More sophisiticated measurement validation for default-qubit

pennylane/devices/default_qubit.py

@@ -60,30 +60,6 @@
 PostprocessingFn = Callable[[ResultBatch], Result_or_ResultBatch]
 
 
-observables = {
- "PauliX",
- "PauliY",
- "PauliZ",
- "Hadamard",
- "Hermitian",
- "Identity",
- "Projector",
- "SparseHamiltonian",
- "Hamiltonian",
- "LinearCombination",
- "Sum",
- "SProd",
- "Prod",
- "Exp",
- "Evolution",
-}
-
-
-def observable_stopping_condition(obs: qml.operation.Operator) -> bool:
- """Specifies whether or not an observable is accepted by DefaultQubit."""
- return obs.name in observables
-
-
 def stopping_condition(op: qml.operation.Operator) -> bool:
  """Specify whether or not an Operator object is supported by the device."""
  if op.name == "QFT" and len(op.wires) >= 6:
@@ -103,16 +79,62 @@ def stopping_condition_shots(op: qml.operation.Operator) -> bool:
  return isinstance(op, (Conditional, MidMeasureMP)) or stopping_condition(op)
 
 
+def observable_accepts_sampling(obs: qml.operation.Operator) -> bool:
+ """Verifies whether an observable supports sample measurement"""
+
+ if isinstance(obs, qml.ops.CompositeOp):
+ return all(observable_accepts_sampling(o) for o in obs.operands)
+
+ if isinstance(obs, qml.operation.Tensor):
+ return all(observable_accepts_sampling(o) for o in obs.obs)
+
+ return obs.has_diagonalizing_gates()
+
+
+def observable_accepts_analytic(obs: qml.operation.Operator, is_expval=False) -> bool:
+ """Verifies whether an observable supports analytic measurement"""
+
+ if isinstance(obs, qml.ops.CompositeOp):
+ return all(observable_accepts_analytic(o, is_expval) for o in obs.operands)
+
+ if obs.has_diagonalizing_gates():
+ return True
+
+ if is_expval:
+ return isinstance(obs, (qml.ops.SparseHamiltonian, qml.ops.Hermitian))
+
+ return True
+
+
 def accepted_sample_measurement(m: qml.measurements.MeasurementProcess) -> bool:
- """Specifies whether or not a measurement is accepted when sampling."""
- return isinstance(
+ """Specifies whether a measurement is accepted when sampling."""
+
+ if not isinstance(
  m,
  (
  qml.measurements.SampleMeasurement,
  qml.measurements.ClassicalShadowMP,
  qml.measurements.ShadowExpvalMP,
  ),
- )
+ ):
+ return False
+
+ if m.obs is not None:
+ return observable_accepts_sampling(m.obs)
+
+ return True
+
+
+def accepted_analytic_measurement(m: qml.measurements.MeasurementProcess) -> bool:
+ """Specifies whether a measurement is accepted when analytic."""
+
+ if not isinstance(m, qml.measurements.StateMeasurement):
+ return False
+
+ if m.obs is not None:
+ return observable_accepts_analytic(m.obs, isinstance(m, qml.measurements.ExpectationMP))
+
+ return True
 
 
 def null_postprocessing(results):
@@ -514,10 +536,10 @@ def preprocess(
  name=self.name,
  )
  transform_program.add_transform(
- validate_measurements, sample_measurements=accepted_sample_measurement, name=self.name
- )
- transform_program.add_transform(
- validate_observables, stopping_condition=observable_stopping_condition, name=self.name
+ validate_measurements,
+  analytic_measurements=accepted_analytic_measurement,
+  sample_measurements=accepted_sample_measurement,
+ name=self.name,
  )
  if config.mcm_config.mcm_method == "tree-traversal":
  transform_program.add_transform(qml.transforms.broadcast_expand)