Fluctuational Quantum Electrodynamics Accounts for Lossy Media

Jaime E. Sustaeta-Osuna, Thomas F. Allard, Francisco J. García-Vidal, and Paloma A. Huidobro of Universidad Autónoma de Madrid have developed a new framework for understanding how light and matter interact in materials with changing properties. Their work details a generalized Fermi Golden Rule specifically designed for media that evolve over time, moving beyond calculations that previously treated the temporal modulation as a perturbation. The researchers modeled two distinct geometries, a periodically driven polar insulator and a plasmonic medium, as examples after developing the theory. Analysis of the polar insulator revealed a strong enhancement of light-matter interactions at the Floquet sidebands of the surface phonon frequency. This approach allows for analysis of thermal radiation and electromagnetic field correlations in these dynamic systems, exceeding the limitations of standard perturbation theory.

Fluctuational Quantum Electrodynamics for Dispersive Time-Varying Media

A complete, consistent quantization of the electromagnetic field within time-modulated materials has been developed, addressing a long-standing limitation in the field of temporal optics. Researchers at Universidad Autónoma de Madrid have built upon previous works that treated temporal modulation as a perturbation, instead developing a framework that accounts for dispersive and lossy behavior without relying on perturbative methods. Using this theory, they derive a generalized Fermi Golden Rule for time-varying media, which allows us to define the local density of states for these time-dependent systems.

The fast modulation regime of the plasmonic medium exhibits coupling to negative frequency replicas, potentially leading to gain and the dynamical Casimir effect, where photons are generated from the quantum vacuum through the energy provided by the temporal modulation. The team studies the correlation functions of the electromagnetic field, showing how the time modulation enables the creation of entangled polariton pairs exhibiting non-local spatial correlations. The relative change in the refractive index induced by the time modulation can be significant, rendering perturbative approaches ineffective.

Researchers at Universidad Autónoma de Madrid are refining models of how light interacts with materials undergoing change, with implications for advanced optical devices and metamaterials. Jaime E. Sustaeta-Osuna and his colleagues derived a Fermi Golden Rule which allows for the definition of a local density of states in these time-dependent systems, a crucial step toward predicting light-matter interactions in dynamic environments. These sidebands represent specific frequencies at the Floquet sidebands of the surface phonon frequency, and the enhancement suggests a boosted interaction at those particular wavelengths.

The ability to manipulate light-matter interactions with increased control is edging closer to reality, thanks to new theoretical work detailing how rapidly changing material properties can generate gain and even create photons from empty space. This dynamical Casimir effect, a purely quantum phenomenon, involves the creation of entangled photons from the quantum vacuum through the energy provided by the temporal modulation. “Crucially, our theory accounts for both dispersion and losses in the time modulation and goes beyond perturbative approaches,” enabling a more accurate and comprehensive understanding of these complex systems.

Thermal Radiation Analysis Beyond Perturbation Theory

Beyond established models of light-matter interaction, a new theoretical framework developed by Jaime E. Sustaeta-Osuna, Thomas F. Allard, Francisco J. García-Vidal, and Paloma A. Huidobro offers a more complete picture of how materials respond to fluctuating electromagnetic fields, particularly when those materials are undergoing rapid changes. This work accounts for the dispersive and lossy nature of the temporal modulation, treating it in an exact manner without relying on perturbative methods. They derived a generalized Fermi Golden Rule for time-varying media, which allows us to define the local density of states in these time-dependent systems.

A newly developed theoretical framework directly addresses light-matter interactions in dynamically changing materials, accounting for dispersion and loss without relying on perturbative methods. Researchers Jaime E. Sustaeta-Osuna, Thomas F. Allard, Francisco J. García-Vidal, and Paloma A. Huidobro established a foundation for understanding and harnessing quantum effects in dynamically modulated materials, potentially impacting fields from metamaterials to advanced optical devices.

Limitations of Existing Approaches to Time-Varying Media

Existing theoretical treatments of light-matter interactions in dynamically modulated materials often rely on approximations that limit their accuracy and scope. Many earlier works treated the temporal modulation as a perturbation, useful for qualitative insights but incapable of quantitative predictions beyond weak modulation strengths, or in regimes where non-perturbative effects dominate. This approach struggles to accurately model the strong modulation scenarios increasingly accessible through experimental advances in metamaterials and near-zero index materials. Other theoretical efforts, while avoiding perturbation theory, assumed lossless or dispersionless modulation, leading to inaccuracies in the predicted linear response and violating fundamental relationships like the Kramers-Kronig relations. These limitations stem from a need for a comprehensive theory that simultaneously addresses both the dispersive and dissipative characteristics of time-varying media. Researchers have also pursued microscopic theories, but these are typically system-dependent, hindering the development of a unified framework applicable to diverse materials.

Contemporary experimental platforms, including plasmonic metamaterials operating in the terahertz range and transmission line metamaterials in the microwave spectrum, inherently exhibit dispersion and dissipation, further exposing the inadequacies of simplified models. To overcome these challenges, a new formalism has been developed, focusing on fluctuational quantum electrodynamics. The resulting framework is inherently quantum mechanical.