diff --git a/src/framework/circuit.hpp b/src/framework/circuit.hpp
index fa4a046aa9..9194852d17 100644
--- a/src/framework/circuit.hpp
+++ b/src/framework/circuit.hpp
@@ -596,14 +596,10 @@ void Circuit::set_params(bool truncation) {
       // truncate save_expval here when remap is not needed
       if (ops[pos].type == OpType::save_expval ||
           ops[pos].type == OpType::save_expval_var) {
-        int_t nparams = ops[pos].string_params.size();
+        int_t nparams = ops[pos].expval_params.size();
         for (int_t i = 0; i < nparams; i++) {
-          // save original pauli string to restore for output
-          ops[pos].string_params.push_back(ops[pos].string_params[i]);
-
-          ops[pos].string_params[i].assign(ops[pos].string_params[i].end() -
-                                               qubitmap_.size(),
-                                           ops[pos].string_params[i].end());
+          std::string &pauli = std::get<0>(ops[pos].expval_params[i]);
+          pauli.assign(pauli.end() - qubitmap_.size(), pauli.end());
         }
         ops[pos].qubits.resize(qubitmap_.size());
       }
@@ -673,19 +669,16 @@ void Circuit::set_params(bool truncation) {
 void Circuit::remap_qubits(Op &op) const {
   // truncate save_expval
   if (op.type == OpType::save_expval || op.type == OpType::save_expval_var) {
-    int_t nparams = op.string_params.size();
+    int_t nparams = op.expval_params.size();
     for (int_t i = 0; i < nparams; i++) {
-      uint_t size = op.string_params[i].length();
-      // save original pauli string to restore for output
-      op.string_params.push_back(op.string_params[i]);
+      std::string &pauli = std::get<0>(op.expval_params[i]);
       std::string new_pauli;
       new_pauli.resize(qubitmap_.size());
-
       for (auto q = qubitmap_.cbegin(); q != qubitmap_.cend(); q++) {
         new_pauli[qubitmap_.size() - 1 - q->second] =
-            op.string_params[i][size - 1 - q->first];
+            pauli[pauli.size() - 1 - q->first];
       }
-      op.string_params[i] = std::move(new_pauli);
+      pauli = new_pauli;
     }
     for (int_t i = 0; i < qubitmap_.size(); i++) {
       op.qubits[i] = i;
diff --git a/src/simulators/extended_stabilizer/extended_stabilizer_state.hpp b/src/simulators/extended_stabilizer/extended_stabilizer_state.hpp
index bc5831db45..9fec5d1656 100644
--- a/src/simulators/extended_stabilizer/extended_stabilizer_state.hpp
+++ b/src/simulators/extended_stabilizer/extended_stabilizer_state.hpp
@@ -803,17 +803,14 @@ void State::apply_save_expval(const Operations::Op &op,
       sq_expval += std::get<2>(param) * val;
     }
   }
-  int_t key = 0;
-  if (op.string_params.size() > 1)
-    key = 1;
   if (variance) {
     std::vector<double> expval_var(2);
     expval_var[0] = expval;                      // mean
     expval_var[1] = sq_expval - expval * expval; // variance
-    result.save_data_average(creg(), op.string_params[key], expval_var, op.type,
+    result.save_data_average(creg(), op.string_params[0], expval_var, op.type,
                              op.save_type);
   } else {
-    result.save_data_average(creg(), op.string_params[key], expval, op.type,
+    result.save_data_average(creg(), op.string_params[0], expval, op.type,
                              op.save_type);
   }
 }
diff --git a/src/simulators/state.hpp b/src/simulators/state.hpp
index 645c240b3a..219eaa6bb0 100644
--- a/src/simulators/state.hpp
+++ b/src/simulators/state.hpp
@@ -434,17 +434,14 @@ void Base::apply_save_expval(const Operations::Op &op,
       sq_expval += std::get<2>(param) * val;
     }
   }
-  int_t key = 0;
-  if (op.string_params.size() > 1)
-    key = 1;
   if (variance) {
     std::vector<double> expval_var(2);
     expval_var[0] = expval;                      // mean
     expval_var[1] = sq_expval - expval * expval; // variance
-    result.save_data_average(creg(), op.string_params[key], expval_var, op.type,
+    result.save_data_average(creg(), op.string_params[0], expval_var, op.type,
                              op.save_type);
   } else {
-    result.save_data_average(creg(), op.string_params[key], expval, op.type,
+    result.save_data_average(creg(), op.string_params[0], expval, op.type,
                              op.save_type);
   }
 }