From 5a250c7ae6dc6cb1031462adbf55bfca9a13d440 Mon Sep 17 00:00:00 2001
From: SoranaAurelia <52232581+SoranaAurelia@users.noreply.github.com>
Date: Sat, 18 Nov 2023 01:55:17 +0200
Subject: [PATCH] Allow correct retrieval of circuit with initialize
 instruction from qpy file (#11206)

* treated cases for StatePreparation initialization when reading from qpy file

* added test for state preparation from qpy

* added docstring to test function

* added fix release note

* Fixup release note

---------

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
(cherry picked from commit 9111d0f9e198a87433da2d5dd8fa9427b9140194)
---
 qiskit/qpy/binary_io/circuits.py                   | 14 +++++++++++---
 ...tatepreparation-retrieval-1feea5eb74db7f1e.yaml |  5 +++++
 test/python/circuit/test_circuit_load_from_qpy.py  | 12 ++++++++++++
 3 files changed, 28 insertions(+), 3 deletions(-)
 create mode 100644 releasenotes/notes/fix-qpy-statepreparation-retrieval-1feea5eb74db7f1e.yaml

diff --git a/qiskit/qpy/binary_io/circuits.py b/qiskit/qpy/binary_io/circuits.py
index 81785bf78151..6d910746a89a 100644
--- a/qiskit/qpy/binary_io/circuits.py
+++ b/qiskit/qpy/binary_io/circuits.py
@@ -319,9 +319,17 @@ def _read_instruction(
         if condition:
             gate = gate.c_if(*condition)
     else:
-        if gate_name in {
-            "Initialize",
-            "StatePreparation",
+        if gate_name in {"Initialize", "StatePreparation"}:
+            if isinstance(params[0], str):
+                # the params are the labels of the initial state
+                gate = gate_class("".join(label for label in params))
+            elif instruction.num_parameters == 1:
+                # the params is the integer indicating which qubits to initialize
+                gate = gate_class(int(params[0].real), instruction.num_qargs)
+            else:
+                # the params represent a list of complex amplitudes
+                gate = gate_class(params)
+        elif gate_name in {
             "UCRXGate",
             "UCRYGate",
             "UCRZGate",
diff --git a/releasenotes/notes/fix-qpy-statepreparation-retrieval-1feea5eb74db7f1e.yaml b/releasenotes/notes/fix-qpy-statepreparation-retrieval-1feea5eb74db7f1e.yaml
new file mode 100644
index 000000000000..67cdafcb463a
--- /dev/null
+++ b/releasenotes/notes/fix-qpy-statepreparation-retrieval-1feea5eb74db7f1e.yaml
@@ -0,0 +1,5 @@
+fixes:
+  - |
+    Fixed QPY deserialization of the :class:`.StatePreparation` and :class:`.Initialize` circuit
+    instructions with string and integer parameters (as opposed to an explicit statevector, which
+    was already working).  Fixed `#11158 <https://github.com/Qiskit/qiskit/issues/11158>`__.
diff --git a/test/python/circuit/test_circuit_load_from_qpy.py b/test/python/circuit/test_circuit_load_from_qpy.py
index f8ba8c260df9..4f8523358dbd 100644
--- a/test/python/circuit/test_circuit_load_from_qpy.py
+++ b/test/python/circuit/test_circuit_load_from_qpy.py
@@ -1685,6 +1685,18 @@ def test_qpy_deprecation(self):
             # pylint: disable=no-name-in-module, unused-import, redefined-outer-name, reimported
             from qiskit.circuit.qpy_serialization import dump, load
 
+    @ddt.data(0, "01", [1, 0, 0, 0])
+    def test_valid_circuit_with_initialize_instruction(self, param):
+        """Tests that circuit that has initialize instruction can be saved and correctly retrieved"""
+        qc = QuantumCircuit(2)
+        qc.initialize(param, qc.qubits)
+        with io.BytesIO() as fptr:
+            dump(qc, fptr)
+            fptr.seek(0)
+            new_circuit = load(fptr)[0]
+        self.assertEqual(qc, new_circuit)
+        self.assertDeprecatedBitProperties(qc, new_circuit)
+
 
 class TestSymengineLoadFromQPY(QiskitTestCase):
     """Test use of symengine in qpy set of methods."""