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.
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.
Metamamterials are 1D, 2D or 3D arrays of articial atoms. The articial atoms, called "meta-atoms", can be any component with tailorable electromagnetic properties, such as resonators, LC circuits, nano particles, and so on. By designing the properties of individual meta-atoms and the interaction created by putting them in a lattice, one can create a metamaterial with intriguing properties not found in nature. My Ph. D. work examines the meta-atoms based on radio frequency superconducting quantum interference devices (rf-SQUIDs); their tunability with dc magnetic field, rf magnetic field, and temperature are studied. The 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. At relatively low rf magnetic field, a magnetic field tunability of the resonant frequency of up to 80 THz/Gauss by dc magnetic field is observed, and a total frequency tunability of 100% is achieved. The macroscopic quantum superconducting metamaterial also shows manipulative self-induced broadband transparency due to a qualitatively novel nonlinear mechanism that is different from conventional electromagnetically induced transparency (EIT) or its classical analogs. A near complete disappearance of resonant absorption under a range of applied rf flux is observed experimentally and explained theoretically. The transparency comes from the intrinsic bi-stability and can be tuned on/ off easily by altering rf and dc magnetic fields, temperature and history. Hysteretic in situ 100% tunability of transparency paves the way for auto-cloaking metamaterials, intensity dependent filters, and fast-tunable power limiters. An rf-SQUID metamaterial is shown to have qualitatively the same behavior as a single rf-SQUID with regards to dc flux, rf flux and temperature tuning. The two-tone response of self-resonant rf-SQUID meta-atoms and metamaterials is then studied here via intermodulation (IM) measurement over a broad range of tone frequencies and tone powers. A sharp onset followed by a surprising strongly suppressed IM region near the resonance is observed. This behavior can be understood employing methods in nonlinear dynamics; the sharp onset, and the gap of IM, are due to sudden state jumps during a beat of the two-tone sum input signal. The theory predicts that the IM can be manipulated with tone power, center frequency, frequency difference between the two tones, and temperature. This quantitative understanding potentially allows for the design of rf-SQUID metamaterials with either very low or very high IM response.
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 80 THz=G at 12 GHz is observed, a total tunability of 56% 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.
\n\nA dynamical crossover regime is revealed when exposing a classical two-dimensional–ordered Josephson junction (JJ) array to evanescent waves and tuning the incident microwave power. At the lowest possible temperature for these experiments, 1.1 K, and at the lowest power setting, −55textdBm , evanescent waves are transmitted without loss and the resonance exhibits a quality factor of sim4200 . A second, smaller resonance, which evolves with increasing power from the main resonance, is also investigated. In contrast to the behavior of the main resonance, this second peak grows as the incident power is increased and does not maintain a fixed resonant frequency for temperatures less than the superconducting critical temperature of niobium. The tunability of both resonances is studied as a function of temperature and microwave power. Finally, we speculate that this dynamical crossover regime is evidence of a transition between two states of phase coherence where at low microwave power the JJ arrays are phase locked and at high microwave power the JJ arrays are unlocked.\n
Superconducting metamaterials show the promise of low loss, compact size and extreme tunability and nonlinearity, allowing for new applications. Most demonstrations of these metamaterials have been conducted in waveguide geometries, either in co-planar form or three-dimensional single-conductor structures. Here we demonstrate for the first time a widely tunable superconducting metamaterial operating under the free-space illumination of a quasi-optical beam in the 100 GHz regime. The meta-atoms are Radio Frequency Superconducting QUantum Interference Devices (RF SQUIDs) that form compact self-resonant objects endowed with the nonlinearity of the Josephson effect. The metamaterial is tuned with dc magnetic flux, temperature and mm-wave power, and holds promise for a new generation of mm-wave agile devices. This work is supported by the NSF-GOALI and OISE programs through grant #ECCS-1158644, and CNAM.
The influence of radio frequency microwaves on the Coulomb blockade characteristics in small Josephson junctions was studied using a one-dimensional array of ten small Al tunnel junctions in the frequency range from 1 MHz to 1000 MHz. Coulomb blockade voltage (Vth) is diminished with increasing microwave power (Vac), where the Vth-Vac plots for varied frequencies fall on a single curve. We observed and theoretically analyzed a magnetic field dependent renormalization of the applied microwave power, in addition to a magnetic-field independent renormalization effect explained using an effective circuit approach of the array. Due to its high sensitivity to microwave power, the array is well-suited for on-chip detection applications in low temperature environments.
We have developed active metamaterials based on macroscopic quantum effects capable of quickly tuning their electrical and magnetic responses over a wide frequency range. These metamaterials are based on superconducting elements to form low insertion loss, physically and electrically small, highly tunable structures for the next generation rf electronics. The meta-atoms are rf superconducting quantum interference devices (SQUIDs) that incorporate the Josephson effect. RF SQUIDs have an inductance which includes a contribution from the Josephson inductance of the junction. This inductance is strongly tunable with dc and rf magnetic fields and currents. The rf SQUID metamaterial is a richly nonlinear effective medium introducing qualitatively new macroscopic quantum phenomena into the metamaterials community, namely magnetic flux quantization and the Josephson effect. The coherence of the metamaterials is strongly sensitive to the environment and measurement conditions. The metamaterials also display a unique form of transparency whose development can be manipulated through multiple parametric dependences. Further features such as breathers, superradiance, and self-induced transparency, along with entry into the fully quantum limit, will yield qualitatively new metamaterial phenomena. This work is supported by the NSF-GOALI and OISE Programs through Grant No. ECCS-1158644 and the Center for Nanophysics and Advanced Materials (CNAM).