Unified theory of quantized electrons, phonons, and photons out of equilibrium: A simplifiedab initioapproach based on the generalized Baym-Kadanoff ansatz

Abstract

We present a full ab initio description of the coupled out-of-equilibrium dynamics of photons, phonons, and electrons. In the present approach, the quantized nature of the electromagnetic field as well as of the nuclear oscillations is fully taken into account. The result is a set of integrodifferential equations, written on the Keldysh contour, for the Green's functions of electrons, phonons, and photons where the different kinds of interactions are merged together. We then concentrate on the electronic dynamics in order to reduce the problem to a computationally feasible approach. By using the generalized Baym-Kadanoff ansatz and the completed collision approximation, we introduce a series of efficient but controllable approximations. In this way, we reduce all equations to a set of decoupled equations for the density matrix that describe all kinds of static and dynamical correlations. The final result is a coherent, general, and inclusive scheme to calculate several physical quantities: carrier dynamics, transient photoabsorption, and light emission, all of which include, at the same time, electron-electron, electron-phonon, and electron-photon interactions. We further discuss how all these observables can be easily calculated within the present scheme using a fully atomistic ab initio approach.

One-body reduced density-matrix functional theory in finite basis sets at elevated temperatures

“…The emergent hybrid light-matter states, so called polaritons, can lead to, e.g., a change of chemical reactions (Hutchison et al, 2012) or lead to exciton-polariton condensates (Byrnes et al, 2014). Since a detailed description of all constituents is necessary (Flick et al, 2017b,a), first-principles approaches extended to fermion-boson systems become important Tokatly, 2013;Ruggenthaler et al, 2014;Ruggenthaler, 2017;de Melo and Marini, 2016). The current work only deals with single-component systems.…”

Ab initiononrelativistic quantum electrodynamics: Bridging quantum chemistry and quantum optics from weak to strong coupling

“…In the photonic subsystem in the Born-Huang expansion this operatorvalued boost turns into a translation of the displacement coordinate for a given dipole moment R and therefore is equivalent toD † (q 0 ), which is just the tensor product of the individualD † (q 0 ) as defined in Eq. (22). Thus when we apply the coherent shift operator in the Born-Huang expansion we take the step back to the momentum form of the long-wavelength approximated minimal-coupling Hamiltonian.…”

Atoms and molecules in cavities, from weak to strong coupling in quantum-electrodynamics (QED) chemistry

“…This is the case, e.g., in so-called strong-coupling situations, which are nowadays of central interest in the fields of circuit quantum electrodynamics (circuit-QED) [20][21][22] or cavity-QED [23,24]. While the analysis of such experiments are routinely performed with the help of simplified (few-level) models that are able to capture the essential physics, for the (quantitative) prediction of properties of complex multiparticle systems coupled to photons, methods that can treat such coupled boson-fermion situations from first principles seem worthwhile [1,2,[25][26][27][28][29]. On the other hand, the strong coupling to photons can challenge our conventional understanding of electronic structures and allows to study the influence of the quantum nature of light on chemical processes.…”