Bugfix/allow implicit swaps not handled correctly

docs/changelog.md

@@ -9,6 +9,7 @@
 - Use QIR by default for program submission.
 - Update pytket-qir version requirement to 0.15.
 - Add new `kwarg` `n_leakage_detection_qubits` to `process_circuits()`
+- Fix `allow_implicit_swaps` configuration not handled correctly in default passes.
 
 ## 0.38.1 (October 2024)
 

pytket/extensions/quantinuum/backends/quantinuum.py

@@ -684,10 +684,19 @@ def default_compilation_pass(self, optimisation_level: int = 2) -> BasePass:
         elif target_2qb_gate == OpType.ZZPhase:
             decomposition_passes = [
                 NormaliseTK2(),
-                DecomposeTK2(ZZPhase_fidelity=1.0),
+                DecomposeTK2(
+                    allow_swaps=self.compilation_config.allow_implicit_swaps,
+                    ZZPhase_fidelity=1.0,
+                ),
             ]
         elif target_2qb_gate == OpType.ZZMax:
-            decomposition_passes = [NormaliseTK2(), DecomposeTK2(ZZMax_fidelity=1.0)]
+            decomposition_passes = [
+                NormaliseTK2(),
+                DecomposeTK2(
+                    allow_swaps=self.compilation_config.allow_implicit_swaps,
+                    ZZMax_fidelity=1.0,
+                ),
+            ]
         else:
             raise ValueError(
                 f"Unrecognized target 2-qubit gate: {target_2qb_gate.name}"
@@ -711,7 +720,12 @@ def default_compilation_pass(self, optimisation_level: int = 2) -> BasePass:
                 ]
             )
         else:
-            passlist.append(FullPeepholeOptimise(target_2qb_gate=OpType.TK2))
+            passlist.append(
+                FullPeepholeOptimise(
+                    allow_swaps=self.compilation_config.allow_implicit_swaps,
+                    target_2qb_gate=OpType.TK2,
+                )
+            )
             passlist.extend(decomposition_passes)
             passlist.extend(
                 [

tests/unit/convert_test.py

@@ -183,6 +183,32 @@ def test_switch_target_2qb_gate() -> None:
     assert compiled.n_gates_of_type(OpType.TK2) == 0
 
 
+def test_not_allow_implicit_swaps() -> None:
+    # https://github.com/CQCL/pytket-quantinuum/issues/515
+    b = QuantinuumBackend("", machine_debug=True)
+    circuits = [Circuit(2).SWAP(0, 1), Circuit(2).CX(0, 1).CX(1, 0).CX(0, 1)]
+    b.set_compilation_config_allow_implicit_swaps(False)
+    for target_gate in [OpType.ZZMax, OpType.ZZPhase, OpType.TK2]:
+        for c in circuits:
+            b.set_compilation_config_target_2qb_gate(target_gate)
+            d0 = b.get_compiled_circuit(c, optimisation_level=0)
+            d1 = b.get_compiled_circuit(c, optimisation_level=1)
+            d2 = b.get_compiled_circuit(c, optimisation_level=2)
+            assert d0.implicit_qubit_permutation() == {
+                Qubit(0): Qubit(0),
+                Qubit(1): Qubit(1),
+            }
+            assert d1.implicit_qubit_permutation() == {
+                Qubit(0): Qubit(0),
+                Qubit(1): Qubit(1),
+            }
+            assert d2.implicit_qubit_permutation() == {
+                Qubit(0): Qubit(0),
+                Qubit(1): Qubit(1),
+            }
+
+
 if __name__ == "__main__":
     test_implicit_swap_removal()
     test_switch_target_2qb_gate()
+    test_not_allow_implicit_swaps()