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 first Ge as an example, I will show that group IV gate-defined hole spin qubits generically exhibit sweet spots, defined by the top gate electric field, at which they are 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 sweet spots is traced to group IV crystal symmetry and properties of the Rashba spin-orbit interaction unique to spin-3/2 systems. I will show that similar findings apply to Si. Our results overturn the conventional wisdom that fast operation implies reduced lifetimes, and suggest group IV hole spin qubits as ideal platforms for ultrafast, highly coherent scalable quantum computing .
1. Zhanning Wang, Elizabeth Marcellina, Alex Hamilton, James Cullen, Sven Rogge, Joe Salfi, and Dimi Culcer, NPJ Quantum Information 7, 54 (2021).