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Tunable resonator and tuning speed measurement setup. (a) A schematic of a tunable resonators with a micrograph of the terminating array of six SQUIDs. There are two on-chip flux lines; one for fast pulses and one for the DC flux bias. The area of each of the SQUID loops is and the distance is for the sample measured ( in the picture). The devices are fabricated on a silicon substrate with a layer of wet-grown silicon dioxide. The cavity and the Josephson junctions forming the SQUIDs are fabricated from aluminum in a single lithography step using double angle evaporation and oxidation. (b) Schematic of the measurement setup used to detect rapid changes in the resonance frequency.
Microwave reflectometry measurements. (a) Resonance frequency for the two samples A and B. (b) values with a fit assuming low subgap resistance. (c) Detuning in line widths as a function of detuning. Solid line is a fit to sample A.
Fast tuning measurements. (a) Mixing the signal from the resonator with the drive frequency and filtering out the high frequency components as we apply a fast flux pulse to the SQUIDs. We observe a decaying, oscillating signal where the frequency of the oscillations is the difference frequency of the drive and the detuned resonance frequency. Inset: the pulse used to detune the resonance frequency. The amplitude of the pulse sets how far the resonator is detuned. (b) Resonance frequency obtained from fast pulse measurements as a function of flux pulse amplitude. We can both increase and decrease the frequency with the fast pulse meaning that we can both stretch and compress the wavelength of the field stored in the resonator. Solid line: fit to the VNA measurements. (c) Signal when a flux pulse is applied. The detuning is , obtained from the period of the oscillations.
Parameters of the two measured devices. is the number of SQUIDs, is the critical current of the Josephson junctions, is the zero-flux resonance frequency, is the maximum detuning achieved, is the zero field value, and the last column states how the flux bias was applied to the SQUID.
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