Quantum spread complexity as a probe of NSI, $CP$ Violation, and mass ordering in neutrino oscillations in matter

Abstract

Quantum spread complexity characterizes how a quantum state evolves and becomes distributed over the Hilbert space under unitary dynamics. In this work, we employ a cost function as a quantitative measure of spread complexity. We investigate this cost function within the framework of three-flavor neutrino oscillations in vacuum and matter, incorporating the $CP$-violation phase and Non-Standard Interaction (NSI) effects, under both normal and inverted mass ordering scenarios. The cost function is evaluated for each scenario and analyzed with the corresponding neutrino transition probabilities for both initial muon neutrino and muon antineutrino flavor states. The results are presented using the energy where the first oscillation is maximum and baseline lengths of ongoing long-baseline accelerator neutrino experiments, including T2K and NOvA, as well as upcoming experiments such as DUNE and P2O. Our findings indicate that the difference in the cost function between normal and inverted mass orderings during neutrino propagation in matter is sensitive to these experiments, with the appropriate choice of NSI parameters and the best-fit $CP$-violation phase values.