code: def fBellStates(self):
          
          return {tuple(es.targets): es.fBellState for es in self.edges_specs}
docs: 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]