Magnetic flux noise in the three Josephson junctions superconducting ring

We analyze the influence of noise on magnetic properties of a superconducting loop which contains three Josephson junctions. This circuit is a classical analog of a persistent current (flux) qubit. A loop supercurrent induced by external magnetic field at the presence of thermal fluctuations is calculated. In order to get connection with experiment we calculate the impedance of the low-frequency tank circuit which is inductively coupled with a loop of interest. We compare obtained results with the results in quantum mode when the three junction loop exhibits quantum tunneling of the magnetic flux. We demonstrate that the tank-loop impedance in the classical and quantum modes have different temperature dependence and can be easily distinguished experimentally. PACS: 85.25.Am Superconducting device characterization, design, and modeling; 85.25.Hv Superconducting logic elements and memory devices; microelectronic circuits.