  In a previous publication we noted that the time dependence of an incoherent
$B^0-\bar{B}^0$ mixture undergoes a qualitative change when the magnitude of CP
violation $\delta$ exceeds a critical value. Requiring, on physical grounds,
that the system evolve from an initial incoherent state to a final pure state
in a monotonic way, yields a new upper limit for $\delta$. The recent
measurement of the wrong charge semileptonic asymmetry of $B_s^0$ mesons
presented by the D0 collaboration is outside this bound by one standard
deviation. If this result is confirmed it implies the existence of a new
quantum mechanical oscillation phenomenon.
