On-Chip Bandpass Filter for Superconducting Devices

Abstract

On-chip lumped element bandpass filters offer a pathway to tightly integrate noise suppression directly at the chip level in superconducting quantum devices. Despite the widespread use of filters in cryogenic qubit setups, co-fabricated lumped element bandpass filters remain relatively unexplored. This work evaluates their feasibility, design constraints, and performance when embedded directly on a superconducting qubit chip, paving the way for scalable quantum architectures. The filter design follows a standard radio frequency (RF) synthesis approach, adapted to cryogenic operation, co-fabrication constraints, limited footprint, and superconducting drive requirements. A scalable design flow is developed to implement arbitrary-order bandpass filters using lumped inductors and capacitors. Electromagnetic (EM) simulations are employed to extract effective component parameters and refine circuit models beyond ideal lumped element approximations. Simulations show that on-chip lumped element bandpass filters can achieve welldefined passband characteristics and support higher-order architectures. However, ideal and extended lumped element models alone are insufficient to predict device response accurately. Direct optimization with computationally intensive EM simulations were therefore necessary to achieve reliable filter performance. The filter response also directly influences the thermal noise spectrum experienced by the qubit. Modeling indicates that appropriately designed bandpass filters can reduce unwanted thermal occupation, providing a tool for engineering and investigating the qubit’s EM environment. A prototype device was fabricated and characterized at cryogenic temperatures. The measured response did not exhibit the intended passband, with analysis pointing to fabrication issues, particularly unreliable capacitor connections, rather than limitations of the filter concept or design methodology. Overall, this work establishes a simulation-driven platform for co-fabricated lumped element bandpass filters in superconducting quantum circuits. The results demonstrate their feasibility, scalability, and potential for controlled thermal noise engineering in cryogenic quantum hardware.