QPU design and optimization with KQCircuits and open-source simulation tools

KQCircuits is a QPU design tool developed by IQM Quantum Computers, licensed under open-source (GPL-3.0). It provides advanced features for drawing and exporting QPU masks, as well as running simulations in powerful third-party simulators (Ansys, Elmer, Sonnet). In this talk, we showcase the simulation methods utilizing the Elmer open-source multiphysics simulator developed by CSC Finland. Elmer supports high-performance computing platforms, thereby enabling massively parallel simulations and design optimization using fully open-source tools. The current features include 3D full-wave simulations with kinetic inductance, as well as tools for extracting energy participation ratios used for estimating dielectric losses due to two-level systems (TLSs), which have been shown to be one of the dominant coherence-limiting mechanisms in superconducting qubits. We report a T1 value close to 1 ms for a weakly coupled qubit, supported by improved design and fabrication analysis. The experimental results prove the need for accurate modeling and mitigation strategy of TLS losses. KQCircuits has been the tool used to design IQM's quantum processors from 5 to 150 qubits and two-qubit gate fidelities up to 99.9%, while also supporting enthusiasts' designs around the world.