文章基本信息

标题：Making ab initio QED functional(s): Nonperturbative and photon-free effective frameworks for strong light–matter coupling
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作者：Christian Schäfer ; Florian Buchholz ; Markus Penz 等
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：2021
卷号：118
期号：41
DOI：10.1073/pnas.2110464118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance Strong interaction between light and matter recently attracted enormous interest after seminal work highlighted how materials and chemical reactions can be effectively controlled with cavities, suggesting new quantum technological applications and alternative paths to catalysis. Combining the quantized nature of light and matter is, however, a nontrivial task due to the overwhelming complexity of the combined system. We first motivate a nonperturbative photon-free reformulation of quantum electrodynamics (QED) that recovers, even in its simplest form, the correct physical limits of the original QED problem, providing us with an efficient framework for further developments. By combination with density-functional theory, we obtain the first nonperturbative local density–type functional that describes the quantized interaction between light and matter while remaining computationally feasible. Strong light–matter coupling provides a promising path for the control of quantum matter where the latter is routinely described from first principles. However, combining the quantized nature of light with this ab initio tool set is challenging and merely developing as the coupled light–matter Hilbert space is conceptually different and computational cost quickly becomes overwhelming. In this work, we provide a nonperturbative photon-free formulation of quantum electrodynamics (QED) in the long-wavelength limit, which is formulated solely on the matter Hilbert space and can serve as an accurate starting point for such ab initio methods. The present formulation is an extension of quantum mechanics that recovers the exact results of QED for the zero- and infinite-coupling limit and the infinite-frequency as well as the homogeneous limit, and we can constructively increase its accuracy. We show how this formulation can be used to devise approximations for quantum-electrodynamical density-functional theory (QEDFT), which in turn also allows us to extend the ansatz to the full minimal-coupling problem and to nonadiabatic situations. Finally, we provide a simple local density–type functional that takes the strong coupling to the transverse photon degrees of freedom into account and includes the correct frequency and polarization dependence. This QEDFT functional accounts for the quantized nature of light while remaining computationally simple enough to allow its application to a large range of systems. All approximations allow the seamless application to periodic systems.
关键词：enquantum-electrodynamical density-functional theory (QEDFT);cavity quantum electrodynamics;strong light–matter coupling;photon-free QED;QEDFT functionals