Accept all_qubits in GridDevice._from_device_information() to allow isolated qubits (#6103)

Author: verult

cirq-google/cirq_google/devices/grid_device.py

@@ -510,7 +510,8 @@ def _from_device_information(
         *,
         qubit_pairs: Collection[Tuple[cirq.GridQubit, cirq.GridQubit]],
         gateset: cirq.Gateset,
-        gate_durations: Optional[Mapping['cirq.GateFamily', 'cirq.Duration']] = None,
+        gate_durations: Optional[Mapping[cirq.GateFamily, cirq.Duration]] = None,
+        all_qubits: Optional[Collection[cirq.GridQubit]] = None,
     ) -> 'GridDevice':
         """Constructs a GridDevice using the device information provided.
 
@@ -555,9 +556,14 @@ def _from_device_information(
             ValueError: If `gate_durations` contains keys which are not in `gateset`.
             ValueError: If multiple gate families in gate_durations can
                 represent a particular gate, but they have different durations.
+            ValueError: If all_qubits is provided and is not a superset
+                of all the qubits found in qubit_pairs.
         """
         metadata = cirq.GridDeviceMetadata(
-            qubit_pairs=qubit_pairs, gateset=gateset, gate_durations=gate_durations
+            qubit_pairs=qubit_pairs,
+            gateset=gateset,
+            gate_durations=gate_durations,
+            all_qubits=all_qubits,
         )
         incomplete_device = GridDevice(metadata)
         # incomplete_device may have incomplete gateset and gate durations information, as described

cirq-google/cirq_google/devices/grid_device_test.py

@@ -204,6 +204,24 @@ def _create_device_spec_with_all_couplings():
     return spec
 
 
+def _create_device_spec_with_isolated_qubits():
+    # Qubit layout:
+    #   x -- x
+    #   x -- x
+    #   x -- x
+    #   x -- x
+    #   x -- x
+    #   x    x
+    device_info, spec = _create_device_spec_with_horizontal_couplings()
+
+    isolated_qubits = [cirq.GridQubit(GRID_HEIGHT, j) for j in range(2)]
+    spec.valid_qubits.extend([v2.qubit_to_proto_id(q) for q in isolated_qubits])
+
+    device_info.grid_qubits.extend(isolated_qubits)
+
+    return device_info, spec
+
+
 def _create_device_spec_duplicate_qubit() -> v2.device_pb2.DeviceSpecification:
     """Creates a DeviceSpecification with a qubit name that does not conform to '<int>_<int>'."""
     q_proto_id = v2.qubit_to_proto_id(cirq.GridQubit(0, 0))
@@ -440,7 +458,7 @@ def test_grid_device_repr_pretty(cycle, func):
 
 
 def test_device_from_device_information_equals_device_from_proto():
-    device_info, spec = _create_device_spec_with_horizontal_couplings()
+    device_info, spec = _create_device_spec_with_isolated_qubits()
 
     # The set of gates in gateset and gate durations are consistent with what's generated in
     # _create_device_spec_with_horizontal_couplings()
@@ -482,7 +500,10 @@ def test_device_from_device_information_equals_device_from_proto():
     }
 
     device_from_information = cirq_google.GridDevice._from_device_information(
-        qubit_pairs=device_info.qubit_pairs, gateset=gateset, gate_durations=gate_durations
+        qubit_pairs=device_info.qubit_pairs,
+        gateset=gateset,
+        gate_durations=gate_durations,
+        all_qubits=device_info.grid_qubits,
     )
 
     assert device_from_information == cirq_google.GridDevice.from_proto(spec)