  Once the periodic properties of elements were unveiled, chemical bonds could
be understood in terms of the valence of atoms. Ideally, this rationale would
extend to quantum dots, often termed artificial atoms, and quantum computation
could be performed by merely controlling the outer-shell electrons of dot-based
qubits. Imperfections in the semiconductor material, including at the atomic
scale, disrupt this analogy between atoms and quantum dots, so that real
devices seldom display such a systematic many-electron arrangement. We
demonstrate here an electrostatically-defined quantum dot that is robust to
disorder, revealing a well defined shell structure. We observe four shells (31
electrons) with multiplicities given by spin and valley degrees of freedom. We
explore various fillings consisting of a single valence electron -- namely 1,
5, 13 and 25 electrons -- as potential qubits, and we identify fillings that
yield a total spin-1 on the dot. An integrated micromagnet allows us to perform
electrically-driven spin resonance (EDSR). Higher shell states are shown to be
more susceptible to the driving field, leading to faster Rabi rotations of the
qubit. We investigate the impact of orbital excitations of the p- and d-shell
electrons on single qubits as a function of the dot deformation. This allows us
to tune the dot excitation spectrum and exploit it for faster qubit control.
Furthermore, hotspots arising from this tunable energy level structure provide
a pathway towards fast spin initialisation. The observation of spin-1 states
may be exploited in the future to study symmetry-protected topological states
in antiferromagnetic spin chains and their application to quantum computing.
