fix of dit compiler edge case

src/mqt/qudits/compiler/dit_compiler.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import typing
+from typing import Optional
 
 from ..core.lanes import Lanes
 from ..quantum_circuit.components.extensions.gate_types import GateTypes
@@ -47,9 +48,12 @@ def compile(self, backend: Backend, circuit: QuantumCircuit, passes_names: list[
             elif "Multi" in str(compiler_pass):
                 passes_dict[GateTypes.MULTI] = decomposition
         for gate in circuit.instructions:
-            decomposer = typing.cast(CompilerPass, passes_dict.get(gate.gate_type))
-            new_instructions = decomposer.transpile_gate(gate)
-            new_instr.extend(new_instructions)
+            decomposer = typing.cast(Optional[CompilerPass], passes_dict.get(gate.gate_type))
+            if decomposer is not None:
+                new_instructions = decomposer.transpile_gate(gate)
+                new_instr.extend(new_instructions)
+            else:
+                new_instr.append(gate)
 
         circuit.set_instructions(new_instr)
         circuit.set_mapping([graph.log_phy_map for graph in backend.energy_level_graphs])

test/python/compiler/twodit/entangled_qr/test_entangled_qr.py

@@ -41,3 +41,33 @@ def test_entangling_qr(self):
         target /= target[0][0]
         res = (abs(target - np.identity(15, dtype="complex")) < 10e-5).all()
         assert res
+
+    @staticmethod
+    def test_entangling_qr_2():
+        # Create the original circuit
+        circuit = QuantumCircuit(2, [3, 3], 0)
+        circuit.x(0)
+        circuit.csum([0, 1])
+
+        # Simulate the original circuit
+        original_state = circuit.simulate()
+        print("Original circuit simulation result:")
+        print(original_state.round(3))
+
+        # Set up the provider and backend
+        provider = MQTQuditProvider()
+        backend_ion = provider.get_backend("faketraps2trits")
+
+        # Compile the circuit
+        qudit_compiler = QuditCompiler()
+        passes = ["LogEntQRCEXPass"]
+        new_circuit = qudit_compiler.compile(backend_ion, circuit, passes)
+
+        # Simulate the compiled circuit
+        compiled_state = new_circuit.simulate()
+        print("\nCompiled circuit simulation result:")
+        print(compiled_state.round(3))
+
+        # Compare the results
+        is_close = np.allclose(original_state, compiled_state)
+        print(f"\nAre the simulation results close? {is_close}")