Quantum-Electrodynamical Density-Functional Theory Exemplified by the Quantum Rabi Model

• URL: http://arxiv.org/abs/2411.15256v1
• Date: Fri, 22 Nov 2024 09:03:28 GMT
• Title: Quantum-Electrodynamical Density-Functional Theory Exemplified by the Quantum Rabi Model
• Authors: Vebjørn H. Bakkestuen, Vegard Falmår, Maryam Lotfigolian, Markus Penz, Michael Ruggenthaler, Andre Laestadius,
• Abstract summary: Key features of density-functional theory (DFT) within a minimal implementation of quantum electrodynamics are demonstrated. We derive a form for the adiabatic connection that is almost explicit in the density variables. This allows several key features of DFT to be studied without approximations.
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• Abstract: The key features of density-functional theory (DFT) within a minimal implementation of quantum electrodynamics are demonstrated, thus allowing to study elementary properties of quantum-electrodynamical density-functional theory (QEDFT). We primarily employ the quantum Rabi model, that describes a two-level system coupled to a single photon mode, and also discuss the Dicke model, where multiple two-level systems couple to the same photon mode. In these settings, the density variables of the system are the polarization and the displacement of the photon field. We give analytical expressions for the constrained-search functional and the exchange-correlation potential and compare to established results from QEDFT. We further derive a form for the adiabatic connection that is almost explicit in the density variables, up to only a non-explicit correlation term that gets bounded both analytically and numerically. This allows several key features of DFT to be studied without approximations.

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