Vortex matter in active and passive superconducting devices

In this contribution it is demonstrated (i) that active as well as passive superconducting devices can be used as very sensitive tools for detecting motion and penetration of vortices in superconducting material and (ii) that the analysis of the distribution of vortices in the device can be used for optimization of these devices for application. The potential for applications of superconducting devices strongly depends upon the reduction of dissipative processes due to vortex motion. Whereas vortex motion in active devices leads among others to increased low-frequency noise and, thus, reduces the sensitivity of e.g. SQUIDs, vortices in microwave devices reduce the quality factor and, finally, the power handling capability. For both types of devices vortex penetration at extremely low magnetic induction can be observed and the position of penetrating vortices can be deduced by adequate analysis of the recorded magnetic flux or power handling property for SQUIDs or resonator, respectively. The effect of vortex penetration and trapping of flux - for instance by strategically positioned antidots - upon the performance of the device will be demonstrated and, finally, methods to reduce or avoid the negative impact of vortices in these devices are sketched