  Quantum devices based on InSb nanowires (NWs) are a prime candidate system
for realizing and exploring topologically-protected quantum states and for
electrically-controlled spin-based qubits. The influence of disorder on
achieving reliable topological regimes has been studied theoretically,
highlighting the importance of optimizing both growth and nanofabrication. In
this work we investigate both aspects. We developed InSb nanowires with
ultra-thin diameters, as well as a new gating approach, involving few-layer
graphene (FLG) and Atomic Layer Deposition (ALD)-grown AlOx. Low-temperature
electronic transport measurements of these devices reveal conductance plateaus
and Fabry-P\'erot interference, evidencing phase-coherent transport in the
regime of few quantum modes. The approaches developed in this work could help
mitigate the role of material and fabrication-induced disorder in
semiconductor-based quantum devices.
