Quantitative analysis of quantum phase slips in superconducting Mo ₇₆Ge ₂₄ nanowires revealed by switching-current statistics

We measure quantum and thermal phase-slip rates using the standard deviation of the switching current in superconducting nanowires. Our rigorous quantitative analysis provides firm evidence for the presence of quantum phase slips (QPSs) in homogeneous nanowires at high bias currents. We observe that as temperature is lowered, thermal fluctuations freeze at a characteristic crossover temperature T _q, below which the dispersion of the switching current saturates to a constant value, indicating the presence of QPSs. The scaling of the crossover temperature T _q with the critical temperature T _c is linear, T _qT _c, 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.