  Flopping mode qubits in double quantum dots (DQDs) allow for coherent
spin-photon hybridization and fast qubit gates when coupled to either an
alternating external or a quantized cavity electric field. To achieve this,
however, electronic systems rely on synthetic spin-orbit interaction (SOI) by
means of a magnetic field gradient as a coupling mechanism. Here we
theoretically show that this challenging experimental setup can be avoided in
heavy-hole (HH) systems in germanium (Ge) by utilizing the sizeable cubic
Rashba SOI. We argue that the resulting natural flopping mode qubit possesses
highly tunable spin coupling strengths that allow for one- and two-qubit gate
times in the nanosecond range when the system is designed to function in an
optimal operation mode which we quantify.
