  Single spin qubits based on phosphorus donors in silicon are a promising
candidate for a large-scale quantum computer. Despite long coherence times,
achieving uniform magnetic control remains a hurdle for scale-up due to
challenges in high-frequency magnetic field control at the nanometre-scale.
Here, we present a proposal for a flopping-mode electric dipole spin resonance
qubit based on the combined electron and nuclear spin states of a double
phosphorus donor quantum dot. The key advantage of utilising a donor-based
system is that we can engineer the number of donor nuclei in each quantum dot.
By creating multi-donor dots with antiparallel nuclear spin states and
multi-electron occupation we can minimise the longitudinal magnetic field
gradient, known to couple charge noise into the device and dephase the qubit.
We describe the operation of the qubit and show that by minimising the
hyperfine interaction of the nuclear spins we can achieve $\pi/2-X$ gate error
rates of $\sim 10^{-4}$ using realistic noise models. We highlight that the low
charge noise environment in these all-epitaxial phosphorus-doped silicon qubits
will facilitate the realisation of strong coupling of the qubit to
superconducting microwave cavities allowing for long-distance two-qubit
operations.
