Imaging Coherent Response of Superconducting Metasurface

We study microwave response of the individual metaatoms of a superconducting metasurface formed by a two-dimensional array of superconducting quantum interference devices (SQUIDs). In our experiment, RF currents in the metasurface are directly imaged by using the laser scanning microscopy (LSM) technique. We tested a sample with 21 × 21 SQUID array in a waveguide cavity designed to achieve a uniform microwave distribution over the entire array. The demonstrated tunability of 2D SQUID metasurface resonance frequency by external magnetic field is about 56%, covering 8-12.5-GHz range. The obtained LSM images of the RF current distributions over the SQUID array confirm a high degree of coherence of the entire metasurface. The SQUID-based metasurfaces combine low losses and frequency tunability and can be useful for designing compact cryogenic RF systems.