'op will operate on each individual state.
Parameters
op : Operator
Examples
>>> from sympy.physics.quantum.state import Ket
>>> from sympy.physics.quantum.density import Density
>>> from sympy.physics.quantum.operator import Operator
>>> A = Operator(\'A\')
>>> d = Density([Ket(0), 0.5], [Ket(1),0.5])
>>> d.apply_op(A)
\'Density\'((A*|0>, 0.5),(A*|1>, 0.5))'

def apply_op(self, op):

    new_args = [((op * state), prob) for (state, prob) in self.args]
    return Density(*new_args)
