Superluminality and spatial field confinement in optical tunneling

Abstract

The fact that the source domain of an electromagnetic field emitted from an electric-dipole active atom extends over the entire near-field zone of the particle is used to argue that superluminality always appears in optical tunneling processes. The superluminal response does not violate the Einstein causality because it originates solely in our inability to confine photons completely in space and thus not in field propagation (with the vacuum speed of light). The time delay in the tunneling process is shown to depend in a crucial manner on the detection process. Superluminality originating in lack of spatial field confinement in an experiment may look as if photon propagation with a speed larger than c 0 has occurred. We emphasize this by presenting for a single point dipole and an array of dipoles calculations of the apparent velocity of field propagation, and show that this velocity depends on the detector threshold level and the source detector distance.