Fractional phenomena of the spontaneous emission of a two-level atom in photonic crystals

TL;DR

This paper introduces fractional calculus as a novel mathematical approach to analyze the spontaneous emission of a two-level atom in photonic crystals, revealing long-time memory effects and challenging previous findings about atom-photon bound states.

Contribution

The study applies fractional calculus to model atom-field interactions in photonic crystals, providing a more accurate description of long-time dynamics and correcting earlier results.

Findings

Long-time memory effects are fractional phenomena.

No steady photon-atom bound state near the band edge.

Fractional calculus offers a concise and rigorous solution method.

Abstract

We suggest a better mathematical method, fractional calculus, for studying the behavior of the atom-field interaction in photonic crystals. By studying the spontaneous emission of an atom in a photonic crystal with one-band isotropic model, we found that the long-time inducing memory of the spontaneous emission is a fractional phenomenon. This behavior could be well described by the fractional calculus. And the results show no steady photon-atom bound state for the atomic resonant transition frequency lying in the proximity of allowed band edge which is encountered in the previous study [J. Opt. B: Quantum Semiclass. Opt. {\bf 5}, R43 (2003)]. The correctness of this result is validated by the ``cut-off smoothing'' density of photon states (DOS) with fractional calculus. By obtaining a rigorous solution without the multiple-valued problem for the system, we show the method of fractional calculus has logically concise property.