  Nambu Quantum Mechanics, proposed in Phys. Lett. B536, 305 (2002), is a
deformation of canonical Quantum Mechanics in which only the time-evolution of
the "phases" of energy eigenstates is modified. We discuss the effect this
theory will have on oscillation phenomena, and place a bound on the deformation
parameters utilizing the data on the atmospheric neutrino mixing angle
$\theta_{23}$.
