  Semiconductor/superconductor hybrids exhibit a range of phenomena that can be
exploited for the study of novel physics and the development of new
technologies. Understanding the origin the energy spectrum of such hybrids is
therefore a crucial goal. Here, we study Josephson junctions defined by shadow
epitaxy on InAsSb/Al nanowires. The devices exhibit gate-tunable supercurrents
at low temperatures and multiple Andreev reflections (MARs) at finite voltage
bias. Under microwave irradiation, photon assisted tunneling (PAT) of MARs
produces characteristic oscillating sidebands at quantized energies, which
depend on MAR order, $n$, in agreement with a recently suggested modification
of the classical Tien-Gordon equation. The scaling of the quantized energy
spacings with microwave frequency provides independent confirmation of the
effective charge $ne$ transferred by the $n^\mathrm{th}$ order tunnel process.
The measurements suggest PAT as a powerful method for assigning the origin of
low energy spectral features in hybrid Josephson devices.
