Barebone generic backend options (#12747)

* Update generic_backend_v2.py

* reno

* Update barebone-backend-option-675c86df4382a443.yaml

* ...

* suggestions from code review

* Update barebone-backend-option-675c86df4382a443.yaml

* tests, typo

qiskit/providers/fake_provider/generic_backend_v2.py

@@ -112,6 +112,8 @@ class GenericBackendV2(BackendV2):
         calibrate_instructions: bool | InstructionScheduleMap | None = None,
         dtm: float | None = None,
         seed: int | None = None,
+        pulse_channels: bool = True,
+        noise_info: bool = True,
     ):
         """
         Args:
@@ -159,6 +161,10 @@ class GenericBackendV2(BackendV2):
                 None by default.
 
             seed: Optional seed for generation of default values.
+
+            pulse_channels: If true, sets default pulse channel information on the backend.
+
+            noise_info: If true, associates gates and qubits with default noise information.
         """
 
         super().__init__(
@@ -175,6 +181,10 @@ class GenericBackendV2(BackendV2):
         self._control_flow = control_flow
         self._calibrate_instructions = calibrate_instructions
         self._supported_gates = get_standard_gate_name_mapping()
+        self._noise_info = noise_info
+
+        if calibrate_instructions and not noise_info:
+            raise QiskitError("Must set parameter noise_info when calibrating instructions.")
 
         if coupling_map is None:
             self._coupling_map = CouplingMap().from_full(num_qubits)
@@ -198,7 +208,10 @@ class GenericBackendV2(BackendV2):
                 self._basis_gates.append(name)
 
         self._build_generic_target()
-        self._build_default_channels()
+        if pulse_channels:
+            self._build_default_channels()
+        else:
+            self.channels_map = {}
 
     @property
     def target(self):
@@ -340,22 +353,31 @@ class GenericBackendV2(BackendV2):
         """
         # the qubit properties are sampled from default ranges
         properties = _QUBIT_PROPERTIES
-        self._target = Target(
-            description=f"Generic Target with {self._num_qubits} qubits",
-            num_qubits=self._num_qubits,
-            dt=properties["dt"],
-            qubit_properties=[
-                QubitProperties(
-                    t1=self._rng.uniform(properties["t1"][0], properties["t1"][1]),
-                    t2=self._rng.uniform(properties["t2"][0], properties["t2"][1]),
-                    frequency=self._rng.uniform(
-                        properties["frequency"][0], properties["frequency"][1]
-                    ),
-                )
-                for _ in range(self._num_qubits)
-            ],
-            concurrent_measurements=[list(range(self._num_qubits))],
-        )
+        if not self._noise_info:
+            self._target = Target(
+                description=f"Generic Target with {self._num_qubits} qubits",
+                num_qubits=self._num_qubits,
+                dt=properties["dt"],
+                qubit_properties=None,
+                concurrent_measurements=[list(range(self._num_qubits))],
+            )
+        else:
+            self._target = Target(
+                description=f"Generic Target with {self._num_qubits} qubits",
+                num_qubits=self._num_qubits,
+                dt=properties["dt"],
+                qubit_properties=[
+                    QubitProperties(
+                        t1=self._rng.uniform(properties["t1"][0], properties["t1"][1]),
+                        t2=self._rng.uniform(properties["t2"][0], properties["t2"][1]),
+                        frequency=self._rng.uniform(
+                            properties["frequency"][0], properties["frequency"][1]
+                        ),
+                    )
+                    for _ in range(self._num_qubits)
+                ],
+                concurrent_measurements=[list(range(self._num_qubits))],
+            )
 
         # Generate instruction schedule map with calibrations to add to target.
         calibration_inst_map = None
@@ -380,8 +402,11 @@ class GenericBackendV2(BackendV2):
                     f"Provided basis gate {name} needs more qubits than {self.num_qubits}, "
                     f"which is the size of the backend."
                 )
-            noise_params = self._get_noise_defaults(name, gate.num_qubits)
-            self._add_noisy_instruction_to_target(gate, noise_params, calibration_inst_map)
+            if self._noise_info:
+                noise_params = self._get_noise_defaults(name, gate.num_qubits)
+                self._add_noisy_instruction_to_target(gate, noise_params, calibration_inst_map)
+            else:
+                self._target.add_instruction(gate, properties=None, name=name)
 
         if self._control_flow:
             self._target.add_instruction(IfElseOp, name="if_else")

releasenotes/notes/barebone-backend-option-675c86df4382a443.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Added two parameters to :class:`.GenericBackendV2` to exclude error (`noise_info`) and
+    pulse channel information (`pulse_channels`) from the construction of the backend. These parameters
+    are true by default, replicating the initial default behavior of the constructor. A memory-sensitive
+    user may set these options to `False` to reduce the memory overhead by 40x when transpiling on large-
+    scale :class:`.GenericBackendV2`.

test/python/providers/fake_provider/test_generic_backend_v2.py

@@ -45,6 +45,26 @@ class TestGenericBackendV2(QiskitTestCase):
         with self.assertRaises(QiskitError):
             GenericBackendV2(num_qubits=2, basis_gates=["ccx", "id"])
 
+    def test_calibration_no_noise_info(self):
+        """Test failing with a backend with calibration and no noise info"""
+        with self.assertRaises(QiskitError):
+            GenericBackendV2(
+                num_qubits=2,
+                basis_gates=["ccx", "id"],
+                calibrate_instructions=True,
+                noise_info=False,
+            )
+
+    def test_no_noise(self):
+        """Test no noise info when parameter is false"""
+        backend = GenericBackendV2(num_qubits=2, noise_info=False)
+        self.assertEqual(backend.target.qubit_properties, None)
+
+    def test_no_pulse_channels(self):
+        """Test no/empty pulse channels when parameter is false"""
+        backend = GenericBackendV2(num_qubits=2, pulse_channels=False)
+        self.assertTrue(len(backend.channels_map) == 0)
+
     def test_operation_names(self):
         """Test that target basis gates include "delay", "measure" and "reset" even
         if not provided by user."""