  We investigate a semiconductor nanowire-based gatemon qubit with epitaxial Al
on two facets of the nanowire, allowing gate control of wire density. Two
segments have the Al removed, one forming a Josephson junction and the other
operating as a transistor, providing in-situ switching between dc transport and
qubit operation. Gating the NW changes the bulk wire potential distribution,
while gating the Josephson junction changes the number of junction modes. Both
effects are revealed by the dependence of qubit frequency on parallel magnetic
field. A detailed model of the wire and junction yields behavior consistent
with experiment. In the multi-mode regime, fluctuations in qubit frequency are
considerably smaller than the theoretical "universal" value, also smaller than
numerics, and consistent with previous measurements of fluctuating critical
current.
