We construct a class of Hamiltonians that describe the photodetection process from beginning to end. Our Hamiltonians describe the creation of a photon, how the photon travels to an absorber (such as a molecule), how the molecule absorbs the photon, and how the molecule after irreversibly changing its configuration triggers an amplification process-at a wavelength that may be very different from the photon's wavelength-thus producing a macroscopic signal. We use a simple prototype Hamiltonian to describe the single-photon detection process analytically in the Heisenberg picture, which neatly separates desirable from undesirable effects. Extensions to more complicated Hamiltonians are pointed out.

With the aid of a coherent transport model utilizing the Non-Equilibrium Green Function (NEGF) approach, a three terminal device with metallic gate, source and drain and a quasi one dimensional Charge Density Wave (CDW) channel is simulated focussing on the transistor behaviour brought about by a sweep of the channel potential or equivalently the chemical potential in the channel. The channel is strongly insulating only at half-filling and moving to lower and higher carrier concentrations both incur a mean field phase transition to a conducting state. With the aid of conductance calculations for a pinned CDW condensate, we present calculations for the sub-threshold slope in terms of the hopping parameter or equivalently the width of the tight-binding chain. The effects of source to drain bias and length are examined. The conductance profiles are analyed in relation to transmission profiles. The observed CDW profiles are explained in terms of filling and Fermi Surface Nesting (FSN). Boundary conditions, gap equations and response functions are shown to reveal the commensurability conditions and size of the transport gap. The channel carrier concentration is modulated in an athermal (non-Maxwellian-Boltzmann) fashion, thereby making it an interesting prospect for steep transistors.

A quantitative measure of how much the inclusion of the conduction band-valence band coupling effects influence the band structure was obtained. The numerical results of two formalisms were derived using Finite Difference Method (FDM) where one formalism ignores the coupling effects between conduction and valence bands. It was found that the conduction band-valence band coupling effects significantly affects the band structure of typical InGaN Quantum Wells (QW) especially the conduction subbands.

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