Granular aluminium nanojunction fluxonium qubit

Mesoscopic Josephson junctions, consisting of overlapping superconducting electrodes separated by a nanometre-thin oxide layer, provide a precious source of nonlinearity for superconducting quantum circuits. Here we show that in a fluxonium qubit, the role of the Josephson junction can also be playe...

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Bibliographic Details
Published in:Nature materials 2023-02, Vol.22 (2), p.194-199
Main Authors: Rieger, D., Günzler, S., Spiecker, M., Paluch, P., Winkel, P., Hahn, L., Hohmann, J. K., Bacher, A., Wernsdorfer, W., Pop, I. M.
Format: Article
Language:English
Subjects:
639/766/483/2802
639/925/927/1064
Aluminum
Antennas
Biomaterials
Chemistry and Materials Science
Circuits
Condensed Matter Physics
Energy
Evaporation
Josephson junctions
Materials Science
Nanotechnology
Optical and Electronic Materials
Parallel plates
Qubits (quantum computing)
SIS (superconductors)
Spectrum analysis
Superconductivity
Tunnel junctions
Wire
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Summary:Mesoscopic Josephson junctions, consisting of overlapping superconducting electrodes separated by a nanometre-thin oxide layer, provide a precious source of nonlinearity for superconducting quantum circuits. Here we show that in a fluxonium qubit, the role of the Josephson junction can also be played by a lithographically defined, self-structured granular aluminium nanojunction: a superconductor–insulator–superconductor Josephson junction obtained in a single-layer, zero-angle evaporation. The measured spectrum of the resulting qubit, which we nickname gralmonium, is indistinguishable from that of a standard fluxonium. Remarkably, the lack of a mesoscopic parallel plate capacitor gives rise to an intrinsically large granular aluminium nanojunction charging energy in the range of tens of gigahertz, comparable to its Josephson energy. We measure coherence times in the microsecond range and we observe spontaneous jumps of the value of the Josephson energy on timescales from milliseconds to days, which offers a powerful diagnostics tool for microscopic defects in superconducting materials. The authors fabricate a fluxonium circuit using a granular aluminium nanoconstriction to replace the conventional superconductor–insulator–superconductor tunnel junction. Their characterization suggests that this approach will be a useful element in the superconducting qubit toolkit.
ISSN:1476-1122
1476-4660
DOI:10.1038/s41563-022-01417-9