cherry-pick minor bugfixes from master (#4807)

**Context:**
These three bugs were identified as good to be released in a bugfix.

**Description of the Change:**
Cherry-pick the 3 commits to master onto this branch for the 0.33.1
bugfix release

**Benefits:**
Fixed bugs pushed out!

**Possible Drawbacks:**
Extra work in a critical time.

**Related GitHub Issues:**
#4768, #4781, #4787

---------

Co-authored-by: Christina Lee <[email protected]>
Co-authored-by: lillian542 <[email protected]>
Co-authored-by: Tom Bromley <[email protected]>
Co-authored-by: Mudit Pandey <[email protected]>

doc/releases/changelog-0.33.1.md

@@ -14,6 +14,21 @@
 
 <h3>Bug fixes 🐛</h3>
 
+* `qml.defer_measurements` now correctly transforms circuits when terminal measurements include wires
+  used in mid-circuit measurements.
+  [(#4787)](https://github.com/PennyLaneAI/pennylane/pull/4787)
+
+* Any `ScalarSymbolicOp`, like `Evolution`, now states that it has a matrix if the target
+  is a `Hamiltonian`.
+  [(#4768)](https://github.com/PennyLaneAI/pennylane/pull/4768)
+
+* In `default.qubit`, initial states are now initialized with the simulator's wire order, not the circuit's
+  wire order.
+  [(#4781)](https://github.com/PennyLaneAI/pennylane/pull/4781)
+
 <h3>Contributors ✍️</h3>
 
 This release contains contributions from (in alphabetical order):
+
+Christina Lee,
+Mudit Pandey

pennylane/devices/qubit/simulate.py

@@ -153,7 +153,7 @@ def get_final_state(circuit, debugger=None, interface=None):
     if len(circuit) > 0 and isinstance(circuit[0], qml.operation.StatePrepBase):
         prep = circuit[0]
 
-    state = create_initial_state(circuit.op_wires, prep, like=INTERFACE_TO_LIKE[interface])
+    state = create_initial_state(sorted(circuit.op_wires), prep, like=INTERFACE_TO_LIKE[interface])
 
     # initial state is batched only if the state preparation (if it exists) is batched
     is_state_batched = bool(prep and prep.batch_size is not None)

pennylane/ops/op_math/symbolicop.py

@@ -195,6 +195,10 @@ def _check_and_compute_batch_size(self, scalar):
             )
         return scalar_size
 
+    @property
+    def has_matrix(self):
+        return self.base.has_matrix or isinstance(self.base, qml.Hamiltonian)
+
     @property
     def hash(self):
         return hash(

pennylane/transforms/defer_measurements.py

@@ -66,7 +66,7 @@ def _collect_mid_measure_info(tape: QuantumTape):
     any_repeated_measurements = False
     is_postselecting = False
 
-    for op in tape.operations:
+    for op in tape:
         if isinstance(op, MidMeasureMP):
             if op.postselect is not None:
                 is_postselecting = True

tests/devices/default_qubit/test_default_qubit.py

@@ -317,6 +317,17 @@ def circuit(p):
         assert qml.math.get_interface(res) == "tensorflow"
         assert qml.math.allclose(res, -1)
 
+    def test_basis_state_wire_order(self):
+        """Test that the wire order is correct with a basis state if the tape wires have a non standard order."""
+
+        dev = DefaultQubit()
+
+        tape = qml.tape.QuantumScript([qml.BasisState([1], wires=1), qml.PauliZ(0)], [qml.state()])
+
+        expected = np.array([0, 1, 0, 0], dtype=np.complex128)
+        res = dev.execute(tape)
+        assert qml.math.allclose(res, expected)
+
 
 class TestSampleMeasurements:
     """A copy of the `qubit.simulate` tests, but using the device"""

tests/ops/op_math/test_symbolic_op.py

@@ -139,6 +139,13 @@ class DummyOp(Operator):
         op = SymbolicOp(base)
         assert op.has_matrix == has_mat
 
+    def test_has_matrix_hamiltonian(self):
+        """Test that it has a matrix if the base is a hamiltonian."""
+
+        H = qml.Hamiltonian([1.0], [qml.PauliX(0)])
+        op = TempScalar(H, 2)
+        assert op.has_matrix
+
     @pytest.mark.parametrize("is_herm", (True, False))
     def test_is_hermitian(self, is_herm):
         """Test that symbolic op is hermitian if the base is hermitian."""

tests/transforms/test_defer_measurements.py

@@ -1348,6 +1348,25 @@ def qnode2(x):
             for actual, expected in zip(qnode2.qtape.circuit, expected_circuit)
         )
 
+    def test_measurements_add_new_qubits(self):
+        """Test that qubit reuse related logic is applied if a wire with mid-circuit
+        measurements is included in terminal measurements."""
+        tape = qml.tape.QuantumScript(
+            ops=[qml.Hadamard(0), MidMeasureMP(0)], measurements=[qml.density_matrix(wires=[0])]
+        )
+        expected = np.eye(2) / 2
+
+        tapes, _ = qml.defer_measurements(tape)
+
+        dev = qml.device("default.qubit")
+        res = qml.execute(tapes, dev)
+
+        assert np.allclose(res, expected)
+
+        deferred_tape = tapes[0]
+        assert deferred_tape.operations == [qml.Hadamard(0), qml.CNOT([0, 1])]
+        assert deferred_tape.measurements == [qml.density_matrix(wires=[0])]
+
     def test_wire_is_reset(self):
         """Test that a wire is reset to the |0> state without any local phases
         after measurement if reset is requested."""
@@ -1484,7 +1503,7 @@ def test_custom_wire_labels_allowed_without_reset():
         qml.Hadamard("a")
         ma = qml.measure("a", reset=False)
         qml.cond(ma, qml.PauliX)("b")
-        qml.probs(wires="a")
+        qml.probs(wires="b")
 
     tape = qml.tape.QuantumScript.from_queue(q)
     tapes, _ = qml.defer_measurements(tape)
@@ -1493,7 +1512,7 @@ def test_custom_wire_labels_allowed_without_reset():
     assert len(tape) == 3
     assert qml.equal(tape[0], qml.Hadamard("a"))
     assert qml.equal(tape[1], qml.CNOT(["a", "b"]))
-    assert qml.equal(tape[2], qml.probs(wires="a"))
+    assert qml.equal(tape[2], qml.probs(wires="b"))
 
 
 def test_custom_wire_labels_fails_with_reset():