  Clean one-dimensional electron systems can exhibit quantized conductance. The
plateau conductance doubles if the transport is dominated by Andreev
reflection. Here, we report quantized conductance observed in both Andreev and
normal-state transports in PbTe-Pb and PbTe-In hybrid nanowires. The Andreev
plateau is observed at $4e^2/h$, twice of the normal plateau value of $2e^2/h$.
In comparison, Andreev conductance in the best-optimized III-V nanowires is
non-quantized due to mode-mixing induced dips (a disorder effect), despite the
quantization of normal-state transport. The negligible mode mixing in PbTe
hybrids indicates an unprecedented low-disorder transport regime for nanowire
devices, beneficial for Majorana researches.
