[rt] Fix #1215

runtime/cudaq/qis/managers/BasicExecutionManager.h

@@ -198,7 +198,22 @@ class BasicExecutionManager : public cudaq::ExecutionManager {
     for (auto &t : targets)
       mutable_targets.push_back(t);
 
-    if (isAdjoint || !adjointQueueStack.empty()) {
+    // We need to check if we need take the adjoint of the operation. To do this
+    // we use a logical XOR between `isAdjoint` and whether the size of
+    // `adjointQueueStack` is even. The size of `adjointQueueStack` corresponds
+    // to the number of nested `cudaq::adjoint` calls. If the size is even, then
+    // we need to change the operation when `isAdjoint` is true. If the size is
+    // odd, then we need to change the operation when `isAdjoint` is false.
+    // (Adjoint modifiers cancel each other, e.g, `adj adj r1` is `r1`.)
+    //
+    // The cases:
+    //  * not-adjoint, even number of `cudaq::adjoint` => _no_ need to change op
+    //  * not-adjoint, odd number of `cudaq::adjoint`  => change op
+    //  * adjoint,     even number of `cudaq::adjoint` => change op
+    //  * adjoint,     odd number `cudaq::adjoint`     => _no_ need to change op
+    //
+    //  N.B: the `!!` is to force the result into a boolean value.
+    if (isAdjoint != !!(adjointQueueStack.size() % 2)) {
       for (std::size_t i = 0; i < params.size(); i++)
         mutable_params[i] = -1.0 * params[i];
       if (gateName == "t")

unittests/integration/adjoint_tester.cpp

@@ -218,3 +218,39 @@ CUDAQ_TEST(AdjointTester, checkNestedAdjoint) {
   // ctrl ry pi / 4 1 2
   // }
 }
+
+// From issue: https://github.com/NVIDIA/cuda-quantum/issues/1215
+
+__qpu__ void foo(cudaq::qubit &q) { rz<cudaq::adj>(M_PI_2, q); }
+
+__qpu__ void bar() {
+  cudaq::qubit q;
+  rz<cudaq::adj>(M_PI_2, q);
+  cudaq::adjoint(foo, q);
+}
+
+CUDAQ_TEST(AdjointTester, checkEvenAdjointNesting) {
+  auto result = cudaq::get_state(bar);
+  auto amplitudes = result.get_data();
+  std::array<std::complex<double>, 2> expected = {1., 0};
+  EXPECT_EQ(expected[0], amplitudes[0]);
+  EXPECT_EQ(expected[1], amplitudes[1]);
+}
+
+__qpu__ void zaz(cudaq::qubit &q) { rz<cudaq::adj>(M_PI_2, q); }
+
+__qpu__ void foo_2(cudaq::qubit &q) { cudaq::adjoint(zaz, q); }
+
+__qpu__ void bar_2() {
+  cudaq::qubit q;
+  rz(M_PI_2, q);
+  cudaq::adjoint(foo_2, q);
+}
+
+CUDAQ_TEST(AdjointTester, checkOddAdjointNesting) {
+  auto result = cudaq::get_state(bar_2);
+  auto amplitudes = result.get_data();
+  std::array<std::complex<double>, 2> expected = {1., 0};
+  EXPECT_EQ(expected[0], amplitudes[0]);
+  EXPECT_EQ(expected[1], amplitudes[1]);
+}