Suppressing charge-noise sensitivity in high-speed Ge hole spin-orbit qubits

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 may expose the qubit to electrical noise, facilitating decoherence. Here we show that, unlike electron spin qubits, the hole spin-3/2 leads generically to sweet spots in the dephasing rate of gate-defined hole qubits as a function of the gate electric field. At these sweet spots, the dephasing rate vanishes to first order in the perpendicular electric field, the EDSR dipole moment is maximized, and the relaxation rate can be drastically reduced by working at small magnetic fields. The existence of the sweet spots is traced to properties of the Rashba spin-orbit interaction unique to spin-3/2 systems. Our results suggest that the coherence of Ge hole spin qubits in quantum dots can be optimized at sweet spots where rapid electric control is also possible, characteristics that make hole spin qubits very favourable for scalable quantum computing.