  Superconducting qubits are sensitive to a variety of loss mechanisms
including dielectric loss from interfaces. By changing the physical footprint
of the qubit it is possible to modulate sensitivity to surface loss. Here we
show a systematic study of planar superconducting transmons of differing
physical footprints to optimize the qubit design for maximum coherence. We find
that qubits with small footprints are limited by surface loss and that qubits
with large footprints are limited by other loss mechanisms which are currently
not understood.
