Making ab initio QED functional(s): Nonperturbative and photon-free effective frameworks for strong light-matter coupling
Artikel i vetenskaplig tidskrift, 2021

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.


cavity quantum

photon-free QED

quantum-electrodynamical density-functional theory (QEDFT)

QEDFT functionals

strong light-matter coupling


Christian Schäfer


Universität Hamburg

Chalmers, Mikroteknologi och nanovetenskap, Tillämpad kvantfysik

Florian Buchholz


Markus Penz

University of Innsbruck

Michael Ruggenthaler

Universität Hamburg


Angel Rubio


Universität Hamburg

Proceedings of the National Academy of Sciences of the United States of America

0027-8424 (ISSN) 1091-6490 (eISSN)

Vol. 118 41 e2110464118

Kvantplasmonik – en teknologi för foton-fotonväxelverkan på kvantnivå vid rumstemperatur

Vetenskapsrådet (VR) (2016-06059), 2017-01-01 -- 2022-12-31.



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