Numerical Framework for Modeling Quantum Electromagnetic Systems Involving Finite-Sized Lossy Dielectric Objects in Free Space

TL;DR

This paper introduces a numerical framework using finite-element methods to model quantum electromagnetic fields around finite lossy dielectric objects, validating the modified Langevin noise formalism and enabling practical calculations of atomic emission rates.

Contribution

It develops a novel computational approach to implement the modified Langevin noise formalism for finite-sized lossy dielectrics, bridging theory and practical numerical analysis.

Findings

Validated the modified Langevin noise formalism numerically

Successfully calculated the Purcell factor in lossy environments

Confirmed the Green's function expression for spontaneous emission rate

Abstract

The modified Langevin noise formalism has been proposed for the correct charaterization of quantum electromagnetic fields in the presence of finite-sized lossy dielectric objects in free space. The main modification to the original one (also known as the Green's function approach available only for bulk inhomogeneous lossy dielectric medium) was to add fluctuating sources in reaction to the radiation loss. Consequently, a resulting electric field operator is now determined by (i) boundary-assisted and (ii) medium-assisted fields on an equal footing, which are fluctuating sources due to radiation and medium losses, respectively. However, due to the lengthy mathematical manipulation and complicated concepts, the validity of the modified Langevin noise formalism has not been clearly checked yet. In this work, we propose and develop a novel numerical framework for the modified Langevin noise formalism by exploiting computational electromagnetic methods (CEM). Specifically, we utilize the finite-element method to numerically solve plane-wave-scattering and point-source-radiation problems whose solutions are boundary-assisted and medium-assisted fields, respectively. Based on the developed numerical framework, we calculate the Purcell factor of a two-level atom inside or outside a lossy dielectric slab. It is numerically proved, for the first time, that one can retrieve the conventional expression of the spontaneous emission rate, viz., the imaginary part of the Green's function. The proposed numerical framework is particularly useful for estimating the dynamics of multi-level atoms near practical plasmonic structures or metasurfaces.