munich-quantum-toolkit · J4MMlE · Dec 28, 2025 · Jan 15, 2026 · Jan 22, 2026 · Jan 22, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning], with the exception that minor rel
 
 ### Added
 
+- ✨ Add a `mlir-merge-single-qubit-rotation-gates` pass for merging consecutive rotation gates using quaternions ([#1407]) ([**@J4MMlE**])
 - ✨ Add Sampler and Estimator Primitives to the QDMI-Qiskit Interface ([#1507]) ([**@marcelwa**])
 - ✨ Add conversions between Jeff and QCO ([#1479], [#1548], [#1565]) ([**@denialhaag**])
 - ✨ Add a `place-and-route` pass for mapping circuits to architectures with restricted topologies ([#1537], [#1547], [#1568]) ([**@MatthiasReumann**])
@@ -377,6 +378,7 @@ _📚 Refer to the [GitHub Release Notes](https://github.com/munich-quantum-tool
 [#1413]: https://github.com/munich-quantum-toolkit/core/pull/1413
 [#1412]: https://github.com/munich-quantum-toolkit/core/pull/1412
 [#1411]: https://github.com/munich-quantum-toolkit/core/pull/1411
+[#1407]: https://github.com/munich-quantum-toolkit/core/pull/1407
 [#1406]: https://github.com/munich-quantum-toolkit/core/pull/1406
 [#1403]: https://github.com/munich-quantum-toolkit/core/pull/1403
 [#1402]: https://github.com/munich-quantum-toolkit/core/pull/1402
@@ -533,6 +535,7 @@ _📚 Refer to the [GitHub Release Notes](https://github.com/munich-quantum-tool
 [**@lirem101**]: https://github.com/lirem101
 [**@Ectras**]: https://github.com/Ectras
 [**@simon1hofmann**]: https://github.com/simon1hofmann
+[**@J4MMlE**]: https://github.com/J4MMlE
 
 <!-- General links -->
 

diff --git a/mlir/include/mlir/Compiler/CompilerPipeline.h b/mlir/include/mlir/Compiler/CompilerPipeline.h
@@ -40,6 +40,9 @@ struct QuantumCompilerConfig {
 
   /// Print IR after each stage
   bool printIRAfterAllStages = false;
+
+  /// Enable quaternion-based rotation gate merging
+  bool mergeSingleQubitRotationGates = false;
 };
 
 /**

diff --git a/mlir/include/mlir/Dialect/QCO/Transforms/Passes.h b/mlir/include/mlir/Dialect/QCO/Transforms/Passes.h
@@ -21,11 +21,6 @@ namespace mlir::qco {
 #define GEN_PASS_DECL
 #include "mlir/Dialect/QCO/Transforms/Passes.h.inc" // IWYU pragma: export
 
-//===----------------------------------------------------------------------===//
-// Registration
-//===----------------------------------------------------------------------===//
-
-/// Generate the code for registering passes.
 #define GEN_PASS_REGISTRATION
 #include "mlir/Dialect/QCO/Transforms/Passes.h.inc" // IWYU pragma: export
 

diff --git a/mlir/include/mlir/Dialect/QCO/Transforms/Passes.td b/mlir/include/mlir/Dialect/QCO/Transforms/Passes.td
@@ -11,6 +11,17 @@
 
 include "mlir/Pass/PassBase.td"
 
+def MergeRotationGates : Pass<"merge-rotation-gates", "mlir::ModuleOp"> {
+  let dependentDialects = ["mlir::qco::QCODialect",
+                           "::mlir::arith::ArithDialect",
+                           "::mlir::math::MathDialect"];
+  let summary = "Merge rotation gates using quaternion-based fusion";
+  let description = [{
+    Merges consecutive rotation gates of different types (rx, ry, rz, p, r, u2, u)
+    using quaternion representation and the Hamilton product.
+  }];
+}
+
 //===----------------------------------------------------------------------===//
 // Transpilation Passes
 //===----------------------------------------------------------------------===//

diff --git a/mlir/lib/Compiler/CMakeLists.txt b/mlir/lib/Compiler/CMakeLists.txt
@@ -20,6 +20,7 @@ add_mlir_library(
   MLIRQCToQCO
   MLIRQCOToQC
   MLIRQCToQIR
+  MLIRQCOTransforms
   MQT::MLIRSupport
   DISABLE_INSTALL)
 

diff --git a/mlir/lib/Compiler/CompilerPipeline.cpp b/mlir/lib/Compiler/CompilerPipeline.cpp
@@ -13,6 +13,7 @@
 #include "mlir/Conversion/QCOToQC/QCOToQC.h"
 #include "mlir/Conversion/QCToQCO/QCToQCO.h"
 #include "mlir/Conversion/QCToQIR/QCToQIR.h"
+#include "mlir/Dialect/QCO/Transforms/Passes.h"
 #include "mlir/Support/PrettyPrinting.h"
 
 #include <llvm/ADT/StringRef.h>
@@ -140,8 +141,11 @@ QuantumCompilerPipeline::runPipeline(ModuleOp module,
     }
   }
   // Stage 5: Optimization passes
-  // TODO: Add optimization passes
-  if (failed(runStage([&](PassManager& pm) { addCleanupPasses(pm); }))) {
+  if (failed(runStage([&](PassManager& pm) {
+        if (config_.mergeSingleQubitRotationGates) {
+          pm.addPass(mlir::qco::createMergeRotationGates());
+        }
+      }))) {
     return failure();
   }
   if (record != nullptr && config_.recordIntermediates) {

diff --git a/mlir/lib/Dialect/QCO/Transforms/CMakeLists.txt b/mlir/lib/Dialect/QCO/Transforms/CMakeLists.txt
@@ -15,7 +15,8 @@ add_mlir_library(
   PRIVATE
   MLIRQCODialect
   MLIRQCOUtils
-  ${dialect_libs}
+  MLIRArithDialect
+  MLIRMathDialect
   DEPENDS
   MLIRQCOTransformsIncGen)