Allow setting noise on measurement operation and apply it accordingly (…

…NVIDIA#2447) Signed-off-by: Thien Nguyen <[email protected]>
bmhowe23 · Dec 4, 2024 · f7a0b12 · f7a0b12
1 parent f433d74
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diff --git a/runtime/common/NoiseModel.h b/runtime/common/NoiseModel.h
@@ -256,7 +256,7 @@ class noise_model {
   std::unordered_map<std::string, PredicateFuncTy> gatePredicates;
 
   static constexpr const char *availableOps[] = {
-      "x", "y", "z", "h", "s", "t", "rx", "ry", "rz", "r1", "u3"};
+      "x", "y", "z", "h", "s", "t", "rx", "ry", "rz", "r1", "u3", "mz"};
 
 public:
   /// @brief default constructor

diff --git a/runtime/nvqir/CircuitSimulator.h b/runtime/nvqir/CircuitSimulator.h
@@ -1315,6 +1315,12 @@ class CircuitSimulatorBase : public CircuitSimulator {
     // Flush the Gate Queue
     flushGateQueue();
 
+    // Apply measurement noise (if any)
+    // Note: gate noises are applied during flushGateQueue
+    if (executionContext && executionContext->noiseModel)
+      applyNoiseChannel(/*gateName=*/"mz", /*controls=*/{},
+                        /*targets=*/{qubitIdx}, /*params=*/{});
+
     // If sampling, just store the bit, do nothing else.
     if (handleBasicSampling(qubitIdx, registerName))
       return true;

diff --git a/unittests/integration/noise_tester.cpp b/unittests/integration/noise_tester.cpp
@@ -641,3 +641,44 @@ CUDAQ_TEST(NoiseTest, checkCustomOperation) {
   }
 }
 #endif
+
+#if defined(CUDAQ_BACKEND_DM) || defined(CUDAQ_BACKEND_STIM)
+
+CUDAQ_TEST(NoiseTest, checkMeasurementNoise) {
+  cudaq::set_random_seed(13);
+  constexpr double bitFlipRate = 0.1;
+  cudaq::bit_flip_channel bf(bitFlipRate);
+  cudaq::noise_model noise;
+  // 10% bit flipping during measurement
+  noise.add_channel("mz", {0}, bf);
+  cudaq::set_noise(noise);
+  {
+    auto kernel = []() {
+      cudaq::qubit q;
+      x(q);
+      mz(q);
+    };
+    auto counts = cudaq::sample(10000, kernel);
+    counts.dump();
+    // Due to measurement errors, we have both 0/1 results.
+    EXPECT_EQ(2, counts.size());
+    EXPECT_NEAR(counts.probability("0"), bitFlipRate, 0.01);
+    EXPECT_NEAR(counts.probability("1"), 1.0 - bitFlipRate, 0.01);
+  }
+  {
+    auto kernel = []() {
+      cudaq::qvector q(2);
+      x(q);
+      mz(q);
+    };
+    auto counts = cudaq::sample(10000, kernel);
+    counts.dump();
+    // We only have measurement noise on the first qubit.
+    EXPECT_EQ(2, counts.size());
+    EXPECT_NEAR(counts.probability("01"), bitFlipRate, 0.01);
+    EXPECT_NEAR(counts.probability("11"), 1.0 - bitFlipRate, 0.01);
+  }
+  cudaq::unset_noise(); // clear for subsequent tests
+}
+
+#endif