APL Quantum (Jun 2024)
QED in space–time varying materials
Abstract
Space–time variation spoils frequency conservation and brings negative frequencies into the picture. In addition, the quantum nature of light comes to the fore in a manner not evident in static systems. Here, we explore the quantum structure of these systems; propose a Hamiltonian; show that, in the Heisenberg picture, quantum field operators evolve according to classical equations; and discuss the uniquely quantum phenomenon of photon-pair creation.