Fix disassemble of isometry and added test_disassemble_isometry (#4402)

* Treat call to isometry in disassemble as special case

* Added test_disassemble_isometry

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

qiskit/assembler/disassemble.py

@@ -77,6 +77,8 @@ def _experiments_to_circuits(qobj):
                             params=params)
                     elif i.name == 'initialize':
                         _inst = instr_method(params, qubits)
+                    elif i.name == 'isometry':
+                        _inst = instr_method(*params, qubits, clbits)
                     else:
                         _inst = instr_method(*params, *qubits, *clbits)
                 elif name == 'bfunc':

test/python/compiler/test_disassembler.py

@@ -17,13 +17,15 @@
 import unittest
 
 import numpy as np
+from numpy.testing import assert_allclose
 
 from qiskit.circuit import QuantumRegister, ClassicalRegister, QuantumCircuit
 from qiskit.circuit import Instruction
 from qiskit.compiler.assemble import assemble
 from qiskit.assembler.disassemble import disassemble
 from qiskit.assembler.run_config import RunConfig
 from qiskit.test import QiskitTestCase
+import qiskit.quantum_info as qi
 
 
 class TestAssembler(QiskitTestCase):
@@ -116,6 +118,26 @@ def test_assemble_initialize(self):
         self.assertEqual(circuits[0], circ)
         self.assertEqual({}, header)
 
+    def test_disassemble_isometry(self):
+        """Test disassembling a circuit with an isometry.
+        """
+        q = QuantumRegister(2, name='q')
+        circ = QuantumCircuit(q, name='circ')
+        circ.iso(qi.random_unitary(4).data, circ.qubits, [])
+        qobj = assemble(circ)
+        circuits, run_config_out, header = disassemble(qobj)
+        run_config_out = RunConfig(**run_config_out)
+        self.assertEqual(run_config_out.n_qubits, 2)
+        self.assertEqual(run_config_out.memory_slots, 0)
+        self.assertEqual(len(circuits), 1)
+        # params array
+        assert_allclose(circuits[0]._data[0][0].params[0], circ._data[0][0].params[0])
+        # all other data
+        self.assertEqual(circuits[0]._data[0][0].params[1:], circ._data[0][0].params[1:])
+        self.assertEqual(circuits[0]._data[0][1:], circ._data[0][1:])
+        self.assertEqual(circuits[0]._data[1:], circ._data[1:])
+        self.assertEqual({}, header)
+
     def test_opaque_instruction(self):
         """Test the disassembler handles opaque instructions correctly."""
         opaque_inst = Instruction(name='my_inst', num_qubits=4,