Granular Aluminum – A Versatile Material for Superconducting Detectors and Quantum Circuits

Abstract

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