Magnetic flux noise in the three Josephson junctions superconducting ring

TL;DR

This paper investigates how thermal and quantum fluctuations affect the magnetic properties of a superconducting loop with three Josephson junctions, providing insights into distinguishing classical and quantum behaviors through impedance measurements.

Contribution

It introduces a comparative analysis of classical thermal fluctuations and quantum tunneling effects in a three-junction superconducting loop, linking theoretical predictions with experimental impedance measurements.

Findings

Classical and quantum modes show distinct temperature-dependent impedance behaviors.

Thermal fluctuations influence the supercurrent and magnetic response of the loop.

Quantum tunneling leads to different impedance signatures that can be experimentally distinguished.

Abstract

We analyze the influence of noise on magnetic properties of a su- perconducting 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 in the presence of thermal fluctuations is calculated. In order to get connection with experiment we calculate the impedance of the low-frequency tank cir- cuit 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 quan- tum modes have different temperature dependence and can be easily distinguished experimentally.