  PbTe nanowires coupled to a superconductor have recently been proposed as a
potential Majorana platform. The hallmark of the one-dimensional nature of
ballistic nanowires is their quantized conductance. Here, we report the
observation of conductance plateaus at multiples of the quantized value
$2e^2/h$ in PbTe nanowires at finite magnetic fields. The quantized plateaus,
as a function of source-drain bias and magnetic field, allow for the extraction
of the Land\'e $g$-factor, sub-band spacing and effective mass. The coefficient
of 2 in the plateau conductance indicates the presence of valley degeneracy
arising from the crystal orientation of the nanowires, which are grown on a
(001) substrate. Occasionally, this degeneracy can be lifted by a gate voltage
that breaks the mirror symmetry. Our results demonstrate the one-dimensionality
of PbTe nanowires and fulfill one of the necessary conditions for the
realization of Majorana zero modes.
