期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：50
页码：15285-15290
DOI：10.1073/pnas.1518224112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceDensity-functional theory (DFT) is a well-established method to study many-electron systems. Over the past decades advanced algorithms have been designed that allow even large systems to be solved computationally very efficiently. Only recently, DFT has been generalized to correctly incorporate the quantum nature of light, which becomes important, e.g., in cavity quantum electrodynamics (QED). In general, the accuracy in density-functional theory depends crucially on the capability to construct good approximations that reflect the features of the exact effective potential for the Kohn-Sham system. In this work, we introduce a fixed-point scheme to construct these exact effective potentials for a cavity QED system and demonstrate their features for the ground-state and time-dependent situations. The density-functional approach to quantum electrodynamics extends traditional density-functional theory and opens the possibility to describe electron-photon interactions in terms of effective Kohn-Sham potentials. In this work, we numerically construct the exact electron-photon Kohn-Sham potentials for a prototype system that consists of a trapped electron coupled to a quantized electromagnetic mode in an optical high-Q cavity. Although the effective current that acts on the photons is known explicitly, the exact effective potential that describes the forces exerted by the photons on the electrons is obtained from a fixed-point inversion scheme. This procedure allows us to uncover important beyond-mean-field features of the effective potential that mark the breakdown of classical light-matter interactions. We observe peak and step structures in the effective potentials, which can be attributed solely to the quantum nature of light; i.e., they are real-space signatures of the photons. Our findings show how the ubiquitous dipole interaction with a classical electromagnetic field has to be modified in real space to take the quantum nature of the electromagnetic field fully into account.
关键词：time-dependent density functional theory ; strong light matter interaction ; quantum electrodynamics ; photon matter correlations ; quantum electrodynamical density functional theory
