  We have previously studied the time-dependence of a B anti B meson mixture in
terms of its density matrix. The requirement that the absolute value of the
Stokes vector zeta(t) should evolve monotonically from its initial value
zeta(0)=0 to its final value zeta(infinity)=1 was shown to lead to an upper
bound on the CP violating overlap <B_L|B_S>. In the present note we consider an
entropy variable S as an alternative measure of mixing. We show that exactly
the same upper bound emerges from the requirement that the flow of entropy is
unidirectional (dS/dt<0). We compare the entropic current dS/dt with and
without CP violation and identify certain physical features that appear when
the bound on <B_L|B_S> is violated.
