the impurity and a Fermion from one of the channels. This degeneracy leads to strong quantum correlations between the channels, competing for the singlet formation with the impurity. These quantum correlations can even manifest themselves macroscopically in the formation of a non-Fermi liquid state. The excitations are losing their fermionic character in such a state. The emergence of these new quasi-particles and the prediction of their properties remains an open problem of fundamental physics. The goal of this proposal is to establish atomic mixtures as a new platform for investigating the Kondo model. The experimental parameters of these extremely clean and tunable systems enjoy a high versatility and they are now established as a benchmarking platform for a variety of model systems. Despite this attractiveness, no experimental results have been reported so far on the Kondo model. The multi-channel Fermi sea will be realized by a large cloud of Fermions with large spin. They will be trapped in a weak optical trap such that the spin is free to flip. The spin impurity will be realized by a few bosonic atoms that are localized in the ground states of a deep optical trap, such that its motion is frozen out. The exchange interaction will arise due to spin-changing collisions between the Bosons and the Fermions. We expect the interaction strength to be sufficiently high to obtain a Kondo temperature in the order of the Fermi temperature, which is experimentally accessible. The Kondo effect will be observed through local spin correlations between the Bosons and Fermions. We will detect non-Fermi liquid behavior through the non-fermionic propagation of correlations after a quench.

杂质模型的简单性，再加上杂质对系统涌现性质的重要作用，使它们成为研究物理学前沿开放问题的一个富有成效的起点。我们建议用超冷原子混合物实现Kondo杂质模型作为实验基准，以解决诸如高度关联系统的动力学性质以及非费米液体的出现等公开问题。“单通道”近藤模型描述了局域杂质与自旋1/2费米子海的反铁磁耦合。在高温下，杂质可以微扰处理，但在低温下，杂质会将费米子束缚成单重态。因此，在基态时，近藤屏蔽云将杂质与其他费米子完全隔绝。近藤温度区域的转变不能用微扰方法来描述，它是非微扰方法的标准基准问题。在“多通道”近藤模型中，情况发生了很大的变化，在该模型中，杂质耦合到多个自旋1/2费米子通道。在这种情况下，基态是自旋单态的叠加，每个自旋单态都是由杂质和来自其中一个通道的费米子形成的。这种简并导致了通道之间的强量子关联，与杂质竞争单重态的形成。这些量子关联甚至可以在宏观上表现为非费米液态的形成。在这样的状态下，激发子正在失去费米子性质。这些新的准粒子的出现及其性质的预测仍然是基础物理学的一个悬而未决的问题。这项提议的目标是建立原子混合物，作为研究近藤模型的新平台。这些极其清洁和可调的系统的实验参数具有很高的通用性，现在它们被建立为各种模型系统的基准平台。尽管有这种吸引力，但到目前为止，还没有关于近藤模型的实验结果的报道。多道费米海将由一大团自旋较大的费米子云实现。它们将被困在一个微弱的光学陷阱中，这样自旋就可以自由翻转。自旋杂质将由几个玻色原子实现，这些原子定域在一个深光学陷阱的基态中，从而使其运动被冻结。由于玻色子和费米子之间的自旋变化碰撞，将产生交换相互作用。我们希望相互作用强度足够高，以获得费米温度量级的近藤温度，这在实验上是可以获得的。近藤效应将通过玻色子和费米子之间的局域自旋关联来观察。我们将通过失超后关联的非费米传播来检测非费米液体行为。