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

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

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

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