Granular Aluminum – A Versatile Material for Superconducting Detectors and Quantum Circuits
Granular aluminum (grAl) is an intriguing superconducting material, which has been receiving increasing attention in the superconducting quantum bits (qubits) and detectors communities. Among its key features are a tunable kinetic inductance up to nH/sq, amenable nonlinearity, and low microwave frequency losses [1,2,3]. Furthermore, quasiparticle relaxation times on the order of ~s have been observed [1]. In elucidating the sources of excess quasiparticles, the role of ionizing radiation has recently come to the forefront, and abatement of quasiparticle bursts remains an open challenge [4]. Besides showcasing the key features of grAl, we will present our results on a fluxonium qubit, where granular aluminum strips realize a so-called superinductor with an inductance of 225 nH at an impedance > 6.6 kΩ [5]. We will also discuss a transmon-type qubit in which a grAl volume of 10-3 μm3 realizes the non-linearity [6]. Thanks to their impedance in the kΩ range, grAl strips also play an important role in providing the high-impedance environment for the measurement of Bloch-oscillations, the dual of Shapiro steps – potentially enabling a current standard traceable to fundamental constants.
[1] L. Grünhaupt et. al., Phys. Rev. Lett. 121, 117001 (2018)
[2] N. Maleeva et al., Nat. Commun. 9, 3889 (2018)
[3] F. Valenti et al., Phys. Rev. Applied 11, 054087 (2019)
[4] L. Cardani & F. Valenti et al., Nat. Commun. 12, 2733 (2021)
[5] L. Grünhaupt & M. Spiecker et al., Nature Mat. 18, 816-819 (2019)
[6] P. Winkel et al., Phys. Rev. X 10, 031032 (2020)
Granular aluminum (grAl) is an intriguing superconducting material, which has been receiving increasing attention in the superconducting quantum bits (qubits) and detectors communities. Among its key features are a tunable kinetic inductance up to nH/sq, amenable nonlinearity, and low microwave frequency losses [1,2,3]. Furthermore, quasiparticle relaxation times on the order of ~s have been observed [1]. In elucidating the sources of excess quasiparticles, the role of ionizing radiation has recently come to the forefront, and abatement of quasiparticle bursts remains an open challenge [4]. Besides showcasing the key features of grAl, we will present our results on a fluxonium qubit, where granular aluminum strips realize a so-called superinductor with an inductance of 225 nH at an impedance > 6.6 kΩ [5]. We will also discuss a transmon-type qubit in which