  Superconducting circuits are well established as a strong candidate platform
for the development of quantum computing. In order to advance to a practically
useful level, architectures are needed which combine arrays of many qubits with
selective qubit control and readout, without compromising on coherence. Here we
present a coaxial circuit QED architecture in which qubit and resonator are
fabricated on opposing sides of a single chip, and control and readout wiring
are provided by coaxial wiring running perpendicular to the chip plane. We
present characterisation measurements of a fabricated device in good agreement
with simulated parameters and demonstrating energy relaxation and dephasing
times of $T_1 = 4.1\,\mu$s and $T_2 = 5.7\,\mu$s respectively. The architecture
allows for scaling to large arrays of selectively controlled and measured
qubits with the advantage of all wiring being out of the plane.
