Coherent phase slips in superconducting nanorings

We study quantum fluctuations of persistent current in a small superconducting ring. Based on a microscopic model of the ring we argue that under certain conditions such ring will exhibit coherent quantum phase slips, similar to those in a flux qubit. We evaluate the frequency of such coherent oscillations and find that it is strongly dependent on wire's diameter primarily due to the large momentum released by the condensate as a result of a phase slip event. We also find that the value of such frequency is not a self-averaging quantity, that is, it depends on a particular realization of the static impurity potential.