NC State University

III - V Pillar Quantum Computer

We have designed and modeled a computer design that consists of a vertical stack of coupled asymmetric quantum dots in a superlattice III-V pillar configuration with each dot having a unique size and material composition so that its energy structure is different from all other dots in the pillar. Asymmetric dots produce a large dipole moment between ground and excited states so that electrons trapped in adjacent dots are strongly coupled through an electric dipole-dipole interaction. The asymmetric potential of each dot is also designed so that dephasing due to electron-phonon scattering and spontaneous emission is strongly minimized. The combination of strong dipole-dipole coupling to produce rapid calculation rates and the long dephasing time make it possible to perform a sufficient number of computational steps prior to loss of coherence.

ECE Nano Image - QD Potential Energy

This quantum computer is similar to the single electron transistor structure recently reported by Tarucha. Like Tarucha's structure, our pillar also contains a source/drain structure and a cylindrical gate electrode. While maintaining zero bias on the source and drain, a large negative bias is applied to the gate that depletes charge carriers near the surface and provides confinement in the radial direction. In the strong depletion regime, the curvature of the parabolic radial potential is a function of the doping concentration, and raises radial energy states above the first excited state along the z-axis to eliminate them from consideration. The insertion of an electron in each dot is accomplished by adjusting the doping concentration to that the quantum dot ground state lies close to the Fermi level as shown below.

ECE Nano Image - QD Pillar Energy

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