Infrared Reduction and Structural Classification \\of Flux Noise in Superconducting Qubits

Low-frequency 1/f flux noise is a dominant decoherence mechanism in superconducting qubits, yet its characterization often relies on phenomenological fits that may introduce unnecessary infrared parameters. We formulate an infrared reduction theorem stating that, within a frequency window where the noise power spectral density (PSD) exhibits a single dominant algebraic asymptotic of the form S(omega) = A omega^s plus smaller-order terms, any infrared-local dynamical observable depends on the exponent s alone. In particular, no second independent continuous infrared exponent is representable within this algebraic-local class.We translate this result into an operational protocol based on log–log regression, effective-slope stability, residual diagnostics, and information-criterion model comparison. Applying the protocol to a Bylander-like flux-noise spectrum spanning nearly three decades in frequency, we find a stable single exponent with no statistically supported logarithmic corrections or second comparable exponent. The data are therefore consistent with the algebraic-local infrared class.Our results do not introduce a new microscopic model of flux noise; rather, they establish a structural reduction principle that prevents infrared overparameterization and provides a falsifiable criterion for detecting changes of dynamical regime in superconducting qubits.