Physical limits on electromagnetic response

TL;DR

This paper reviews recent advances in understanding the fundamental physical limits of electromagnetic responses in photonic devices, emphasizing a new theoretical framework that integrates optimization and conservation laws.

Contribution

It introduces an emerging theoretical framework that combines computational optimization with conservation laws to determine physical limits on optical responses.

Findings

Limits on thermal emission, scattering, and Purcell enhancement are characterized.

The framework captures all relevant wave effects in electromagnetic problems.

Future research directions include conceptual extensions and scalable numerical methods.

Abstract

Photonic devices play an increasingly important role in advancing physics and engineering, and while improvements in nanofabrication and computational methods have driven dramatic progress in expanding the range of achievable optical characteristics, they have also greatly increased design complexity. These developments have led to heightened relevance for the study of fundamental limits on optical response. Here, we review recent progress in our understanding of these limits with special focus on an emerging theoretical framework that combines computational optimization with conservation laws to yield physical limits capturing all relevant wave effects. Results pertaining to canonical electromagnetic problems such as thermal emission, scattering cross sections, Purcell enhancement, and power routing are presented. Finally, we identify areas for additional research, including conceptual extensions and efficient numerical schemes for handling large-scale problems.