Coherence and Quantization in Nearly Superconducting Rings

Abstract

New experiments demonstrating macroscopic coherence and quantization in partially resistive superconducting rings with point contacts are described. These include: (1) the observation of quantized magnetic transitions for frequencies $\omega >{\omega }_1=\frac{R}{L}$, where $R$ is the resistance and $L$ the inductance of the ring, and (2) the measurement of coherent oscillations at frequencies limited by thermal noise fluctuations, $\frac{8k_B\mathrm{TR}}{{{\Phi }_0}^2}$, where $k_B$ is Boltzmann's constant, $T$ the absolute temperature, and ${\Phi }_0$ the flux quantum. These results are interpreted by introducing into the phenomenological model of weakly connected superconducting rings a continuous time dependence of the quantum states.