Stark tuning of electronic properties of impurities for quantum computing applications

Understanding the behavior of donor bound electronic states under electric and magnetic fields is a fundamental issue critical both to the development of novel quantum technologies and to the on-going miniaturization of semiconductor devices. Single donor systems in silicon have already been proposed as the building blocks of a potentially scalable quantum computer that draws upon the vast experience of the semiconductor industry and takes advantage of long spin coherence times. We employed an atomistic tight-binding technique with several million atoms to to provide the most precise and comprehensive investigation of quantum control of donor electrons in semiconductors.;We investigate the electric field response of donor hyperfine constants and effective g-factors, resolving past discrepancies between experiments and theory, and in the process, characterizing some single spin control parameters for a donor qubit. Our Stark effect simulations involving a single donor near a semiconductor-insulator interface demonstrates the gate induced adiabatic ionization and dimensional symmetry transition of the donor electron from a 3D atomic Coulomb well to a 2DEG-type system, and was able to explain recent transport spectroscopy measurements on single donors. The ability to induce such symmetry transitions is a critical functionality requirement in donor qubits. We also investigate gate controlled single electron localization in multiple donor wells in order to explore charge qubit design issues and to verify a coherent electron tunneling mechanism across a donor chain. Finally, two-electron states of donor molecules in the presence of electric fields are computed using many-body methods in order to study exchange energy, a quantity of interest for two-qubit operations.