  Semiconductor nanowires have opened new research avenues in quantum transport
owing to their confined geometry and electrostatic tunability. They have
offered an exceptional testbed for superconductivity, leading to the
realization of hybrid systems combining the macroscopic quantum properties of
superconductors with the possibility to control charges down to a single
electron. These advances brought semiconductor nanowires to the forefront of
efforts to realize topological superconductivity and Majorana modes. A prime
challenge to benefit from the topological properties of Majoranas is to reduce
the disorder in hybrid nanowire devices. Here, we show ballistic
superconductivity in InSb semiconductor nanowires. Our structural and chemical
analyses demonstrate a high-quality interface between the nanowire and a NbTiN
superconductor which enables ballistic transport. This is manifested by a
quantized conductance for normal carriers, a strongly enhanced conductance for
Andreev-reflecting carriers, and an induced hard gap with a significantly
reduced density of states. These results pave the way for disorder-free
Majorana devices.
