Entanglement of Λ-atom and thermal photons in a double-band photonic crystal

Abstract

The entanglement of Λ-type three-level atoms and thermal photons in a nanocavity inside a double-band photoniccrystal is studied. The partially transposed density matrix and, consequently,the negativity, as a measure of entanglement, are determined at a temperatureT. By analyzing the eigenvalues of the partially transposed density matrix, we show that thethermal atom–field states remain coherent for all temperatures. Furthermore, plots of thenegativity indicate that at a definite temperature, which strongly depends upon thelocation of the photonic band gaps, the entanglement is maximal. How the location of thephotonic band gaps, relative to the atomic transition frequencies, affects this temperatureis also addressed.