Optical current, momentum and angular momentum in anisotropic materials exposed to detailed balance

Abstract

This work investigates the theory behind a thought experiment that intends to measure momentum and angular momentum of matter exposed to "isotropic radiative noise". Radiative momentum has been a controversial subject for decades. The momentum of isotropic noise is intuitively expected to be zero. We formulate the general features of the isotropic noise such as equipartition of energy and the vanishing of integrated Poynting vector. We demonstrate that in bi-anisotropic materials, a finite radiative momentum persists that performs work on the matter when its parameters change slowly. We find that Faraday rotation in the scattering of the radiative noise induces an angular momentum along the applied external magnetic field. Also, a Poynting vector starts circulating around the matter, raising the question whether it really describes the energy flow. These effects are small and hard to measure in any real experiment. Yet, they are surprising predictions of the classical, macroscopic Maxwell equations, and make contact with the outcome of recent QED calculations done for the quantum vacuum.

Longitudinal Angular Momentum in Magneto-Mie Scattering: Quantum Vacuum Correction to the Einstein-De Haas effect

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Stirring the quantum vacuum: Angular Casimir momentum of a Landau charge

“…In a pioneering work [3] Feigel predicted "Casimir" momentum in bi-anisotropic materials. Although the Poynting vector of the quantum vacuum still vanishes [4], a momentum density emerges that suffers from a divergence at high energies. Relativistic photons were already known to be relevant for the Lamb shift [1], in contrast to Casimir-Polder forces [2], caused by lowenergy vacuum photons.…”