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arXiv:2406.10386 · Physical Review Applied

Magnetic-field-tolerant superconducting spiral resonators for circuit quantum electrodynamics

Mihirangi Medahinne, Yadav P. Kandel, Suraj Thapa Magar, Elizabeth Champion, John M. Nichol, Machiel Blok

Published Jan 28, 2025• 6 citations
arXivHTMLPDF

Abstract

We present thin-film niobium ($\mathrm{Nb}$) spiral resonators exhibiting large geometric inductance, high critical magnetic fields, and high single-photon quality factors. These low-loss geometric inductors can be a compelling alternative to kinetic inductors to create high-impedance superconducting devices for applications that require magnetic fields. By varying the spiral pitch, we realize resonators with characteristic impedances ranging from $3.25--7.09\phantom{\rule{0.2em}{0ex}}\mathrm{k}\mathrm{\ensuremath{\Omega}}$. We measure the temperature and magnetic-field-dependent losses and find that the high-impedance resonators maintain an intrinsic quality factor above approximately ${10}^{5}$ for parallel magnetic fields of up to 1 T. These properties make spiral $\mathrm{Nb}$ resonators a promising candidate for quantum devices that require circuit elements with high impedance and magnetic-field resilience.

DOI
10.1103/physrevapplied.23.014070

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We present thin-film niobium (Nb\mathrm{Nb}Nb) spiral resonators exhibiting large geometric inductance, high critical magnetic fields, and high single-photon quality factors. These low-loss geometric inductors can be a compelling alternative to kinetic inductors to create high-impedance superconducting devices for applications that require magnetic fields. By varying the spiral pitch, we realize resonators with characteristic impedances ranging from 3.25−−7.09k\ensuremathΩ3.25--7.09\phantom{\rule{0.2em}{0ex}}\mathrm{k}\mathrm{\ensuremath{\Omega}}3.25−−7.09k\ensuremathΩ. We measure the temperature and magnetic-field-dependent losses and find that the high-impedance resonators maintain an intrinsic quality factor above approximately 105{10}^{5}105 for parallel magnetic fields of up to 1 T. These properties make spiral Nb\mathrm{Nb}Nb resonators a promising candidate for quantum devices that require circuit elements with high impedance and magnetic-field resilience.
We characterize niobium nitride (NbN) λ/2 coplanar waveguide resonators, which were fabricated from a 10-nm-thick film on silicon dioxide grown by sputter deposition. For films grown at 180 °C, we report a superconducting critical temperature of 7.4 K associated with a normal square resistance of 1 kΩ, leading to a kinetic inductance of 192 pH/◻. We fabricated resonators with a characteristic impedance up to 4.1 kΩ and internal quality factors Qi>104 in the single photon regime at zero magnetic field. Moreover, in the many photon regime, the resonators present a high magnetic field resilience with Qi>104 in a 6 T in-plane magnetic field and in a 300 mT out-of-plane magnetic field. These findings make such resonators a compelling choice for circuit quantum electrodynamics experiments involving quantum systems with small electric dipole moments operated in finite magnetic fields.
Niobium nitride (NbN\mathrm{Nb}\mathrm{N}NbN) is a particularly promising material for quantum technology applications, as it shows the degree of reproducibility necessary for large-scale superconducting circuits. We demonstrate that resonators based on NbN\mathrm{Nb}\mathrm{N}NbN thin films present a one-photon internal quality factor above 105{10}^{5}105 maintaining a high impedance (larger than $2\mathrm{k}\mathrm{\ensuremath{\Omega}}$), with a footprint of approximately $50\ifmmode\times\else\texttimes\fi{}100\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{m}}^{2}$ and a Kerr nonlinearity of few tenths of a hertz. These quality factors, mostly limited by losses induced by the coupling to two-level systems, have been maintained for kinetic inductances ranging from tenths to hundreds of picoHenry per square. We also demonstrate minimal variations in the performance of the resonators during multiple cooldowns over more than nine months. Our work proves the versatility of niobium nitride high-kinetic-inductance resonators, opening perspectives towards the fabrication of compact, high-impedance, and high-quality multimode circuits, with sizable interactions.
Superconducting spiral inductors are emerging as key components for radio-frequency (RF) reflectometry, a widely used readout technique for semiconductor spin qubits. Future scalable quantum-computing architectures are expected to operate at elevated temperatures and magnetic fields, placing new demands on the performance and stability of superconducting circuit elements. Here, we present a systematic study of NbTiN spiral inductors under temperatures of several kelvin and magnetic fields approaching 1 T. By combining weakly coupled resonator measurements with independent two-port inductance extraction, we separate inductive and capacitive contributions to device behaviour and directly identify the origin of resonance shifts and quality factor degradation. Furthermore, we establish practical design metrics linking geometry, temperature sensitivity, and magnetic-field robustness. These results provide a general framework for benchmarking superconducting inductors and guiding the design of future RF-reflectometry circuits for practical quantum technologies.
Superconducting resonators with high-kinetic inductance play a central role in hybrid quantum circuits, enabling strong coupling with quantum systems with small electric dipole moment and improved parametric amplification. However, optimizing these resonators simultaneously for high internal quality factors (QiQ_iQi​) and resilience to strong magnetic fields remains challenging. In this study, we systematically compare superconducting resonators fabricated from niobium nitride (NbN) and granular aluminum (grAl) thin films, each having similar kinetic inductance values (Lk∼100L_k \sim 100Lk​∼100 pH/sq). At zero magnetic field, resonators made from grAl exhibit higher QiQ_iQi​ compared to their NbN counterparts. However, under applied magnetic fields, NbN resonators demonstrate significantly better resilience. Moreover, NbN resonators exhibit an unexpected increase in QiQ_iQi​ at intermediate in-plane magnetic fields (B∥∼1B_{\parallel} \sim 1B∥​∼1 T), which we attribute to an enhanced frequency detuning that reduce coupling to two-level system defects. In contrast, grAl resonators show a distinct critical field above which QiQ_iQi​ rapidly decreases, strongly depending on resonator cross-section respect to the applied field direction. Characterization of the nonlinear properties at zero magnetic field reveals that the self-Kerr coefficient in grAl resonators is more than an order of magnitude higher than in NbN resonators, making grAl particularly attractive for applications requiring pronounced nonlinear interactions. Our findings illustrate a clear trade-off between the two materials: NbN offers superior magnetic-field resilience beneficial for hybrid circuit quantum electrodynamics applications, while grAl is more advantageous in low-field regimes demanding high impedance and strong nonlinearity.
A15 superconductors are distinguished by their high critical temperatures, magnetic fields, and current-carrying capabilities. Among them, Nb3_33​Al is of particular interest for superconducting quantum circuits as a means to extend device operating temperatures, provided that its electrodynamic properties are well understood. Here, we report on the synthesis of Nb3_33​Al thin films by magnetron co-sputtering followed by rapid thermal processing, yielding superconducting transition temperatures above 16~K. Microwire devices patterned from these films exhibit a coherence length of 3.2 nm3.2\,\mathrm{nm}3.2nm and superfluid densities as low as 1.1×1026 m−31.1\times 10^{26}\,\mathrm{m}^{-3}1.1×1026m−3, suggesting that Nb3_33​Al may enable high kinetic inductance in thinner films. Coplanar waveguide resonators fabricated on Nb3_33​Al demonstrate single-photon internal quality factors up to 2.26×1052.26\times 10^{5}2.26×105. These results establish Nb3_33​Al as a promising material platform for the development of superconducting quantum circuits operating at elevated temperatures, contingent on appropriate control of interfacial chemistry and surface morphology.
We demonstrate a planar superconducting microwave resonator intended for use in applications requiring strong magnetic fields and high quality factors. In perpendicular magnetic fields of 20 mT, the niobium resonators maintain a quality factor above 25 000 over a wide range of applied powers, down to single photon population. In parallel field, the same quality factor is observed above 160 mT, the field required for coupling to free spins at a typical operating frequency of 5 GHz. We attribute the increased performance to the current branching in the fractal design. We demonstrate that our device can be used for spectroscopy by measuring the dissipation from a pico-mole of molecular spins.