feat: Device-specific supported observables

src/braket/pennylane_plugin/braket_device.py

@@ -72,6 +72,7 @@
 
 from braket.pennylane_plugin.translation import (
     get_adjoint_gradient_result_type,
+    supported_observables,
     supported_operations,
     translate_operation,
     translate_result,
@@ -156,6 +157,7 @@ def __init__(
         self._parametrize_differentiable = parametrize_differentiable
         self._run_kwargs = run_kwargs
         self._supported_ops = supported_operations(self._device, verbatim=verbatim)
+        self._supported_obs = supported_observables(self._device, self.shots)
         self._check_supported_result_types()
         self._verbatim = verbatim
 
@@ -174,11 +176,7 @@ def operations(self) -> frozenset[str]:
 
     @property
     def observables(self) -> frozenset[str]:
-        base_observables = frozenset(super().observables)
-        # Amazon Braket only supports scalar multiplication and addition when shots==0
-        if not self.shots:
-            return base_observables.union({"Hamiltonian", "LinearCombination"})
-        return base_observables
+        return self._supported_obs
 
     @property
     def circuit(self) -> Circuit:

src/braket/pennylane_plugin/translation.py

@@ -28,6 +28,7 @@
     StateVector,
     Variance,
 )
+from braket.device_schema import DeviceActionType
 from braket.devices import Device
 from braket.pulse import ArbitraryWaveform, ConstantWaveform, PulseSequence
 from braket.tasks import GateModelQuantumTaskResult
@@ -96,6 +97,16 @@
 }
 
 
+_BRAKET_TO_PENNYLANE_OBSERVABLES = {
+    "x": frozenset({"PauliX"}),
+    "y": frozenset({"PauliY"}),
+    "z": frozenset({"PauliZ"}),
+    "h": frozenset({"Hadamard"}),
+    "hermitian": frozenset({"Hermitian", "Projector"}),
+    "i": frozenset({"Identity"}),
+}
+
+
 def supported_operations(device: Device, verbatim: bool = False) -> frozenset[str]:
     """Returns the operations supported by the plugin based upon the device.
 
@@ -111,7 +122,7 @@ def supported_operations(device: Device, verbatim: bool = False) -> frozenset[st
         properties = (
             device.properties.paradigm
             if verbatim
-            else device.properties.action["braket.ir.openqasm.program"]
+            else device.properties.action[DeviceActionType.OPENQASM]
         )
     except AttributeError:
         raise AttributeError("Device needs to have properties defined.")
@@ -514,6 +525,18 @@ def waveform(dt):
     return gates.PulseGate(pulse_sequence, qubit_count=len(op.wires))
 
 
+def supported_observables(device: Device, shots: int) -> frozenset[str]:
+    action = device.properties.action[DeviceActionType.OPENQASM]
+    braket_observables = set.union(
+        *[set(r.observables) for r in action.supportedResultTypes if r.observables]
+    )
+    supported = frozenset.union(
+        *[_BRAKET_TO_PENNYLANE_OBSERVABLES[braket_obs] for braket_obs in braket_observables],
+    )
+    supported |= {"Prod", "SProd"}
+    return supported if shots else supported | {"Sum", "Hamiltonian", "LinearCombination"}
+
+
 def get_adjoint_gradient_result_type(
     observable: Observable,
     targets: Union[list[int], list[list[int]]],

test/unit_tests/device_property_jsons.py

@@ -27,7 +27,7 @@
                 {"name": "StateVector", "observables": None, "minShots": 0, "maxShots": 0},
                 {
                     "name": "AdjointGradient",
-                    "observables": ["x", "y", "z", "h", "i"],
+                    "observables": ["x", "y", "z", "h", "i", "hermitian"],
                     "minShots": 0,
                     "maxShots": 0,
                 },
@@ -43,7 +43,12 @@
             "version": ["1"],
             "supportedOperations": ["rx", "ry", "h", "cy", "cnot", "unitary"],
             "supportedResultTypes": [
-                {"name": "StateVector", "observables": None, "minShots": 0, "maxShots": 0},
+                {
+                    "name": "StateVector",
+                    "observables": ["x", "y", "z"],
+                    "minShots": 0,
+                    "maxShots": 0,
+                },
             ],
         }
     )
@@ -56,7 +61,12 @@
             "version": ["1"],
             "supportedOperations": ["rx", "ry", "h", "cy", "cnot", "unitary"],
             "supportedResultTypes": [
-                {"name": "StateVector", "observables": None, "minShots": 0, "maxShots": 0},
+                {
+                    "name": "StateVector",
+                    "observables": ["x", "y", "z"],
+                    "minShots": 0,
+                    "maxShots": 0,
+                },
             ],
             "supportedPragmas": [
                 "braket_noise_bit_flip",

test/unit_tests/test_braket_device.py

@@ -1935,7 +1935,7 @@ def properties(self) -> GateModelSimulatorDeviceCapabilities:
                     "supportedResultTypes": [
                         {
                             "name": "resultType1",
-                            "observables": ["observable1"],
+                            "observables": ["z"],
                             "minShots": 2,
                             "maxShots": 4,
                         }

test/unit_tests/test_shadow_expval.py

@@ -395,7 +395,7 @@ def properties(self) -> GateModelSimulatorDeviceCapabilities:
                     "supportedResultTypes": [
                         {
                             "name": "resultType1",
-                            "observables": ["observable1"],
+                            "observables": ["z"],
                             "minShots": 2,
                             "maxShots": 4,
                         }