Tunable g factor and phonon-mediated hole spin relaxation in Ge/Si nanowire quantum dots

We theoretically consider g factor and spin lifetimes of holes in a longitudinal Ge/Si core/shell nanowire quantum dot that is exposed to external magnetic and electric fields. For the ground states, we find a large anisotropy of the g factor which is highly tunable by applying electric fields. This tunability depends strongly on the direction of the electric field with respect to the magnetic field. We calculate the single-phonon hole spin relaxation times T₁ for zero and small electric fields and propose an optimal setup in which very large T₁ of the order of tens of milliseconds can be reached. Increasing the relative shell thickness or the longitudinal confinement length further prolongs T₁. In the absence of electric fields, the dephasing vanishes and the decoherence time T₂ is determined by T₂=2T₁.