Evidence for macroscopic quantum tunneling of phase slips in long one-dimensional superconducting Al wires.

Quantum phase slips have received much attention due to their relevance to superfluids in reduced dimensions and to models of cosmic string production in the early universe. Their establishment in one-dimensional superconductors has remained controversial. Here we study the nonlinear current-voltage characteristics and linear resistance in long superconducting Al wires with lateral dimensions approximately 5 nm. We find that, in a magnetic field and at temperatures well below the superconducting transition, the observed behaviors can be described by the nonclassical, macroscopic quantum tunneling of phase slips, and are inconsistent with the thermal activation of phase slips.