  The design of scalable quantum computers will benefit from predictive models
for qubit performance that consider the design and layout of the qubit devices.
This approach, has recently been adopted for superconducting qubits, but has
received little attention for spin qubits in semiconductors. Here, we employ
models for both the device and the quantum mechanical states in the valence
band to theoretically investigate the properties of hole spin qubits in
laterally gated quantum dots in group-IV materials, which have received
significant recent attention. We find that device design impacts qubit
properties in unexpected ways. First, the presence of optimal operation points
where coherence times are long and qubits can be rapidly manipulated results
not only from gate-voltage-induced changes to the Rashba coefficient, but also
from gate-voltage-induced changes to quantum dot radius in real devices, which
impacts g-factor even when inversion symmetry is preserved (Rashba coupling is
zero). Second, the qubit electric manipulation is substantially higher in the
realistic anharmonic potential, by an order of magnitude in the device design
we consider, compared with a harmonic potential assumption, because the
transverse electric dipole of the qubit depends on electrically mediated
couplings to many excited states. Finally, we show that the rapid electric
drive, compatible with long coherence times, can be achieved in the single-hole
regime, with and without strain. These results establish the need for realistic
description of both the device and the quantum mechanical states to support the
design of spin qubit devices, identify new ways to control hole qubit
properties.
