Kinetic-inductance-incorporated quantization for accurate Hamiltonian prediction in superconducting circuits

We propose an improved method for quantizing superconducting circuits that incorporates material- and geometry-dependent kinetic inductance. Our approach models thin superconducting films as equivalent reactive boundary elements, seamlessly integrating into the conventional circuit quantization framework without adding significant computational complexity. As a proof of concept, we experimentally verify our method using planar superconducting quantum devices made of 35-nm-thick disordered niobium films, known to exhibit large kinetic inductance values. We demonstrate significantly improved accuracy in predicting the Hamiltonian based solely on the chip layout and material properties of superconducting films and Josephson junctions. Specifically, conventional methods exhibit average errors of 5.4% in mode frequencies and 41% in cross-Kerr shift frequencies, while our method reduces the errors to 1.1% and 11%, respectively. Our method enables systematic studies of superconducting devices based on disordered thin films or compact, fine-pitched elements and, more broadly, facilitates the precise engineering of superconducting quantum circuits at scale.