On-Chip Bandpass Filter for Superconducting Devices

Sammanfattning

On-chip lumped element bandpass filters offer a pathway to tightly integrate noisesuppression directly at the chip level in superconducting quantum devices. Despitethe widespread use of filters in cryogenic qubit setups, co-fabricated lumped elementbandpass filters remain relatively unexplored. This work evaluates their feasibility,design constraints, and performance when embedded directly on a superconductingqubit chip, paving the way for scalable quantum architectures.The filter design follows a standard radio frequency (RF) synthesis approach, adaptedto cryogenic operation, co-fabrication constraints, limited footprint, and superconductingdrive requirements. A scalable design flow is developed to implementarbitrary-order bandpass filters using lumped inductors and capacitors. Electromagnetic(EM) simulations are employed to extract effective component parametersand refine circuit models beyond ideal lumped element approximations.Simulations show that on-chip lumped element bandpass filters can achieve welldefinedpassband characteristics and support higher-order architectures. However,ideal and extended lumped element models alone are insufficient to predict deviceresponse accurately. Direct optimization with computationally intensive EM simulationswere therefore necessary to achieve reliable filter performance.The filter response also directly influences the thermal noise spectrum experiencedby the qubit. Modeling indicates that appropriately designed bandpass filters canreduce unwanted thermal occupation, providing a tool for engineering and investigatingthe 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 pointingto fabrication issues, particularly unreliable capacitor connections, rather thanlimitations of the filter concept or design methodology.Overall, this work establishes a simulation-driven platform for co-fabricated lumpedelement bandpass filters in superconducting quantum circuits. The results demonstratetheir feasibility, scalability, and potential for controlled thermal noise engineeringin cryogenic quantum hardware.