Measurement of the probability distribution of thermally excited fluxoid quantum transitions in a superconducting ring closed by a Josephson junction

The thermally induced distribution of transitions between fluxoid quantum states of a superconducting ring closed by a Josephson junction has been measured. The observed dependence of its width $\sigma$ on temperature, ring inductance, and weak-link critical current, as well as its shape, confirms the recent theoretical results of Kurkijärvi, $\sigma \propto L{\left(i_c\right)}^{\frac{1}{3}}{T}^{\frac{2}{3}}$.