Enhancing Signal Purity in Josephson Structure Measurements

Abstract

Superconducting Josephson structures play a significant role in quantum-state engineering. Achieving high-fidelity quantum state measurements in superconducting Josephson structures requires ultra-low noise environments and robust signal purification techniques. Here, the advanced low-noise signal measurement system designed for dilution refrigerators is presented, integrating multi-stage cryogenic filtering and electromagnetic shielding strategies to suppress noise sources across a broad frequency spectrum. The effectiveness of low-pass RC filters is demonstrated, silver-epoxy microwave absorbers, and optimized ground isolation to achieve an unprecedented noise reduction, enabling sub-nanoampere switching current distribution measurements superior to commerical systems at mK temperatures. The system is optimized for precision studies of superconductor-insulator-superconductor, superconductor-ferromagnet-superconductor, and superconductor-normal metal-superconductor Josephson junctions with low critical currents. This approach establishes a reliable framework for next-generation quantum electronic experiments, ensuring that observed switching phenomena are governed by intrinsic device physics rather than environmental perturbations.