Fix to carry over calibrations with __iadd__ and __add__ (#5910)

* * Added fix to carry over calibrations with __iadd__ and __add__.
* Added corresponding test.

* * Added reno.

* * Lint fix.

* * Switched to add_calibration.

* * Removed the redundent comments.

qiskit/circuit/quantumcircuit.py

@@ -566,6 +566,11 @@ def combine(self, rhs):
         for instruction_context in itertools.chain(self.data, rhs.data):
             circuit._append(*instruction_context)
         circuit.global_phase = self.global_phase + rhs.global_phase
+
+        for gate, cals in rhs.calibrations.items():
+            for key, sched in cals.items():
+                circuit.add_calibration(gate, qubits=key[0], schedule=sched, params=key[1])
+
         return circuit
 
     def extend(self, rhs):
@@ -610,6 +615,11 @@ def extend(self, rhs):
         for instruction_context in data:
             self._append(*instruction_context)
         self.global_phase += rhs.global_phase
+
+        for gate, cals in rhs.calibrations.items():
+            for key, sched in cals.items():
+                self.add_calibration(gate, qubits=key[0], schedule=sched, params=key[1])
+
         return self
 
     def compose(self, other, qubits=None, clbits=None, front=False, inplace=False):

releasenotes/notes/calibrations-add-iadd-265b92f42ffce92a.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Quantum circuit Calibrations are now carried over when the operators += and +
+    are used.

test/python/circuit/test_calibrations.py

@@ -0,0 +1,51 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2021.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Test calibrations in quantum circuits."""
+
+import unittest
+
+from qiskit.pulse import Schedule
+from qiskit.circuit import QuantumCircuit
+from qiskit.circuit.library import RZXGate
+from qiskit.test import QiskitTestCase
+
+
+class TestCalibrations(QiskitTestCase):
+    """Test composition of two circuits."""
+
+    def test_iadd(self):
+        """Test that __iadd__ keeps the calibrations."""
+        qc_cal = QuantumCircuit(2)
+        qc_cal.rzx(0.5, 0, 1)
+        qc_cal.add_calibration(RZXGate, (0, 1), params=[0.5], schedule=Schedule())
+
+        qc = QuantumCircuit(2)
+        qc += qc_cal
+
+        self.assertEqual(qc.calibrations[RZXGate], {((0, 1), (0.5,)): Schedule(name="test")})
+        self.assertEqual(qc_cal.calibrations, qc.calibrations)
+
+    def test_add(self):
+        """Test that __add__ keeps the calibrations."""
+        qc_cal = QuantumCircuit(2)
+        qc_cal.rzx(0.5, 0, 1)
+        qc_cal.add_calibration(RZXGate, (0, 1), params=[0.5], schedule=Schedule())
+
+        qc = QuantumCircuit(2) + qc_cal
+
+        self.assertEqual(qc.calibrations[RZXGate], {((0, 1), (0.5,)): Schedule(name="test")})
+        self.assertEqual(qc_cal.calibrations, qc.calibrations)
+
+
+if __name__ == '__main__':
+    unittest.main()