Abstract
We have prepared meta-atoms based on radio-frequency superconducting quantum-interference devices (rf SQUIDs) and examined their tunability with dc magnetic field, rf current, and temperature. rf SQUIDs are superconducting split-ring resonators in which the usual capacitance is supplemented with a Josephson junction, which introduces strong nonlinearity in the rf properties. We find excellent agreement between the data and a model that regards the Josephson junction as the resistively and capacitively shunted junction. A magnetic field tunability of at 12 GHz is observed, a total tunability of is achieved, and a unique electromagnetically induced transparency feature at intermediate excitation powers is demonstrated for the first time. An rf SQUID metamaterial is shown to have qualitatively the same behavior as a single rf SQUID with regard to dc flux and temperature tuning.
- Received 26 July 2013
DOI:https://doi.org/10.1103/PhysRevX.3.041029
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Published by the American Physical Society
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This article appears in the following collection:
Special Section on Metamaterials
A Physical Review X special section on the emerging field of metamaterials.
Popular Summary
Imagine a radio that can tune to any frequency and directly digitize the signal even if it is so weak that other receivers would only hear noise, and imagine that this could be done for millions of frequencies every second, so that you would never miss a good song playing on a distant radio station. To achieve this, one would have to solve the problem of discerning the desired signal from the noise and interference from overlapping transmitting stations. This is extremely difficult because a receiver that is sensitive enough to detect a very faint signal will typically saturate if it is also subjected to strong unwanted signals. The solution may come from an unexpected direction—tunable metamaterials. In this experiment, we demonstrate a new kind of metamaterial built with individual radio-frequency superconducting quantum-interference devices that enables extremely fast and long-range tuning, opening a new path to the development of tunable and programmable rf elements for next-generation miniature antennas, filters, and low noise amplifiers.
Each “meta-atom,” a radio-frequency superconducting quantum-interference device (rf SQUID), is a superconducting loop interrupted by a single Josephson junction—a nonsuperconducting tunnel barrier sandwiched between two superconducting electrodes. SQUIDs are not only low in loss and small in size, but the Josephson junction also has a nonlinear effective inductance that can be tuned over a broad range, with dc magnetic field, radio-frequency current, and temperature, leading to a large tunability in the resonant frequency of the whole meta-atom. Indeed, only extremely small magnetic fields are required to make very substantial changes. We have also demonstrated that a two-dimensional array of the rf SQUIDs shows the same remarkable tuning properties as individual SQUIDs. This extraordinarily tunable and nonlinear metamaterial shows great potential for applications in superconducting digital radio systems.