Low-loss lumped-element inductors made from granular aluminum
Vishakha Gupta, Patrick Winkel, Neel Thakur +5 more
Lumped-element inductors are an integral component in the circuit QED toolbox. 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. In this work, we overcome this challenge by utilizing the high kinetic inductance offered by superconducting granular aluminum (grAl). We demonstrate lumped-element inductors with a few nH of inductance that are up to 100 times shorter than inductors built from pure aluminum (Al). To characterize the properties of these linear inductors, we first report on the performance of lumped-element resonators built entirely out of grAl with sheet inductances varying from 30 – 320 pH/sq and self-Kerr nonlinearities of 0.2 – 20 Hz / photon . Further, we demonstrate integration of these grAl inductors into hybrid resonators with Al or tantalum ( Ta ) capacitor electrodes without increasing total internal losses. Interestingly, the measured internal quality factors systematically decrease with increasing room-temperature resistivity of the grAl film for all devices, indicating a trade-off between compactness and internal loss. For our lowest resistivity grAl films, we measure quality factors reaching 3.5 × 10 6 for the all-grAl devices and 4.5 × 10 6 for the hybrid grAl/ Ta devices, similar to state-of-the-art quantum circuits. Our loss analysis suggests that the surface-loss factor of grAl is similar to that of pure Al for our lowest resistivity films, while the increasing losses with resistivity could be explained by increasing inductor loss in the grAl film.
arXiv:2411.12611•Physical Review Applied•May 27, 2025•14 citations