Wireless Josephson Junction Arrays as Tunable Metamaterials: Inducing Discrete Frequency Steps with Microwave Radiation

TL;DR

This study demonstrates a wireless Josephson junction array acting as a tunable nonlinear metamaterial that exhibits discrete frequency steps induced by microwave radiation, with potential applications in quantum and microwave technologies.

Contribution

It introduces a novel wireless 2D Josephson junction array as a tunable metamaterial that shows quantized frequency steps without a dc bias, expanding the understanding of Josephson effects in metamaterials.

Findings

Resonance splitting into multiple discrete frequencies over 240 MHz range.

Resonance can be switched on/off and tuned via temperature, rf power, or magnetic field.

Array exhibits high quality factor of 2800 at low temperatures.

Abstract

We report low temperature, microwave transmission measurements on a new switchable and tunable class of nonlinear metamaterials. A wireless two dimensional array of Josephson junctions (JJ) is probed as a metamaterial where each plaquette in the array is considered as a meta-atom. In the presence of microwaves, this compact metamaterial of 30,000 connected meta-atoms synchronizes the flow of Cooper pairs to yield a single robust resonant signal with a quality factor of 2800 at the lowest temperature for our measurements. The transmission signal is switched on and off and its amplitude and frequency are tuned with either temperature, incident rf power or dc magnetic field. Surprisingly, increasing the incident rf power above a threshold causes the resonance to split into multiple discrete resonances that extend over a range of 240 MHz for a wide temperature window. We posit that this effect is a new incarnation of the inverse ac Josephson effect where the Josephson plasma frequency locks to the rf drive frequency generating quantized frequency steps, instead of voltage steps, in the absence of a dc bias.