Comment on: Direct space-time observation of pulse tunneling in an electromagnetic band gap, S.Doiron,A.Hache,H.Winful

Abstract

The title of this article is misleading. The authors have investigated a resonator but not a tunneling barrier see also Refs.\cite{Winful2} The measured superluminal group velocity and discussed is that studied on a Lorentz-Lorenz oscillator by Sommerfeld and Brillouin a hundred years ago \cite{Brillouin}. It is similar to the faster than light experiment by Wang et al. based also on anomalous dispersion with a complex refractive index of a resonator \cite{Wang}. Tunneling, however, is understood and performed by electromagnetic evanescent modes or by tunneling solutions of the Schr\"odinger equation, which have purely imaginary wave numbers. The latter includes a purely imaginary refractive index. Signals with purely evanescent frequency components can travel at a superluminal velocity \cite{NimtzH,Nimtz1}. Inside the barrier tunneling proceeds even instantaneously, i.e.by a process described by virtual photons \cite{Stahlhofen}.