Break intermediate measurements on 3+ qubits into single qubit measurements in RouteCQC#6293

cirq-core/cirq/transformers/routing/route_circuit_cqc.py

@@ -245,17 +245,32 @@ def _get_one_and_two_qubit_ops_as_timesteps(
         The i'th entry in the nested two-qubit and single-qubit ops correspond to the two-qubit
         gates and single-qubit gates of the i'th timesteps respectively. When constructing the
         output routed circuit, single-qubit operations are inserted before two-qubit operations.
+
+        Raises:
+            ValueError: if circuit has intermediate measurement op's that act on three or more qubits and result is stored.
         """
         two_qubit_circuit = circuits.Circuit()
         single_qubit_ops: List[List[cirq.Operation]] = []
+        current_moment = 0
+
         for moment in circuit:
+            current_moment += 1
             for op in moment:
                 timestep = two_qubit_circuit.earliest_available_moment(op)
                 single_qubit_ops.extend([] for _ in range(timestep + 1 - len(single_qubit_ops)))
                 two_qubit_circuit.append(
                     circuits.Moment() for _ in range(timestep + 1 - len(two_qubit_circuit))
                 )
-                if protocols.num_qubits(op) == 2 and not protocols.is_measurement(op):
+                if protocols.num_qubits(op) > 2 and isinstance(op.gate, ops.MeasurementGate):
+                    if len(circuit.moments) == current_moment:
+                        single_qubit_ops[timestep].append(op)
+                    elif op.gate.key == "":
+                        single_qubit_ops[timestep] += [ops.measure(qubit) for qubit in op.qubits]
+                    else:
+                        raise ValueError(
+                            'Non-terminal measurements on three or more qubits when result is stored are not supported'
+                        )
+                elif protocols.num_qubits(op) == 2:
                     two_qubit_circuit[timestep] = two_qubit_circuit[timestep].with_operation(op)
                 else:
                     single_qubit_ops[timestep].append(op)

cirq-core/cirq/transformers/routing/route_circuit_cqc_test.py

@@ -107,6 +107,53 @@ def test_circuit_with_measurement_gates():
     cirq.testing.assert_same_circuits(routed_circuit, circuit)
 
 
+def test_circuit_with_two_qubit_intermediate_measurement_gate():
+    device = cirq.testing.construct_ring_device(2)
+    device_graph = device.metadata.nx_graph
+    router = cirq.RouteCQC(device_graph)
+    q = cirq.LineQubit.range(2)
+    hard_coded_mapper = cirq.HardCodedInitialMapper({q[i]: q[i] for i in range(2)})
+    circuit = cirq.Circuit(cirq.measure_each(*q), cirq.H.on_each(q))
+    routed_circuit = router(
+        circuit, initial_mapper=hard_coded_mapper, context=cirq.TransformerContext(deep=True)
+    )
+    device.validate_circuit(routed_circuit)
+
+
+def test_circuit_with_multi_qubit_intermediate_measurement_gate_and_result_not_stored():
+    device = cirq.testing.construct_ring_device(3)
+    device_graph = device.metadata.nx_graph
+    router = cirq.RouteCQC(device_graph)
+    q = cirq.LineQubit.range(3)
+    hard_coded_mapper = cirq.HardCodedInitialMapper({q[i]: q[i] for i in range(3)})
+    circuit = cirq.Circuit(
+        [cirq.Moment(cirq.MeasurementGate(3).on(*q)), cirq.Moment(cirq.H.on_each(q))]
+    )
+    routed_circuit = router(
+        circuit, initial_mapper=hard_coded_mapper, context=cirq.TransformerContext(deep=True)
+    )
+    expected = cirq.Circuit(
+        [
+            cirq.Moment(cirq.measure(q[0]), cirq.measure(q[1]), cirq.measure(q[2])),
+            cirq.Moment(cirq.H.on_each(q)),
+        ]
+    )
+    cirq.testing.assert_same_circuits(routed_circuit, expected)
+
+
+def test_circuit_with_multi_qubit_intermediate_measurement_gate_and_result_stored():
+    device = cirq.testing.construct_ring_device(3)
+    device_graph = device.metadata.nx_graph
+    router = cirq.RouteCQC(device_graph)
+    q = cirq.LineQubit.range(3)
+    hard_coded_mapper = cirq.HardCodedInitialMapper({q[i]: q[i] for i in range(3)})
+    circuit = cirq.Circuit(cirq.MeasurementGate(3, key="key").on(*q), cirq.H.on_each(*q))
+    with pytest.raises(ValueError):
+        _ = router(
+            circuit, initial_mapper=hard_coded_mapper, context=cirq.TransformerContext(deep=True)
+        )
+
+
 def test_circuit_with_non_unitary_and_global_phase():
     device = cirq.testing.construct_ring_device(4)
     device_graph = device.metadata.nx_graph

docs/dev/development.md

@@ -150,7 +150,7 @@ See the previous section for instructions.
 If you want to pip install cirq in an editable fashion, you'll have to install it per module, e.g.: 
 
 ```
-pip install -e ./cirq-core -e ./cirq-google -e ./cirq-ionq -e ./cirq-aqt
+pip install -e . ./cirq-core -e ./cirq-google -e ./cirq-ionq -e ./cirq-aqt ./cirq-ft ./cirq-pasqal ./cirq-rigetti ./cirq-web
 ```
 
 Note that `pip install -e .` will install the `cirq` metapackage only, and your code changes won't 

docs/transform/routing_transformer.ipynb

@@ -75,7 +75,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "metadata": {
     "id": "EJcUPXkY0K93"
    },
@@ -145,11 +145,27 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 2,
    "metadata": {
     "id": "NafLVgAD34IL"
    },
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "      ┌──┐\n",
+      "0: ────X─────X───@───────X───\n",
+      "       │         │       │\n",
+      "1: ────┼@────@───X───H───@───\n",
+      "       ││    │\n",
+      "2: ────@┼────X───────H───X───\n",
+      "        │                │\n",
+      "3: ─────X────────────────@───\n",
+      "      └──┘\n"
+     ]
+    }
+   ],
    "source": [
     "# The circuit to be routed\n",
     "q = cirq.LineQubit.range(4)\n",
@@ -183,11 +199,27 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 4,
    "metadata": {
     "id": "NO1dyRbS9-1x"
    },
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "           ┌──┐               ┌──┐\n",
+      "(1, 5): ────X─────X────────────@─────────X───\n",
+      "            │                  │         │\n",
+      "(2, 4): ────┼@────@───────×────┼X────────┼───\n",
+      "            ││    │       │    ││        │\n",
+      "(2, 5): ────@┼────X───H───×────X┼────H───@───\n",
+      "             │                  │\n",
+      "(3, 4): ─────X──────────────────@────────────\n",
+      "           └──┘               └──┘\n"
+     ]
+    }
+   ],
    "source": [
     "routed_circuit = router(circuit)\n",
     "print(routed_circuit)"
@@ -240,11 +272,19 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 5,
    "metadata": {
     "id": "DU8lHNiK4eCL"
    },
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "cirq.HardCodedInitialMapper({cirq.LineQubit(0): cirq.GridQubit(3, 5), cirq.LineQubit(1): cirq.GridQubit(3, 4), cirq.LineQubit(2): cirq.GridQubit(2, 5), cirq.LineQubit(3): cirq.GridQubit(2, 4)})\n"
+     ]
+    }
+   ],
    "source": [
     "# Use a hard-coded initial mapping strategy of logical to physical that places q0, q1, q2, q3 onto\n",
     "# Grid(3, 5), Grid(3, 6), Grid(4, 5), Grid(4, 6), respectively\n",
@@ -257,11 +297,27 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 6,
    "metadata": {
     "id": "RMGa1h2uoKui"
    },
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "           ┌──┐\n",
+      "(2, 4): ─────X───────────────────────────────────────────@───────────\n",
+      "             │                                           │\n",
+      "(2, 5): ────@┼───────────────────────────────────X───H───X───────────\n",
+      "            ││                                   │\n",
+      "(3, 4): ────┼@────────×[cirq.RoutingSwapTag()]───┼───@───────────X───\n",
+      "            │         │                          │   │           │\n",
+      "(3, 5): ────X─────X───×──────────────────────────@───X───────H───@───\n",
+      "           └──┘\n"
+     ]
+    }
+   ],
    "source": [
     "routed_circuit = router(circuit, lookahead_radius = 5, tag_inserted_swaps=True, initial_mapper=hc_initial_mapper)\n",
     "print(routed_circuit)"
@@ -465,6 +521,18 @@
   "kernelspec": {
    "display_name": "Python 3",
    "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.11.5"
   }
  },
  "nbformat": 4,