'Returns the operators which this state instance is an eigenstate
of.
This method should be overridden in subclasses. It will be called on
state instances and be passed the operator classes that we wish to make
into instances. The state instance will then transform the classes
appropriately, or raise a NotImplementedError if it cannot return
operator instances. See cartesian.py for examples,'

def _state_to_operators(self, op_classes, **options):

    raise NotImplementedError('Cannot    map    this    state    to    operators.    Method    not    implemented!')
