Testing Colored-Noise Collapse Models with Superfluid Helium-4

Dynamical collapse models such as Continuous Spontaneous Localization (CSL) address the quantum measurement problem and predict a tiny spontaneous heating of matter. The originally proposed parameter range of white-noise CSL has been excluded by X-ray searches, most recently XENONnT (2026). These X-ray bounds, however, lose their validity if the collapse noise is "colored", i.e. cut off below X-ray frequencies. In that regime the strongest remaining constraints come from bulk heating of solids and from low-frequency mechanical experiments. This feasibility study applies the colored-noise heating formalism of Adler and Vinante to superfluid helium-4. Because the sound speed of helium (~238 m/s) is about 17 times lower than that of solids, helium samples the noise spectrum at correspondingly lower frequencies. This gives a sensitivity advantage over solids of ~280 for Lorentzian (cCSL) noise and up to ~10^6 for a sharp cutoff. For r_C = 10^-7 m, a helium calorimeter limiting unexplained heating to 10 pW/kg (1 pW/kg) would improve on the strongest existing bound by a factor of ~2 (~25) in the window Ω ≈ 3×10^9 – 5×10^10 s^-1. This window overlaps with cosmologically motivated cutoff frequencies for cCSL. The note includes closed-form results, validated numerical calculations, and a proposed experimental concept: underground DC calorimetry with tens of kilograms of superfluid helium, using a fill-level differential measurement to separate wall-induced backgrounds. Limitations and open questions are discussed.