Laboratoire Pierre Aigrain, Ecole Normale Supérieure-PSL Research University, CNRS, Université Pierre et Marie Curie-Sorbonne Universités, Université Paris Diderot-Sorbonne Paris Cité, 24 rue Lhomond, 75231 Paris Cedex 05, France.
JILA and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.
Nature. 2017 May 4;545(7652):71-74. doi: 10.1038/nature21704. Epub 2017 Apr 12.
The ability to control electronic states at the nanoscale has contributed to our modern understanding of condensed matter. In particular, quantum dot circuits represent model systems for the study of strong electronic correlations, epitomized by the Kondo effect. We use circuit quantum electrodynamics architectures to study the internal degrees of freedom of this many-body phenomenon. Specifically, we couple a quantum dot to a high-quality-factor microwave cavity to measure with exceptional sensitivity the dot's electronic compressibility, that is, its ability to accommodate charges. Because electronic compressibility corresponds solely to the charge response of the electronic system, it is not equivalent to the conductance, which generally involves other degrees of freedom such as spin. Here, by performing dual conductance and compressibility measurements in the Kondo regime, we uncover directly the charge dynamics of this peculiar mechanism of electron transfer. The Kondo resonance, visible in transport measurements, is found to be 'transparent' to microwave photons trapped in the high-quality cavity, thereby revealing that (in such a many-body resonance) finite conduction is achieved from a charge frozen by Coulomb interaction. This freezing of charge dynamics is in contrast to the physics of a free electron gas. We anticipate that the tools of cavity quantum electrodynamics could be used in other types of mesoscopic circuits with many-body correlations, providing a model system in which to perform quantum simulation of fermion-boson problems.
控制纳米尺度电子态的能力促进了我们对凝聚态物质的现代理解。特别是，量子点电路是研究强电子相关的模型体系，以近藤效应为代表。我们使用电路量子电动力学架构来研究这种多体现象的内部自由度。具体来说，我们将一个量子点耦合到一个高品质因数的微波腔中，以极高的灵敏度测量量子点的电子压缩性，即其容纳电荷的能力。因为电子压缩性仅对应于电子系统的电荷响应，所以它与电导不同，电导通常涉及其他自由度，如自旋。在这里，我们在近藤区进行了双重电导和压缩性测量，直接揭示了这种特殊电子转移机制的电荷动力学。在输运测量中可见的近藤共振对被困在高品质腔中的微波光子是“透明的”，从而表明（在这种多体共振中）通过库仑相互作用冻结的电荷可以实现有限的传导。这种电荷动力学的冻结与自由电子气的物理性质形成对比。我们预计，腔量子电动力学的工具可以用于具有多体相关性的其他类型的介观电路，提供一个模型系统，在其中可以对费米子-玻色子问题进行量子模拟。
