  We measure quantum and thermal phase-slip rates using the standard deviation
of the switching current in superconducting nanowires at high bias current. Our
rigorous quantitative analysis provides firm evidence for the presence of
quantum phase slips (QPS) in homogeneous nanowires. We observe that as
temperature is lowered, thermal fluctuations freeze at a characteristic
crossover temperature Tq, below which the dispersion of the switching current
saturates to a constant value, indicating the presence of QPS. The scaling of
the crossover temperature Tq with the critical temperature Tc is linear, which
is consistent with the theory of macroscopic quantum tunneling. We can convert
the wires from the initial amorphous phase to a single crystal phase, in situ,
by applying calibrated voltage pulses. This technique allows us to probe
directly the effects of the wire resistance, critical temperature and
morphology on thermal and quantum phase slips.
