This proposal describes the progress made in our present NSF grant 1 and proposes to continue our research to further investigate the properties of single electrons trapped within a vertical quantum dot. A technique has been developed to fabricate metal electrodes on the oxide insulated surface of silicon at dimensions ~ 60 nanometers so that with an appropriate applied voltage at low temperature, a single electron is trapped at either the silicon to silicon-oxide interface or at a silicon to silicon-carbide heterostructure interface of a suitably grown heteroepitaxial structure. Preliminary theoretical calculations, similar to those used in the design of a if pillar quantum computer lo 2 have been employed to predict the stable regions where a single and a few electrons can be trapped in these vertical quantum dot structures, and to estimate the magnitude of the exchange coupling between neighboring quantum dots as a function of the separation distance. A linear array of these quantum dots in a device design that allows independent addressing of the trapped electron spin states when the structure is in an external magnetic field, as described in the Project Description, define a quantum computer application for these devices. Herein we propose to fabricate additional devices and conduct low temperature electrical and magnetic-resonance measurements to verify the trapping dynamics of these quantum dots. To accomplish this, special low temperature solid-state amplifiers will be designed with the sensitivity required to make the measurements and perform the impedence transformation necessary to drive the signal lines for room temperature acquisition of the information. Initial measurements will examine many dots connected in parallel. These will be followed by examination of quantum dot pairs where the separation produces exchange coupling to study the nearest neighbor interactions. We will use similar quantum dot device structures with a suitably interconnected quantum dot arrays to make low temperature electron spin resonance measurements to determine the spin resonance properties. The g-factor, spin-lattice relaxation time (T1), the coherence time (T2), and nearest neighbor effects will be determined.
Graduate students within our group at NCSU will conduct the research in collaboration with our colleagues and students at the University of North Carolina who have millikelvin temperature electrical measurement capability. With successful conclusion of this research initiative, the societal impact could be extremely beneficial by providing a scalable quantum computer. Our nation will benefit from having available this most advanced computational capability for military and commercial use. The need for this advance is evidenced by the intense interest of the National Science Foundation, the National Security Agency, and the Department of Defense in this area.
