| Little-type phase slips are topological fluctuations that carry the superconducting order-parameter field between distinct current-carrying states. Owing to Little's phase slips (LPS), superconducting nanowires acquire electrical resistance. In such wires, it is well known that at higher temperatures LPS occur through the process of thermal barrier-crossing by the order-parameter field. At low temperatures, the general expectation is that LPS should proceed through quantum tunnelling events, which are known as quantum phase slips (QPS). However, resistive measurements have produced evidence both for and against the occurrence of QPS. I will present evidence for the observation of individual QPS events in thin wires at high bias currents. The phase slips are detected through measurements of the distribution of switching currents for which the width exhibits a rather counter-intuitive, monotonic increase with decreasing temperature. Importantly, measurements show that in nanowires with larger critical currents, quantum fluctuations dominate thermal fluctuations up to higher temperatures. |
|