From 76f7dffdd50f129706c2065bd48de279eefc6a6d Mon Sep 17 00:00:00 2001
From: Raynel Sanchez <87539502+raynelfss@users.noreply.github.com>
Date: Wed, 11 Dec 2024 12:46:38 -0500
Subject: [PATCH 1/4] Fix: Discard cache when assigning new parameters in
 `CircuitData`.

---
 crates/circuit/src/circuit_data.rs | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/crates/circuit/src/circuit_data.rs b/crates/circuit/src/circuit_data.rs
index 1c12aef9efc..699ad5f3d1c 100644
--- a/crates/circuit/src/circuit_data.rs
+++ b/crates/circuit/src/circuit_data.rs
@@ -1394,13 +1394,7 @@ impl CircuitData {
                                 // Standard gates can all rebuild their definitions, so if the
                                 // cached py_op exists, update the `params` attribute and clear out
                                 // any existing cache.
-                                if let Some(borrowed) = previous.py_op.get() {
-                                    borrowed
-                                        .bind(py)
-                                        .getattr(params_attr)?
-                                        .set_item(parameter, new_param)?;
-                                    borrowed.bind(py).setattr("_definition", py.None())?
-                                }
+                                previous.py_op.take();
                             }
                         } else {
                             // Track user operations we've seen so we can rebind their definitions.

From 0f469899a8345be3d89b7092072e3cc0b8023888 Mon Sep 17 00:00:00 2001
From: Raynel Sanchez <87539502+raynelfss@users.noreply.github.com>
Date: Wed, 11 Dec 2024 13:03:30 -0500
Subject: [PATCH 2/4] Docs: Add release note

---
 .../notes/fix-assign-parameters-ffa284ebde429704.yaml      | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 releasenotes/notes/fix-assign-parameters-ffa284ebde429704.yaml

diff --git a/releasenotes/notes/fix-assign-parameters-ffa284ebde429704.yaml b/releasenotes/notes/fix-assign-parameters-ffa284ebde429704.yaml
new file mode 100644
index 00000000000..b1e1dc5f67d
--- /dev/null
+++ b/releasenotes/notes/fix-assign-parameters-ffa284ebde429704.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fix incorrect behavior in :class:`.CircuitData` in which, upon parameter assignment,
+    we attempted to modify the cached operation inside of a ``PackedInstruction``. Now
+    we instead discard said cache prompting the ``PackedInstruction`` to build a new Python
+    operation should it be needed.
\ No newline at end of file

From 2ec61bb4559715956497ed069aaf00089e849f50 Mon Sep 17 00:00:00 2001
From: Raynel Sanchez <87539502+raynelfss@users.noreply.github.com>
Date: Wed, 11 Dec 2024 14:36:12 -0500
Subject: [PATCH 3/4] Test: Add test case

---
 test/python/transpiler/test_basis_translator.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/test/python/transpiler/test_basis_translator.py b/test/python/transpiler/test_basis_translator.py
index 820c4f241a1..06762a78f1f 100644
--- a/test/python/transpiler/test_basis_translator.py
+++ b/test/python/transpiler/test_basis_translator.py
@@ -21,6 +21,7 @@
 from qiskit import QuantumRegister, ClassicalRegister, QuantumCircuit
 from qiskit import transpile
 from qiskit.circuit import Gate, Parameter, EquivalenceLibrary, Qubit, Clbit, Measure
+from qiskit.circuit.equivalence_library import StandardEquivalenceLibrary as std_eq_lib
 from qiskit.circuit.classical import expr, types
 from qiskit.circuit.library import (
     HGate,
@@ -481,6 +482,22 @@ def test_different_bits(self):
         out = BasisTranslator(std_eqlib, basis).run(circuit_to_dag(base))
         self.assertEqual(set(out.count_ops(recurse=True)), basis)
 
+    def test_correct_parameter_assignment(self):
+        """Test correct parameter assignment from an equivalence during translation"""
+        rx_key = next(key for key in std_eq_lib.keys() if key.name == "rx")
+
+        # The circuit doesn't need to be parametric.
+        qc = QuantumCircuit(1)
+        qc.rx(0.5, 0)
+
+        BasisTranslator(
+            equivalence_library=std_eq_lib,
+            target_basis=["cx", "id", "rz", "sx", "x"],
+        )(qc)
+
+        inst = std_eq_lib._get_equivalences(rx_key)[0].circuit.data[0]
+        self.assertEqual(inst.params, inst.operation.params)
+
 
 class TestUnrollerCompatability(QiskitTestCase):
     """Tests backward compatability with the Unroller pass.

From 0b5f59b7d8f4b60637799ada63e7e0847da2c9a4 Mon Sep 17 00:00:00 2001
From: Raynel Sanchez <87539502+raynelfss@users.noreply.github.com>
Date: Wed, 11 Dec 2024 17:15:53 -0500
Subject: [PATCH 4/4] Docs: Add relevant comment

---
 crates/circuit/src/circuit_data.rs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/crates/circuit/src/circuit_data.rs b/crates/circuit/src/circuit_data.rs
index 699ad5f3d1c..fa36d8b841f 100644
--- a/crates/circuit/src/circuit_data.rs
+++ b/crates/circuit/src/circuit_data.rs
@@ -1392,8 +1392,11 @@ impl CircuitData {
                             #[cfg(feature = "cache_pygates")]
                             {
                                 // Standard gates can all rebuild their definitions, so if the
-                                // cached py_op exists, update the `params` attribute and clear out
-                                // any existing cache.
+                                // cached py_op exists, discard it to prompt the instruction
+                                // to rebuild its cached python gate upon request later on. This is
+                                // done to avoid an unintentional duplicated reference to the same gate
+                                // instance in python. For more information, see
+                                // https://github.com/Qiskit/qiskit/issues/13504
                                 previous.py_op.take();
                             }
                         } else {