  Temporal universal conductance fluctuations (TUCF) are observed in RuO$_2$
nanowires at cryogenic temperatures. The fluctuations persist up to very high
$T \sim 10$ K. Their root-mean-square magnitudes increase with decreasing $T$,
reaching $\sim 0.2 e^2/h$ at $T \lesssim 2$ K. These fluctuations are shown to
originate from scattering of conduction electrons with rich amounts of mobile
defects in artificially synthesized metal oxide nanowires. TUCF characteristics
in both one-dimensional saturated and unsaturated regimes are identified and
explained in terms of current theories. Furthermore, the TUCF as a probe for
the characteristic time scales of the mobile defects (two-level systems) are
discussed.
