Update mode_based_mapper.py

qiskit_nature/second_q/mappers/mode_based_mapper.py

@@ -61,7 +61,7 @@ def sparse_pauli_operators(
         # pylint: disable=unused-argument
         """Generates the :class:`.SparsePauliOp` terms.
 
-        This uses :meth:`.QubitMapper.pauli_table` to construct a list of operators used to
+        This uses :meth:`.pauli_table` to construct a list of operators used to
         translate the second-quantization symbols into qubit operators.
 
         Args:
@@ -113,22 +113,21 @@ def mode_based_mapping(
             register_length = second_q_op.register_length
 
         times_creation_op, times_annihilation_op = self.sparse_pauli_operators(register_length)
+        mapped_string_length = times_creation_op[0].num_qubits
 
         # make sure ret_op_list is not empty by including a zero op
-        ret_op_list = [SparsePauliOp("I" * register_length, coeffs=[0])]
+        ret_op_list = [SparsePauliOp("I" * mapped_string_length, coeffs=[0])]
 
         for terms, coeff in second_q_op.terms():
             # 1. Initialize an operator list with the identity scaled by the `coeff`
-            ret_op = SparsePauliOp("I" * register_length, coeffs=np.array([coeff]))
+            ret_op = SparsePauliOp("I" * mapped_string_length, coeffs=np.array([coeff]))
 
             # Go through the label and replace the fermion operators by their qubit-equivalent, then
             # save the respective Pauli string in the pauli_str list.
             for term in terms:
                 char = term[0]
-                if char == "":
-                    break
                 position = int(term[1])
-                if char == "+":
+                if char in ("+", ""):  # "" for MajoranaOp, creator = annihilator
                     ret_op = ret_op.compose(times_creation_op[position], front=True).simplify()
                 elif char == "-":
                     ret_op = ret_op.compose(times_annihilation_op[position], front=True).simplify()