Consistent sparse list format in sparse operators (#14067)

* Consistent sparse list format in sparse operators

* review comments

- use combine in test
- fix comment

Author: Cryoris

crates/accelerate/src/sparse_observable/mod.rs

@@ -2931,14 +2931,11 @@ impl PySparseObservable {
         let to_py_tuple = |view: SparseTermView| {
             let mut pauli_string = String::with_capacity(view.bit_terms.len());
 
-            // we reverse the order of bits and indices so the Pauli string comes out in
-            // "reading order", consistent with how one would write the label in
-            // SparseObservable.from_list or .from_label
-            for bit in view.bit_terms.iter().rev() {
+            for bit in view.bit_terms.iter() {
                 pauli_string.push_str(bit.py_label());
             }
             let py_string = PyString::new(py, &pauli_string).unbind();
-            let py_indices = PyList::new(py, view.indices.iter().rev())?.unbind();
+            let py_indices = PyList::new(py, view.indices.iter())?.unbind();
             let py_coeff = view.coeff.into_py_any(py)?;
 
             PyTuple::new(py, vec![py_string.as_any(), py_indices.as_any(), &py_coeff])

test/python/circuit/library/test_evolution_gate.py

@@ -27,7 +27,7 @@
 from qiskit.converters import circuit_to_dag
 from qiskit.quantum_info import Operator, SparsePauliOp, Pauli, Statevector, SparseObservable
 from qiskit.transpiler.passes import HLSConfig, HighLevelSynthesis
-from test import QiskitTestCase  # pylint: disable=wrong-import-order
+from test import QiskitTestCase, combine  # pylint: disable=wrong-import-order
 
 X = SparsePauliOp("X")
 Y = SparsePauliOp("Y")
@@ -316,11 +316,10 @@ def test_dag_conversion(self):
 
         self.assertEqual(ops, expected_ops)
 
-    @data("chain", "fountain")
-    def test_cnot_chain_options(self, option):
+    @combine(option=["chain", "fountain"], use_sparse_observable=[True, False])
+    def test_cnot_chain_options(self, option, use_sparse_observable):
         """Test selecting different kinds of CNOT chains."""
-
-        op = Z ^ Z ^ Z
+        op = SparseObservable("ZZZ") if use_sparse_observable else SparsePauliOp(["ZZZ"])
         synthesis = LieTrotter(reps=1, cx_structure=option)
         evo = PauliEvolutionGate(op, synthesis=synthesis)
 
@@ -595,7 +594,7 @@ def test_projector_circuit(self):
             -1 +1 +1 -1 -1 +1  // eigenvalue
              1  0  0  1  1  0  // ctrl state
             -----------------
-            --> P(-1).ctrl_state(00110) applied on qubits [0, 1, 2, 3, 4, 5]
+            --> [X P(-1) X].ctrl_state(11001) applied on qubits [5, 4, 3, 2, 1, 0]
 
         """
         op = SparseObservable("-+rl10")
@@ -605,7 +604,9 @@ def test_projector_circuit(self):
         reference.sx([2, 3])
         reference.h([4, 5])
 
-        reference.append(PhaseGate(-1.0).control(5, ctrl_state="00110"), reference.qubits)
+        reference.x(0)
+        reference.append(PhaseGate(-1.0).control(5, ctrl_state="11001"), reference.qubits[::-1])
+        reference.x(0)
 
         reference.sxdg([2, 3])
         reference.h([4, 5])