✨ Add missing BQSKit RL synthesis actions

CHANGELOG.md

@@ -12,6 +12,8 @@ releases may include breaking changes.
 
 ### Added
 
+- ✨ Add BQSKit's `QSDPass` to the RL synthesis actions ([#795])
+  ([**@flowerthrower**])
 - ✨ Add Qiskit's `TrivialLayout`, `ElidePermutations`, `SabreSwap`,
   `BasicSwap`, `LookaheadSwap`, `RemoveIdentityEquivalent`, and
   `Optimize1qGatesSimpleCommutation` passes and the optional IBM-backed
@@ -100,6 +102,7 @@ for previous changelogs._
 
 [#773]: https://github.com/munich-quantum-toolkit/predictor/pull/771
 [#769]: https://github.com/munich-quantum-toolkit/predictor/pull/769
+[#795]: https://github.com/munich-quantum-toolkit/predictor/pull/795
 [#794]: https://github.com/munich-quantum-toolkit/predictor/pull/794
 [#758]: https://github.com/munich-quantum-toolkit/predictor/pull/758
 [#755]: https://github.com/munich-quantum-toolkit/predictor/pull/755

UPGRADING.md

@@ -67,7 +67,8 @@ The new actions include:
 - the `GeneralizedSabreRoutingPass` routing action;
 - the `BQSKitSABREMapping` mapping action; and
 - the `QSearchSynthesisPass`, `LEAPSynthesisPass`, `WalshDiagonalSynthesisPass`,
-  `FullQSDPass`, `BlockZXZPass`, and `FullBlockZXZPass` synthesis actions.
+  `QSDPass`, `FullQSDPass`, `BlockZXZPass`, and `FullBlockZXZPass` synthesis
+  actions.
 
 See the
 [framework setup](docs/setup.md#step-2-train-reinforcement-learning-models) for

src/mqt/predictor/rl/actions/bqskit_actions.py

@@ -15,7 +15,7 @@
 from functools import cache
 from typing import TYPE_CHECKING, TypeAlias, cast
 
-from bqskit import MachineModel
+from bqskit import Circuit, MachineModel
 from bqskit.compiler import Compiler, Workflow
 from bqskit.compiler.compile import (
     build_multi_qudit_retarget_workflow,
@@ -39,11 +39,13 @@
     IfThenElsePass,
     LEAPSynthesisPass,
     ManyQuditGatesPredicate,
+    QSDPass,
     QSearchSynthesisPass,
     RestoreMeasurements,
     SetModelPass,
     SetRandomSeedPass,
     StaticPlacementPass,
+    SynthesisPass,
     TrivialPlacementPass,
     UnfoldPass,
     WalshDiagonalSynthesisPass,
@@ -59,11 +61,11 @@
 if TYPE_CHECKING:
     from collections.abc import Callable
 
-    from bqskit import Circuit
     from bqskit.compiler.basepass import BasePass
     from bqskit.compiler.passdata import PassData
     from bqskit.compiler.workflow import WorkflowLike
     from bqskit.ir import Gate
+    from bqskit.qis import StateSystem, StateVector, UnitaryMatrix
     from qiskit import QuantumCircuit
     from qiskit.circuit import Qubit as QiskitQubit
     from qiskit.transpiler import Target
@@ -81,6 +83,22 @@
 _BQSKIT_NUM_WORKERS = 1 if os.getenv("GITHUB_ACTIONS") == "true" else -1
 
 
+class _QSDUnitarySynthesisPass(SynthesisPass):
+    """Apply one QSD level to each multi-qubit synthesis target."""
+
+    async def synthesize(
+        self,
+        target: UnitaryMatrix | StateVector | StateSystem,
+        data: PassData,
+    ) -> Circuit:
+        """Synthesize a partition target with one QSD level."""
+        del data
+        unitary = cast("UnitaryMatrix", target)
+        if unitary.num_qudits == 1:
+            return Circuit.from_unitary(unitary)
+        return QSDPass.qsd(unitary)
+
+
 def _r_gate(theta: float, phi: float) -> Instruction:
     """Construct an RGate with the given parameters."""
     return RGate(theta, phi)
@@ -309,6 +327,12 @@ def bqskit_synthesis_actions() -> list[Action]:
                 IfThenElsePass(DiagonalPredicate(1e-9), WalshDiagonalSynthesisPass()),
             ),
         ),
+        DeferredDeviceAction(
+            "QSDPass",
+            CompilationOrigin.BQSKIT,
+            PassType.SYNTHESIS,
+            transpile_pass=lambda device: _bqskit_partitioned_synthesis_factory(device, _QSDUnitarySynthesisPass()),
+        ),
         DeferredDeviceAction(
             "FullQSDPass",
             CompilationOrigin.BQSKIT,

tests/compilation/test_integration_further_SDKs.py

@@ -10,9 +10,12 @@
 
 from __future__ import annotations
 
+import asyncio
 from typing import TYPE_CHECKING
 
 import pytest
+from bqskit.compiler.passdata import PassData
+from bqskit.ir.gates import MPRYGate, MPRZGate, VariableUnitaryGate
 from mqt.bench.targets import get_device
 from qiskit import QuantumCircuit
 from qiskit.circuit import StandardEquivalenceLibrary
@@ -26,7 +29,7 @@
     TrivialLayout,
 )
 
-from mqt.predictor.rl.actions import CompilationOrigin, PassType
+from mqt.predictor.rl.actions import CompilationOrigin, PassType, bqskit_actions
 from mqt.predictor.rl.predictorenv import PredictorEnv
 
 if TYPE_CHECKING:
@@ -126,6 +129,22 @@ def env(target: Target) -> PredictorEnv:
     return PredictorEnv(device=target, reward_function="expected_fidelity")
 
 
+@pytest.mark.filterwarnings("ignore:__array__ implementation doesn't accept a copy keyword:DeprecationWarning")
+def test_qsd_unitary_synthesis_pass_applies_one_qsd_level(simple_circuit: QuantumCircuit) -> None:
+    """The QSD adapter performs one equivalent decomposition of a reachable partition target."""
+    bqskit_circuit = bqskit_actions.qiskit_to_bqskit(simple_circuit)
+    unitary = bqskit_circuit.get_unitary()
+    synthesis_pass = bqskit_actions._QSDUnitarySynthesisPass()  # ruff: ignore[private-member-access]
+
+    decomposed = asyncio.run(synthesis_pass.synthesize(unitary, PassData(bqskit_circuit)))
+
+    assert decomposed.get_unitary().get_distance_from(unitary) < 1e-7
+    assert sum(count for gate, count in decomposed.gate_counts.items() if isinstance(gate, VariableUnitaryGate)) == 4
+    assert all(gate.num_qudits == 2 for gate in decomposed.gate_set if isinstance(gate, VariableUnitaryGate))
+    assert sum(count for gate, count in decomposed.gate_counts.items() if isinstance(gate, MPRZGate)) == 2
+    assert sum(count for gate, count in decomposed.gate_counts.items() if isinstance(gate, MPRYGate)) == 1
+
+
 def test_synthesis_actions_produce_native_gates(
     simple_circuit: QuantumCircuit,
     env: PredictorEnv,