CP asymmetry and visible decay in 3 + 1 neutrino oscillations on a quantum computer

This paper investigates how visible neutrino decay—where a heavy neutrino mass eigenstate decays into lighter neutrinos and unobserved light scalars—alters the CP asymmetry in muon-to-electron neutrino oscillations. While the decay interaction itself is assumed to preserve CP symmetry, the redistribution of energy and the interference between daughter neutrinos can modify the overall CP-violating signal. The authors model this in a 3+1 neutrino framework (three active plus one sterile neutrino) and use an open quantum system approach to track how parent attenuation and daughter regeneration contribute to the appearance probability.

To validate these theoretical predictions, the researchers implement a quantum simulation on an IBM quantum processor. They construct a five-qubit circuit that maps the decay channel, including parent survival and daughter interference, and use this to measure the regenerated CP contribution. The experiment focuses on an effective two-energy benchmark, allowing for a direct comparison between quantum measurements and classical evolution.

The study finds that visible decay significantly impacts the CP asymmetry, with the regenerated daughter signal contributing roughly 46% of the total decay-induced shift in the reference benchmark. The quantum processor measurements, after correcting for assignment errors, show strong agreement with the theoretical predictions within one standard error. Furthermore, the authors demonstrate that the regenerated CP signal is suppressed when daughter coherence or CP-sensitive mixing factors vanish, confirming the physical requirements for the observed asymmetry.

As neutrino experiments reach higher precision, understanding the subtle effects of non-standard physics like neutrino decay becomes essential for interpreting oscillation data. This work demonstrates that quantum computers can effectively simulate these open-system dynamics, providing a scalable alternative to classical methods for modeling complex neutrino interactions. By isolating the roles of coherence and regeneration, the study provides a clear framework for incorporating decay effects into future neutrino oscillation analyses.