Low loss lumped-element inductors made from granular aluminum: part 1

Linear inductors are a key component in superconducting quantum circuits. However, it is challenging to build inductors that are simultaneously compact, linear and low-loss with standard approaches that either rely on the geometric inductance of superconducting thin films or on the kinetic inductance of Josephson junction arrays. Granular Aluminum (grAl) films are a promising alternative for realizing such inductors. Before grAl inductors can be used in state-of-the-art superconducting circuits, it is important to understand loss mechanisms associated with grAl films and develop techniques for integrating them with other materials. In part 1 of this talk, we first present results on lumped-element all-grAl resonators with 4 - 12 nH of inductance. We demonstrate single photon quality factors > 2 million, surpassing previously reported values for grAl resonators by almost an order of magnitude. Further, we demonstrate an ex-situ method to combine grAl with other superconductors, such as aluminum and tantalum. We show that hybrid resonators built using this method can achieve high quality factors of over 10⁶. Finally, from our detailed loss analysis combining all samples, we identify the dominant loss mechanism limiting these grAl inductors.