def _superoperator_(self) -> np.ndarray:
        """Returns superoperator representation of self if possible, else `NotImplemented`."""
        if not self._has_superoperator_():
            return NotImplemented
        return qis.kraus_to_superoperator(self._kraus_())
Returns superoperator representation of self if possible, else `NotImplemented`.
cirq-core/cirq/circuits/moment.py