Quantum and semiclassical scattering dynamics

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Advances in nanotechnology are a window into the microscopic realm of electrons, atoms and molecules. The dynamics, at this level, is quantum mechanical. There is much to be learned from the computation of exact quantum dynamics for such systems. Exotic quantum phenomena, without parallel in the familiar classical world, can play a central role - phenomena such as tunneling, nonadiabatic transition and resonance. Tunneling through an array of barriers gives rise to transmission resonances - peaks in transmission probability to near unity. Since between resonances, transmission probability is very small, this phenomenon could be the basis for a quantum switch which controls the current of a single electron. However, a closer look at the transmitting electron reveals that there is a significant chance of it sticking to the barriers, and taking a long time to transmit. This could limit the performance of the device in an application. The problem can be overcome by adjusting the barriers - effectively adding an anti-reflection coating to the array - such that the sharp transmission resonances morph into a smooth transmission band exhibiting rapid transmission. Reflection resonances are also possible. For example, they arise from avoided crossings between quantum levels associated with motion in directions other than the transmission direction. We propose to investigate the modification of avoided-crossing arrays in order to blend sharp reflection resonances into smooth reflection bands, with slow reflection replaced by rapid reflection. In addition to accurate quantum computations, a semiclassical treatment of the dynamics will be provided. This amounts to a description of the quantum dynamics as the interference of simple waves associated with specific paths across the device - including reflections and interchange of quantum levels. Other studies address the time development of population inversion in the fluorine + methane chemical laser reaction, and unexpected rates of gas phase organic reactions. See www.chemistry.mcmaster.ca/dumont/ for more information.