  Strong spin-orbit interactions make hole quantum dots central to the quest
for electrical spin qubit manipulation enabling fast, low-power, scalable
quantum computation. Yet it is important to establish to what extent spin-orbit
coupling exposes qubits to electrical noise, facilitating decoherence. Here,
taking Ge as an example, we show that group IV gate-defined hole spin qubits
generically exhibit optimal operation points, defined by the top gate electric
field, at which they are both fast and long-lived: the dephasing rate vanishes
to first order in electric field noise along all directions in space, the
electron dipole spin resonance strength is maximised, while relaxation is
drastically reduced at small magnetic fields. The existence of optimal
operation points is traced to group IV crystal symmetry and properties of the
Rashba spin-orbit interaction unique to spin-3/2 systems. Our results overturn
the conventional wisdom that fast operation implies reduced lifetimes, and
suggest group IV hole spin qubits as ideal platforms for ultra-fast, highly
coherent scalable quantum computing.
