Granular aluminium as a superconducting material for high-impedance quantum circuits

Lukas Grünhaupt; Martin Spiecker; Daria Gusenkova; Nataliya Maleeva; Sebastian T Skacel; Ivan Takmakov; Francesco Valenti; Patrick Winkel; Hannes Rotzinger; Wolfgang Wernsdorfer; Alexey V Ustinov; Ioan M Pop

doi:10.1038/s41563-019-0350-3

Granular aluminium as a superconducting material for high-impedance quantum circuits

Nat Mater. 2019 Aug;18(8):816-819. doi: 10.1038/s41563-019-0350-3. Epub 2019 Apr 29.

Authors

Lukas Grünhaupt^#¹, Martin Spiecker^#¹, Daria Gusenkova¹, Nataliya Maleeva¹, Sebastian T Skacel^{1

2}, Ivan Takmakov^{1

2

3}, Francesco Valenti^{1

4}, Patrick Winkel¹, Hannes Rotzinger¹, Wolfgang Wernsdorfer^{1

2}, Alexey V Ustinov^{1

3}, Ioan M Pop^{5

6}

Affiliations

¹ Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, Germany.
² Institute of Nanotechnology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany.
³ Russian Quantum Center, National University of Science and Technology MISIS, Moscow, Russia.
⁴ Institute for Data Processing and Electronics, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany.
⁵ Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, Germany. ioan.pop@kit.edu.
⁶ Institute of Nanotechnology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany. ioan.pop@kit.edu.

^# Contributed equally.

PMID: 31036961
DOI: 10.1038/s41563-019-0350-3

Abstract

Superconducting quantum information processing machines are predominantly based on microwave circuits with relatively low characteristic impedance, about 100 Ω, and small anharmonicity, which can limit their coherence and logic gate fidelity^1,2. A promising alternative is circuits based on so-called superinductors^3-6, with characteristic impedances exceeding the resistance quantum R_Q = 6.4 kΩ. However, previous implementations of superinductors, consisting of mesoscopic Josephson junction arrays^7,8, can introduce unintended nonlinearity or parasitic resonant modes in the qubit vicinity, degrading its coherence. Here, we present a fluxonium qubit design based on a granular aluminium superinductor strip^9-11. We show that granular aluminium can form an effective junction array with high kinetic inductance and be in situ integrated with standard aluminium circuit processing. The measured qubit coherence time [Formula: see text] illustrates the potential of granular aluminium for applications ranging from protected qubit designs to quantum-limited amplifiers and detectors.