Simplified description of an active medium in quantum plasmonics

摘要

In order to simplify the theoretical description of spasers, a gain medium iscommonly represented by a two-level system. A realistic model, however, shouldhave four levels. By using the Lindblad equations we develop a description ofsuch a system and show that depending on ratios of the Rabi frequency and therate of relaxation of the polarization, a four-level system may be reduced toone of two effective two-level systems that reproduce the key properties of afour-level system.