As a second basic research line, we implement microwave circuits with integrated Josephson junctions and superconducting quantum interference devices (SQUIDs). Josephson elements constitute a nonlinear inductance and therefore the resulting Josephson microwave circuit will be both nonlinear and tunable in frequency/linewidth by an externally applied current or magnetic field. On the one hand, such Josephson and quantum interference circuits can be used to investigate the basic properties of the integrated Josephson junctions, such as its current-phase-relation or a potential Josephson-diode effect. On the other hand, these circuits are highly sensitive detectors for small currents, magnetic flux, or mechanical displacement. Finally, they can be tuned in and out of resonance with other devices by changing the flux through the SQUID, and they can be dynamically modulated to realize quantum-limited parametric amplifiers. Our focus is the development and investigation of high-quality quantum interference circuits based on niobium and YBCO with novel types of focused-ion-beam enabled Josephson junctions, compatible with high magnetic fields and operable over a wide range of temperatures from 10 mK to several K.
Funded by the German Research Foundation (DFG) via grant no. 490939971 (PI: Daniel Bothner), grant no. 511315638 (PI: Daniel Bothner), and grant no. 583391775 (PI: Daniel Bothner).
