fix: Statevector.to_dict(decimals= 3) does not round results and ignores the decimals keyword (Qiskit#12113)

* fix: `SparsePauliOp.to_dict(decimals= 3)` does not return rounded results

* test: add `test_to_dict_decimals`

* add release note

* refactor: release note and test

* style(lint): formatted with black

---------

Co-authored-by: Shelly Garion <46566946+ShellyGarion@users.noreply.github.com>

Author: e-zz

qiskit/quantum_info/states/quantum_state.py

@@ -400,7 +400,7 @@ def _vector_to_dict(vec, dims, decimals=None, string_labels=False):
 
         # Make dict of tuples
         if string_labels:
-            return dict(zip(kets, vec[inds]))
+            return dict(zip(kets, vals[inds]))
 
         return {tuple(ket): val for ket, val in zip(kets, vals[inds])}
 

releasenotes/notes/fix_to_dict_decimals-2f0d3bb865fb09a9.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    The method :meth:`.Statevector.to_dict` will now respect its ``decimals`` keyword argument, which it previously ignored.  

test/python/quantum_info/states/test_statevector.py

@@ -486,6 +486,14 @@ def test_to_dict(self):
                     target[key] = 2 * i + j + 1
             self.assertDictAlmostEqual(target, vec.to_dict())
 
+    def test_to_dict_decimals(self):
+        """Test to_dict method with decimals argument."""
+        decimal = 3
+        sv = np.array([1 / np.sqrt(2), 0, 0, -1 / np.sqrt(2)], dtype=np.complex128)
+        vec_rounded = Statevector(sv).to_dict(decimals=decimal)
+        expected = {"00": 0.707, "11": -0.707}
+        self.assertEqual(vec_rounded, expected)
+
     def test_probabilities_product(self):
         """Test probabilities method for product state"""