Good news everyone! Our paper Linear-in-momentum spin orbit interactions in planar Ge/GeSi heterostructures and spin qubits just got published!!

When hole spins in Ge are confined near an interface, as is usually the case for spin qubits, there is a symmetry reduction that leads to linear-in-momentum spin-orbit interactions in the heavy-hole manifold. These interface terms are not very strong but induce contributions to the manipulabity of hole spins for both in-plane and vertical mangetic fields. Moreover, they introduce a tilt in the in-plane response, which leads to an in-plane anisotropy of g-factors and the Rabi frequencies. One important detail about these interactions is that they get partially removed by disorder, explaining part of the variability of Ge qubits, however, as interfaces become cleaner, these linear effects will become more apparent.