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High kinetic inductance superconducting nanowires


Joint efforts involving two teams from the LPS have demonstrated that beam-assisted deposition of superconducting materials with a He-based focused ion beam (He-FIB) can be used to design and deposit superconducting nano-objects with a versatile direct write process. In particular, nanowires could be made very thin (5nm), narrow (35nm) and long (400µm), demonstrating a very high kinetic inductance, 250 times larger than the geometrical one.

This technological breakthrough was made possible by the unique properties and stability of a recently acquired helium focused ion beam machine. These nanowires hold a great promise for superconducting circuits applications.

High kinetic inductance superconducting materials have a growing impact in the superconducting circuits community. Operated in the microwave frequency domain, they allow to engineer high impedance circuits which have been shown to provide an efficient way to increase the lifetime of superconducting quantum bits or couple electron charge and spins to microwave photons.

Until now, these materials consisted of arrays of Josephson junctions, disordered thin films of metallic compounds (NbN, TiN…), granular aluminum, or superconducting semiconductors. Their use in superconducting circuits usually requires a final sharpening step using electron-beam lithography which has so far reduced their range of application.

In this work, researchers from LPS have pioneered a novel type of hybrid microwave resonator where the inductive part is set by a superconducting tungsten nanowire made by helium beam assisted deposition. Thanks to the large kinetic inductance of the nanowire, the resonator was nonlinear (120 Hz/photon) and had a reasonably high quality factor (4000).

(a) Scanning electron micrograph of three coplanar waveguide resonators coupled to a microwave transmission line. (b) A typical tungsten nanowire deposited with the He-FIB acting as a microwave resonator. (c) Temperature dependence of the microwave transmission spectra. The large resonance frequency shift is typical of large kinetic inductance resonators.

Reference

High kinetic inductance microwave resonators made by He-Beam assisted deposition of tungsten nanowires
J. Basset, D. Watfa, G. Aiello, M. Féchant, A. Morvan, J. Estève, J. Gabelli, M. Aprili, R. Weil, A. Kasumov, H. Bouchiat, R. Deblock
Appl. Phys. Lett. 114, 102601 (2019)
doi:10.1063/1.5080925

Contact

Julien Basset