Oral: Sweet spots and sweet lines in Ge/GeSi hole spin qubits

We theoretically investigate sweet spots and sweet lines in Ge/GeSi hole spin qubit heterostructures with different symmetries (disk-shaped, squeezed and displaced hole quantum dots, under homogeneous and inhomogeneous strains). We monitor Rabi frequencies, coherence times and quality factors as a function of magnetic field orientation and look for the optimal driving configuration. We establish, in particular, a general classification of the geometrical nature of sweet magnetic field orientations where the Larmor frequency of the hole spin decouples from electrical noise. We show that the optimal operation point practically results from the interplay between the sweet spots and lines of different classes of relevant perturbations. In general, the optimal magnetic field orientation (best quality factor) is near the plane of the heterostructure, but can wiggle around in the presence of shear strains. Our results provide guidelines to find high-coherence operation points for hole spin qubits, and for the design of devices more resilient to noise.