Fix device noise model from BackendV2 not to have excessive quantum errors on measures/resets

qiskit_aer/noise/device/models.py

@@ -21,6 +21,7 @@
 from numpy import inf, exp, allclose
 
 import qiskit.quantum_info as qi
+from qiskit.circuit import Gate, Measure
 from .parameters import _NANOSECOND_UNITS
 from .parameters import gate_param_values
 from .parameters import readout_error_values
@@ -78,7 +79,7 @@ def basic_device_readout_errors(properties=None, target=None):
     return errors
 
 
-def basic_device_gate_errors(properties,
+def basic_device_gate_errors(properties=None,
                              gate_error=True,
                              thermal_relaxation=True,
                              gate_lengths=None,
@@ -88,16 +89,21 @@ def basic_device_gate_errors(properties,
                              warnings=None,
                              target=None):
     """
-    Return QuantumErrors derived from a devices BackendProperties.
+    Return QuantumErrors derived from either of a devices BackendProperties or Target.
 
     If non-default values are used gate_lengths should be a list
     of tuples ``(name, qubits, value)`` where ``name`` is the gate
     name string, ``qubits`` is either a list of qubits or ``None``
     to apply gate time to this gate one any set of qubits,
     and ``value`` is the gate time in nanoseconds.
 
+    The resulting errors may contains two types of errors: gate errors and relaxation errors.
+    The gate errors are generated only for ``Gate`` objects while the relaxation errors are
+    generated for all ``Instruction`` objects. Exceptionally, no ``QuantumError`` s are
+    generated for ``Measure`` since ``ReadoutError`` s are generated separately instead.
+
     Args:
-        properties (BackendProperties): device backend properties
+        properties (BackendProperties): device backend properties.
         gate_error (bool): Include depolarizing gate errors (Default: True).
         thermal_relaxation (Bool): Include thermal relaxation errors
                                    (Default: True).
@@ -126,6 +132,9 @@ def basic_device_gate_errors(properties,
     Raises:
         NoiseError: If invalid arguments are supplied.
     """
+    if properties is None and target is None:
+        raise NoiseError("Either properties or target must be supplied.")
+
     if standard_gates is not None:
         warn(
             '"standard_gates" option has been deprecated as of qiskit-aer 0.10.0'
@@ -156,9 +165,6 @@ def basic_device_gate_errors(properties,
             temperature=temperature
         )
 
-    # Initilize empty errors
-    depol_error = None
-    relax_error = None
     # Generate custom gate time dict
     custom_times = {}
     relax_params = []
@@ -182,6 +188,9 @@ def basic_device_gate_errors(properties,
     # Construct quantum errors
     errors = []
     for name, qubits, gate_length, error_param in device_gate_params:
+        # Initilize empty errors
+        depol_error = None
+        relax_error = None
         # Check for custom gate time
         relax_time = gate_length
         # Override with custom value
@@ -232,9 +241,16 @@ def _basic_device_target_gate_errors(target,
                                      gate_error=True,
                                      thermal_relaxation=True,
                                      temperature=0):
-    """Return QuantumErrors derived from a devices Target."""
+    """Return QuantumErrors derived from a devices Target.
+    Note that, in the resulting error list, non-Gate instructions (e.g. Reset) will have
+    no gate errors while they may have thermal relaxation errors. Exceptionally,
+    Measure instruction will have no errors, neither gate errors nor relaxation errors.
+    """
     errors = []
     for op_name, inst_prop_dic in target.items():
+        operation = target.operation_from_name(op_name)
+        if isinstance(operation, Measure):
+            continue
         if inst_prop_dic is None:  # ideal simulator
             continue
         for qubits, inst_prop in inst_prop_dic.items():
@@ -255,7 +271,7 @@ def _basic_device_target_gate_errors(target,
                     temperature=temperature,
                 )
             # Get depolarizing error
-            if gate_error and inst_prop.error:
+            if gate_error and inst_prop.error and isinstance(operation, Gate):
                 depol_error = _device_depolarizing_error(
                     qubits=qubits,
                     error_param=inst_prop.error,
@@ -315,8 +331,14 @@ def _device_depolarizing_error(qubits,
         max_param = 4**num_qubits / (4**num_qubits - 1)
         if depol_param > max_param:
             depol_param = min(depol_param, max_param)
-        return depolarizing_error(
-            depol_param, num_qubits, standard_gates=standard_gates)
+        with catch_warnings():
+            filterwarnings(
+                "ignore",
+                category=DeprecationWarning,
+                module="qiskit_aer.noise.device.models"
+            )
+            return depolarizing_error(
+                depol_param, num_qubits, standard_gates=standard_gates)
     return None
 
 

releasenotes/notes/fix-device-noise-models-2eca2f9c9dc25771.yaml

@@ -0,0 +1,11 @@
+---
+fixes:
+  - |
+    Fixes a bug where :meth:`NoiseModel.from_backend` with a ``BackendV2`` object may generate
+    a noise model with excessive ``QuantumError`` s on non-Gate instructions while,
+    for example, only ``ReadoutError`` s should be sufficient for measures.
+    This commit updates :meth:`NoiseModel.from_backend` with a ``BackendV2`` object so that
+    it returns the same noise model as that called with the corresponding ``BackendV1`` object.
+    That is, the resulting noise model does not contain any ``QuantumError`` s on measures and
+    it may contain only thermal relaxation errors on other non-gate instructions such as resets.
+    Note that it still contains ``ReadoutError`` s on measures.

test/terra/noise/test_device_models.py

@@ -0,0 +1,46 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2022.
+#
+# 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.
+
+"""
+Tests for utility functions to create device noise model.
+"""
+
+from test.terra.common import QiskitAerTestCase
+
+from qiskit.providers.fake_provider import FakeNairobi, FakeNairobiV2
+from qiskit_aer.noise.device.models import basic_device_gate_errors
+
+
+class TestDeviceNoiseModel(QiskitAerTestCase):
+    """Testing device noise model"""
+
+    def test_basic_device_gate_errors_from_target(self):
+        """Test if the resulting gate errors never include errors on non-gate instructions"""
+        target = FakeNairobiV2().target
+        gate_errors = basic_device_gate_errors(target=target)
+        errors_on_measure = [name for name, _, _ in gate_errors if name == "measure"]
+        errors_on_reset = [name for name, _, _ in gate_errors if name == "reset"]
+        self.assertEqual(len(errors_on_measure), 0)
+        self.assertEqual(len(errors_on_reset), 7)
+        self.assertEqual(len(gate_errors), 40)
+
+    def test_basic_device_gate_errors_from_target_and_properties(self):
+        """Test if the device same gate errors are produced both from target and properties"""
+        errors_from_properties = basic_device_gate_errors(properties=FakeNairobi().properties())
+        errors_from_target = basic_device_gate_errors(target=FakeNairobiV2().target)
+        self.assertEqual(len(errors_from_properties), len(errors_from_target))
+        for err_properties, err_target in zip(errors_from_properties, errors_from_target):
+            name1, qargs1, err1 = err_properties
+            name2, qargs2, err2 = err_target
+            self.assertEqual(name1, name2)
+            self.assertEqual(tuple(qargs1), qargs2)
+            self.assertEqual(err1, err2)