fix directed ECR gate (#318)

* add directed routing, predicate and update changelog

* Update docs/changelog.rst

Co-authored-by: Alec Edgington <54802828+cqc-alec@users.noreply.github.com>

* Update pytket/extensions/qiskit/backends/ibm.py

Co-authored-by: Alec Edgington <54802828+cqc-alec@users.noreply.github.com>

* update predicate construction

* update testcase, reorder predicates

---------

Co-authored-by: Alec Edgington <54802828+cqc-alec@users.noreply.github.com>

docs/changelog.rst

@@ -5,6 +5,8 @@ Unreleased
 ----------
 
 * Add `IBMQBackend.default_compilation_pass_static` for offline compilation given config and props objects.
+* Add `DirectednessPredicate` to IBMQBackend
+* Default compilation pass of IBMQBackend will keep ECR gates in the direction required by the backend.
 
 0.51.1rc0 (April 2024)
 ----------------------

pytket/extensions/qiskit/backends/ibm.py

@@ -82,11 +82,12 @@
     NoFastFeedforwardPredicate,
     MaxNQubitsPredicate,
     Predicate,
+    DirectednessPredicate,
 )
 from qiskit.providers.models import BackendProperties, QasmBackendConfiguration  # type: ignore
 
 from ..qiskit_convert import tk_to_qiskit, _tk_gate_set
-from pytket.architecture import FullyConnected
+from pytket.architecture import FullyConnected, Architecture
 from pytket.placement import NoiseAwarePlacement
 from pytket.utils import prepare_circuit
 from pytket.utils.outcomearray import OutcomeArray
@@ -346,17 +347,16 @@ def required_predicates(self) -> List[Predicate]:
                 )
             ),
         ]
+        if isinstance(self.backend_info.architecture, Architecture):
+            predicates.append(DirectednessPredicate(self.backend_info.architecture))
+
         mid_measure = self._backend_info.supports_midcircuit_measurement
         fast_feedforward = self._backend_info.supports_fast_feedforward
         if not mid_measure:
-            predicates = [
-                NoClassicalControlPredicate(),
-                NoMidMeasurePredicate(),
-            ] + predicates
+            predicates.append(NoClassicalControlPredicate())
+            predicates.append(NoMidMeasurePredicate())
         if not fast_feedforward:
-            predicates = [
-                NoFastFeedforwardPredicate(),
-            ] + predicates
+            predicates.append(NoFastFeedforwardPredicate())
         return predicates
 
     def default_compilation_pass(
@@ -451,7 +451,7 @@ def default_compilation_pass_offline(
                 CXMappingPass(
                     arch,
                     noise_aware_placement,
-                    directed_cx=False,
+                    directed_cx=True,
                     delay_measures=(not mid_measure),
                 )
             )

tests/backend_test.py

@@ -476,7 +476,8 @@ def test_nshots(
         circuit = Circuit(1).X(0)
         circuit.measure_all()
         n_shots = [1, 2, 3]
-        results = b.get_results(b.process_circuits([circuit] * 3, n_shots=n_shots))
+        circ_comp = b.get_compiled_circuit(circuit)
+        results = b.get_results(b.process_circuits([circ_comp] * 3, n_shots=n_shots))
         assert [sum(r.get_counts().values()) for r in results] == n_shots
 
 
@@ -1330,6 +1331,21 @@ def test_crosstalk_noise_model() -> None:
     res.get_counts()
 
 
+@pytest.mark.skipif(skip_remote_tests, reason=REASON)
+def test_ecr(ibm_brisbane_backend: IBMQBackend) -> None:
+    ghz5 = Circuit(5)
+    ghz5.H(0).CX(0, 1).CX(0, 2).CX(0, 3).CX(0, 4)
+    ghz5.measure_all()
+    ibm_ghz5 = ibm_brisbane_backend.get_compiled_circuit(ghz5)
+
+    compiled_ghz5 = ibm_brisbane_backend.get_compiled_circuit(ibm_ghz5)
+
+    ibm_brisbane_backend.valid_circuit(compiled_ghz5)
+
+    handle = ibm_brisbane_backend.process_circuit(compiled_ghz5, n_shots=1000)
+    ibm_brisbane_backend.cancel(handle)
+
+
 # helper function for testing
 def _get_qiskit_statevector(qc: QuantumCircuit) -> np.ndarray:
     """Given a QuantumCircuit, use aer_simulator_statevector to compute its