  The Bitter-Dubbers (BD) experiment is an important experiment that originally
aimed to measure topological phase using polarized-neutron spin rotation in a
helical magnetic field under adiabatic conditions. Contrary to expectations,
upon reevaluation of the BD experiment, it has been found that adiabatic
conditions are not necessary for measuring topological phase. In scenarios
where the magnetic field is neither homogeneous nor strong enough, and the
neutron has a fast velocity, the topological phase can still be manifested. To
demonstrate this, we analytically solve the time-dependent Schrodinger equation
for the neutron spin rotation in general rotating systems. These exact
solutions are then utilized to investigate the nonadiabatic topological phase
under the conditions mentioned above. The numerical simulations of the
nonadiabatic topological phase have shown a strong concurrence with the BD
experimental data. This novel result extends our understanding of the
topological phase observed in neutron spin rotation, even in more complex and
dynamic scenarios beyond the originally required adiabatic conditions.
