An electrically isolated Josephson junction array as a tunable metamaterial

Abstract

We report low-temperature microwave transmission measurements on a superconducting metamaterial composed of an electrically isolated two-dimensional Josephson junction (JJ) array. Each plaquette, which acts as a meta-atom, is a square loop with a single JJ centered on each side. The collective response of approximately 30 000 coupled meta-atoms produces a sharp, robust resonance in transmission. The resonance can be switched on and off, and its frequency and amplitude tuned, by varying temperature or incident microwave power. Above a threshold rf power of approximately −49 dBm the resonance evolves into multiple discrete transmission features with uniform frequency spacing. These observations indicate a power-dependent nonlinear response, consistent with frequency-locking phenomena in Josephson systems. Moreover, our results demonstrate how an unbiased JJ array can function as a nonlinear, tunable electromagnetic metamaterial in the microwave regime.