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We investigate the effects of extension and overlap of wavefunctions on the dispersion relations of plasmon modes in symmetric double-quantum-well structures. We compare the approximate results in two-dimensional layer-gas (2DLG) model with the exact ones where the extension and overlap of the wavefunctions are included. Our numerical results show that the 2DLG model is a good approximation only in the wide barrier case in the long wavelength limit. When the barrier is thin, the extension and overlap of the wavefunctions cannot be neglected. We also show that the long wavelength gap of the inter-subband mode is proportional to the energy difference between the ground and the first excited energy levels.

We put forward a general classical approach to obtain the quantum dipole-dipole interaction (DDI) between two two-level "atoms" in arbitrary nanostructures, in which the transfer rate of the DDI is analytically expressed as the difference between the two classical dipoles' total radiation power and the sum of the two individual dipole's radiation powers. The radiation power can be calculated by the finite-difference time-domain method. We apply the theory to investigate the DDI in a photonic crystal nanocavity. It is found that strong DDI at a distance can be achieved under resonant conditions and with a high quality factor, and the attractive or repulsive properties of the DDI can be manipulated. Our results should be significant for solid-state quantum-information processing based on the DDI [ABSTRACT FROM AUTHOR]

We present a fast and efficient method to compute photonic orientation-dependent local density of states (ODLDOS) in photonic crystals (PCs) based on the point group transform of the vector field. We swiftly calculate the ODLDOS by this method and acquire the same results as that computed based on many more k points in half of the first Brillouin zone (FBZ) in face-center-cubic (fee) photonic crystals. As an example, we also apply this method to investigate the properties of woodpile photonic crystals and find the remarkable differences in the ODLDOS along different polarization directions. [ABSTRACT FROM AUTHOR]