Get a dictionary of two-qubit Bell state fidelities (normalized to unity)
        from the specs, keyed by targets (qubit-qubit pairs).

        :return: A dictionary of Bell state fidelities, normalized to unity.
        :rtype: Dict[tuple(int, int), float]

def fBellStates(self):
        """
        Get a dictionary of two-qubit Bell state fidelities (normalized to unity)
        from the specs, keyed by targets (qubit-qubit pairs).

        :return: A dictionary of Bell state fidelities, normalized to unity.
        :rtype: Dict[tuple(int, int), float]
        """
        return {tuple(es.targets): es.fBellState for es in self.edges_specs}