Convert delays to instructions when assembling (#5481)

* Convert delays to instructions when assembling

* Add reno

* Fixup copy paste error

* Remove failing test

* Add test for regular delay inst

* Respond to feedback

* Update disassembler tests

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

qiskit/assembler/assemble_schedules.py

@@ -198,10 +198,6 @@ def _assemble_instructions(
             acquire_instruction_map[(time, instruction.duration)].append(instruction)
             continue
 
-        if isinstance(instruction, (instructions.Delay, instructions.Directive)):
-            # delay instructions are ignored as timing is explicit within qobj
-            continue
-
         qobj_instructions.append(instruction_converter(time, instruction))
 
     if acquire_instruction_map:

qiskit/qobj/converters/pulse_instruction.py

@@ -341,6 +341,24 @@ def convert_shift_phase(self, shift, instruction):
         }
         return self._qobj_model(**command_dict)
 
+    @bind_instruction(instructions.Delay)
+    def convert_delay(self, shift, instruction):
+        """Return converted `Delay`.
+
+        Args:
+            shift(int): Offset time.
+            instruction (Delay): Delay instruction.
+        Returns:
+            dict: Dictionary of required parameters.
+        """
+        command_dict = {
+            'name': 'delay',
+            't0': shift + instruction.start_time,
+            'ch': instruction.channel.name,
+            'duration': instruction.duration
+        }
+        return self._qobj_model(**command_dict)
+
     @bind_instruction(instructions.Play)
     def convert_play(self, shift, instruction):
         """Return the converted `Play`.

releasenotes/notes/bugfix-assemble-delay-32a96b59bb84badd.yaml

@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    Pulse :py:class:`~qiskit.pulse.instructions.Delay` is now explicitly
+    assembled as qobj instructions.
+
+    Previously, we could ignore delays rather than assembling them. Now, with
+    pulse gates, there are times that we want to schedule ONLY a delay, and not
+    including the delay itself would remove the delay.

test/python/compiler/test_assembler.py

@@ -548,6 +548,17 @@ def test_pulse_gates_common_cals(self):
         self.assertEqual(len(qobj.experiments[0].config.calibrations.gates), 1)
         self.assertFalse(hasattr(qobj.experiments[1].config, 'calibrations'))
 
+    def test_pulse_gates_delay_only(self):
+        """Test that a single delay gate is translated to an instruction."""
+        circ = QuantumCircuit(2)
+        circ.append(Gate('test', 1, []), [0])
+        test_sched = pulse.Delay(64, DriveChannel(0)) + pulse.Delay(160, DriveChannel(0))
+        circ.add_calibration('test', [0], test_sched)
+        qobj = assemble(circ, FakeOpenPulse2Q())
+        self.assertEqual(len(qobj.config.calibrations.gates[0].instructions), 2)
+        self.assertEqual(qobj.config.calibrations.gates[0].instructions[1].to_dict(),
+                         {"name": "delay", "t0": 64, "ch": "d0", "duration": 160})
+
 
 class TestPulseAssembler(QiskitTestCase):
     """Tests for assembling schedules to qobj."""
@@ -836,16 +847,13 @@ def test_pulse_name_conflicts_in_other_schedule(self):
 
     def test_assemble_with_delay(self):
         """Test that delay instruction is ignored in assembly."""
-        orig_schedule = self.schedule
-        delay_schedule = orig_schedule + pulse.Delay(10, self.backend_config.drive(0))
-
-        orig_qobj = assemble(orig_schedule, self.backend)
-        validate_qobj_against_schema(orig_qobj)
+        delay_schedule = pulse.Delay(10, self.backend_config.drive(0))
+        delay_schedule += self.schedule
         delay_qobj = assemble(delay_schedule, self.backend)
-        validate_qobj_against_schema(delay_qobj)
 
-        self.assertEqual(orig_qobj.experiments[0].to_dict(),
-                         delay_qobj.experiments[0].to_dict())
+        validate_qobj_against_schema(delay_qobj)
+        self.assertEqual(delay_qobj.experiments[0].instructions[0].name, "delay")
+        self.assertEqual(delay_qobj.experiments[0].instructions[0].duration, 10)
 
     def test_assemble_schedule_enum(self):
         """Test assembling a schedule with enum input values to assemble."""

test/python/compiler/test_disassembler.py

@@ -251,7 +251,7 @@ def test_disassemble_single_schedule(self):
         self.assertEqual(run_config_out.qubit_lo_freq, self.backend.defaults().qubit_freq_est)
         self.assertEqual(run_config_out.rep_time, 99)
         self.assertEqual(len(scheds), 1)
-        self.assertEqual(scheds[0], sched.exclude(instruction_types=[pulse.Delay]))
+        self.assertEqual(scheds[0], sched)
 
     def test_disassemble_multiple_schedules(self):
         """Test disassembling multiple schedules, all should have the same config.
@@ -290,8 +290,8 @@ def test_disassemble_multiple_schedules(self):
         self.assertEqual(run_config_out.shots, 2000)
         self.assertEqual(run_config_out.memory, False)
         self.assertEqual(len(scheds), 2)
-        self.assertEqual(scheds[0], sched0.exclude(instruction_types=[pulse.Delay]))
-        self.assertEqual(scheds[1], sched1.exclude(instruction_types=[pulse.Delay]))
+        self.assertEqual(scheds[0], sched0)
+        self.assertEqual(scheds[1], sched1)
 
     def test_disassemble_parametric_pulses(self):
         """Test disassembling multiple schedules all should have the same config.