Quantum Dot Spin Qubits: Decoherence from Nearby Impurities

We study the undesired exchange coupling between quantum dot spin qubits and other nearby electronic spins trapped on dopant impurities. Such coupling is a source of decoherence. The problem is treated in the context of a 2DEG heterostructure, with strong, local electric fields. For silicon-based systems, we develop the theory of the Stark effect for P:Si in a degenerate conduction band. We investigate the resulting Stark energy spectrum and the field dependence of the valley composition parameters.