DC Noise Measurement on Josephson Junctions

Understanding microscopic noise sources such as two-level system (TLS) defects in materials is crucial for improving coherence in superconducting qubits and quantum circuits. Some of these TLS defects are believed to reside in the oxide barrier of the junction, where they contribute to low-frequency noise and dissipation. We present low-frequency noise measurements on single Josephson junctions(JJs) using a cross-correlation technique to suppress intrinsic amplifier noise. The Al-AlOx-Al Josephson junctions were fabricated in-house using the standard Dolan bridge double-angle evaporation technique, with an area of approximately 100 nm × 100 nm. The cross-correlation method enables sub-nanovolt sensitivity by rejecting uncorrelated noise sources, providing direct access to the junction’s intrinsic fluctuation spectrum. We are developing the cross-correlated noise measurement as a powerful probe of TLS-induced noise and decoherence mechanisms in superconducting devices.