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International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz)

Wirelessly tunable superconducting resonators in the W-band

Debadri Das, Charlotte M. Wehner, Nathan T. Yoho, Emilio Alessandro Nanni

Published Aug 17, 2025• 0 citations
Publisher

Abstract

We are working to develop a high-Q superconducting resonator at mm-wave frequencies, particularly in the W-band (75-110 GHz). The resonator is made out of a high-kinetic inductance material (Niobium Titanium Nitride on Sapphire). The resonance is tuned wirelessly via an uniform axial magnetic field generated by a solenoid. We will characterize the tuning bandwidth of the resonator by sweeping the B-field while performing transmission measurements (S21) in a cryogenic environment at ~1-4 K.

DOI
10.1109/irmmw-thz61557.2025.11319924

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•Jan 1, 2008•0 citations
We are working to develop a high-Q superconducting resonator at mm-wave frequencies, particularly in the W-band (75-110 GHz). The resonator is made out of a high-kinetic inductance material (Niobium Titanium Nitride on Sapphire). The resonance is tuned wirelessly via an uniform axial magnetic field generated by a solenoid. We will characterize the tuning bandwidth of the resonator by sweeping the B-field while performing transmission measurements (S21) in a cryogenic environment at ~1-4 K.
Frequency-tunable microwave resonators are in great demand especially in hybrid systems where precise frequency alignment of resonances is required. Here, we present frequency-tunable high-Q superconducting resonators fabricated from thin niobium nitride and niobium titanium nitride films. The resonant frequency is tuned by applying a magnetic field perpendicular to the hole structures in the resonator's inductor wire, whose kinetic inductance is modified by wirelessly induced DC supercurrents. A continuous in situ frequency tuning of over 300 MHz is achieved for a 10 GHz resonator with a moderate magnetic field of 1.2 mT. The planar resonator design and the noncontact tuning scheme greatly ease the fabrication complexity and can be widely applied in many hybrid systems for coupling microwave modes with other forms of excitations such as optical photons, phonons, magnons, and spins.
We have designed, fabricated, and tested a frequency-tunable high-Q superconducting resonator made from a niobium titanium nitride film. The frequency tunability is achieved by injecting a DC through a current-directing circuit into the nonlinear inductor whose kinetic inductance is current-dependent. We have demonstrated continuous tuning of the resonance frequency in a 180 MHz frequency range around 4.5 GHz while maintaining the high internal quality factor Qi > 180 000. This device may serve as a tunable filter and find applications in superconducting quantum computing and measurement. It also provides a useful tool to study the nonlinear response of a superconductor. In addition, it may be developed into techniques for measurement of the complex impedance of a superconductor at its transition temperature and for readout of transition-edge sensors.
We report on a simple yet versatile design for a tunable superconducting microstrip resonator. Niobium nitride is employed as the superconducting material and aluminum oxide, produced by atomic layer deposition, as the dielectric layer. We show that the high quality of the dielectric material allows to reach the internal quality factors in the order of Qi∼104 in the single photon regime. Qi rapidly increases with the number of photons in the resonator N and exceeds 105 for N∼10−50. A straightforward modification of the basic microstrip design allows to pass a current bias through the strip and to control its kinetic inductance. We achieve a frequency tuning δf=62 MHz around f0=2.4 GHz for a fundamental mode and δf=164 MHz for a third harmonic. This translates into a tuning parameter Qiδf/f0=150. The presented design can be incorporated into essentially any superconducting circuitry operating at temperatures below 2.5 K.
We present a design of a tunable on-chip resonator that can benchmark the nonlinear kinetic inductance (KI) properties of various superconducting thin films in the W-band (75-110 GHz), for quantum device applications. Our design uses a quarter-wavelength microstrip resonator with ground plane cutout for transmission measurements, WR10 input & output ports, DC bias line and radial-stub notch filters to suppress RF leakage into the bias lines. Our resonator design procedure uses simulations with perfect electric conductors as an initial reference case, which will be later replaced by finite-impedance material to include the effect of sheet inductance.
We present a design and implementation of a frequency-tunable superconducting resonator. The resonance frequency tunability is achieved by flux-coupling a superconducting LC loop to a current-biased feedline; the resulting screening current leads to a change of the kinetic inductance and shift in the resonance frequency. The thin-film aluminum resonator consists of an interdigitated capacitor and thin line inductors forming a closed superconducting loop. The magnetic flux from the nearby niobium current feedline induces Meissner shielding currents in the resonator loop leading to a change in the kinetic part of the total inductance of the resonator. We demonstrate continuous frequency tuning within 160 MHz around the resonant frequency of 2.7 GHz. We show that: (1) frequency up-conversion is achieved when a kilohertz ac modulation signal is superimposed onto the dc bias resulting in sidebands to the resonator tone; (2) three-wave mixing is attained by parametrically pumping the nonlinear kinetic inductance using a strong rf pump signal in the feedline. The simple architecture is amenable to large-array multiplexing and on-chip integration with other circuit components. The concept could be applied in flux magnetometers, up-converters, and parametric amplifiers operating above 4 K when alternative high-critical-temperature material with high kinetic inductance is used.
In this licentiate thesis design, fabrication, and measurements of tunable superconducting microwave transmission line resonators are described. The resonators are of quarter wavelength type were the tuning is achieved by changing one of the boundary conditions of the resonator through a tunable impedance. As tunable impedance the Josephson inductance in form of SQUIDs is used. The Josephson inductance can then be tuned by applying a magnetic field to the SQUID loop. A tuning range of 750 MHz for a 5 GHz resonator is achieved, and as a figure of merit it can be tuned over 200 line widths. The purpose of the tunable resonators is to use them for dynamic coupling of superconducting quantum bits, this requires that the resonators can be tuned fast on the timescale of the resonator-qubit coupling. To measure tuning speeds faster then the ring up time of the resonators a method that measures the leakage of energy out of a detuned resonator was developed. With this method a frequency shift of the energy stored in the resonator can be measured. A detuning of 330 MHz in less than 10 ns is demonstrated for a 4.5 GHz resonator with a quality factor of 104^44. Working in the few photon limit indicates that the devices can be used to change the frequency of individual photons, this is however still to be demonstrated. As a part of this work the dressed states of a superconducting charge qubit was also studied.