Wrapping up mirror circuit impl

As the first prototype, I only expose a single flag to enable validation if NISQ kernel execution.

If enabled, kernel execution (NISQ) will be accompanied by Pauli-randomized mirror circuits to determine if the backend can produce the expected readout.
Signed-off-by: Thien Nguyen <nguyentm@ornl.gov>

examples/mirror_validation/noise_model.json

+{
+  "errors": [
+    {
+      "type": "qerror",
+      "operations": [
+        "u1"
+      ],
+      "instructions": [
+        [
+          {
+            "name": "x",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "id",
+            "qubits": [
+              0
+            ]
+          }
+        ]
+      ],
+      "probabilities": [
+        0.00025,
+        0.00025,
+        0.00025,
+        0.99925
+      ]
+    },
+    {
+      "type": "qerror",
+      "operations": [
+        "u2"
+      ],
+      "instructions": [
+        [
+          {
+            "name": "x",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "id",
+            "qubits": [
+              0
+            ]
+          }
+        ]
+      ],
+      "probabilities": [
+        0.00025,
+        0.00025,
+        0.00025,
+        0.99925
+      ]
+    },
+    {
+      "type": "qerror",
+      "operations": [
+        "u3"
+      ],
+      "instructions": [
+        [
+          {
+            "name": "x",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "id",
+            "qubits": [
+              0
+            ]
+          }
+        ]
+      ],
+      "probabilities": [
+        0.00025,
+        0.00025,
+        0.00025,
+        0.99925
+      ]
+    },
+    {
+      "type": "qerror",
+      "operations": [
+        "cx"
+      ],
+      "instructions": [
+        [
+          {
+            "name": "x",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              0
+            ]
+          }
+        ],
+        [
+          {
+            "name": "x",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "x",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "x",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "x",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "x",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "x",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "y",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "y",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "y",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "x",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "z",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "y",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "z",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "z",
+            "qubits": [
+              0
+            ]
+          },
+          {
+            "name": "z",
+            "qubits": [
+              1
+            ]
+          }
+        ],
+        [
+          {
+            "name": "id",
+            "qubits": [
+              0
+            ]
+          }
+        ]
+      ],
+      "probabilities": [
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.0006250000000000001,
+        0.9906250000000001
+      ]
+    }
+  ]
+}
\ No newline at end of file

examples/mirror_validation/validate_execution.cpp

+// Compile to run with validation mode: 
+// Qpp (noiseless)
+// qcor -validate validate_execution.cpp -shots 1024
+// Aer (noisy)
+// qcor -validate validate_execution.cpp -shots 1024 -qpu aer[noise-model:noise_model.json]
+__qpu__ void noisy_zero(qreg q, int cx_count) {
+  H(q);
+  for (int i = 0; i < cx_count; i++) {
+    X::ctrl(q[0], q[1]);
+  }
+  H(q);
+  Measure(q);
+}
+
+int main() {
+  // qcor::set_verbose(true);
+  // On the noisy simulator, the validation will be successful for 1 cycle
+  // but will probably fail when running with 10 cycles.
+  const int nb_cycles = 1;
+  // const int nb_cycles = 10;
+  auto q = qalloc(2);
+  noisy_zero(q, nb_cycles);
+  q.print();
+}
\ No newline at end of file

lib/mirror_rb/mirror_circuit_rb.cpp

@@ -4,10 +4,27 @@
 #include "qcor_ir.hpp"
 #include "qcor_pimpl_impl.hpp"
 #include "xacc.hpp"
+#include "xacc_plugin.hpp"
 #include "xacc_service.hpp"
 #include <cassert>
 #include <random>
-#include "xacc_plugin.hpp"
+namespace {
+std::vector<std::shared_ptr<xacc::Instruction>>
+getLayer(std::shared_ptr<xacc::CompositeInstruction> circuit, int layerId) {
+  std::vector<std::shared_ptr<xacc::Instruction>> result;
+  assert(layerId < circuit->depth());
+  auto graphView = circuit->toGraph();
+  for (int i = 1; i < graphView->order() - 1; i++) {
+    auto node = graphView->getVertexProperties(i);
+    if (node.get<int>("layer") == layerId) {
+      result.emplace_back(
+          circuit->getInstruction(node.get<std::size_t>("id") - 1)->clone());
+    }
+  }
+  assert(!result.empty());
+  return result;
+}
+} // namespace
 namespace xacc {
 namespace quantum {
 // Helper to convert a gate
@@ -76,7 +93,7 @@ public:
   }
 
   void visit(Measure &measure) override {
-    xacc::error("The mirror circuit must not contain measure gates.");
+    // Ignore measure
   }
 
   void visit(Identity &i) override {}
@@ -129,33 +146,42 @@ public:
     visit(ry2);
   }
 
-  std::shared_ptr<CompositeInstruction> getProgram() { return m_program; }
+  std::shared_ptr<CompositeInstruction> getProgram() { return balanceLayer(); }
 
 private:
+  std::shared_ptr<CompositeInstruction> balanceLayer() {
+    // Balance all layers
+    // The mirroring protocol doesn't work well when there are layers that has
+    // no gate on a qubit line, hence, just add an Identity there:
+    auto program = m_gateRegistry->createComposite("temp_composite");
+    const auto d = m_program->depth();
+    const auto nbQubits = m_program->nPhysicalBits();
+    for (int layer = 0; layer < d; ++layer) {
+      std::set<int> qubits;
+      auto current_layers = getLayer(m_program, layer);
+      for (const auto &gate : current_layers) {
+        program->addInstruction(gate);
+        for (const auto &bit : gate->bits()) {
+          qubits.emplace(bit);
+        }
+      }
+      if (qubits.size() < nbQubits) {
+        for (int i = 0; i < nbQubits; ++i) {
+          if (!xacc::container::contains(qubits, i)) {
+            program->addInstruction(
+                m_gateRegistry->createInstruction("U", {(size_t)i}, {0.0, 0.0, 0.0}));
+          }
+        }
+      }
+    }
+    return program;
+  }
   std::shared_ptr<CompositeInstruction> m_program;
   std::shared_ptr<xacc::IRProvider> m_gateRegistry;
 };
 } // namespace quantum
 } // namespace xacc
 
-namespace {
-std::vector<std::shared_ptr<xacc::Instruction>>
-getLayer(std::shared_ptr<xacc::CompositeInstruction> circuit, int layerId) {
-  std::vector<std::shared_ptr<xacc::Instruction>> result;
-  assert(layerId < circuit->depth());
-  auto graphView = circuit->toGraph();
-  for (int i = 1; i < graphView->order() - 1; i++) {
-    auto node = graphView->getVertexProperties(i);
-    if (node.get<int>("layer") == layerId) {
-      result.emplace_back(
-          circuit->getInstruction(node.get<std::size_t>("id") - 1)->clone());
-    }
-  }
-  assert(!result.empty());
-  return result;
-}
-} // namespace
-
 namespace qcor {
 std::pair<bool, xacc::HeterogeneousMap> MirrorCircuitValidator::validate(
     std::shared_ptr<xacc::Accelerator> qpu,
@@ -173,7 +199,7 @@ std::pair<bool, xacc::HeterogeneousMap> MirrorCircuitValidator::validate(
   if (options.keyExists<double>("epsilon")) {
     eps = options.get<double>("epsilon");
   }
-  
+
   qpu->updateConfiguration({{"shots", n_shots}});
   std::vector<double> trial_success_probs;
   auto provider = xacc::getIRProvider("quantum");
@@ -219,7 +245,8 @@ std::pair<bool, xacc::HeterogeneousMap> MirrorCircuitValidator::validate(
 }
 
 std::pair<std::shared_ptr<CompositeInstruction>, std::vector<bool>>
-MirrorCircuitValidator::createMirrorCircuit(std::shared_ptr<CompositeInstruction> in_circuit) {
+MirrorCircuitValidator::createMirrorCircuit(
+    std::shared_ptr<CompositeInstruction> in_circuit) {
   std::vector<std::shared_ptr<xacc::Instruction>> mirrorCircuit;
   auto gateProvider = xacc::getService<xacc::IRProvider>("quantum");
 

runtime/qcor.hpp

@@ -51,6 +51,9 @@ public:
 #endif
 #ifdef __internal__qcor__print__final__submission
     xacc::internal_compiler::__print_final_submission = true;
+#endif
+#ifdef __internal__qcor__validate__execution
+    xacc::internal_compiler::__validate_nisq_execution = true;
 #endif
   }
 };

runtime/qrt/impls/nisq/nisq_qrt.cpp

@@ -406,6 +406,24 @@ class NISQ : public ::quantum::QuantumRuntime,
       xacc::storeBuffer(xacc::as_shared_ptr(buffer));
       xacc::internal_compiler::execute(
           buffer, program->as_xacc());
+      if (__validate_nisq_execution) {
+        auto [validated, validationData] = validate_backend_execution(program);
+        if (!validated) {
+          std::cout << "Failed to validate the execution of the program on the "
+                    << get_qpu()->name() << " backend.\n";
+          // NOTES: currently, we validate the whole program (all layers),
+          // we can run layer-by-layer to determine at which depth the program
+          // starts to fail.
+          std::cout << "Result buffer:\n";
+          buffer->print();
+          throw std::logic_error(
+              "Failed to validate backend execution in validation mode.\n");
+        }
+        else {
+          std::cout << "Successfully validate the execution of the program on the "
+                    << get_qpu()->name() << " backend.\n";
+        }
+      }
     }
 
     clearProgram();

runtime/qrt/qrt.cpp

@@ -24,6 +24,7 @@ std::vector<int> __qubit_map = {};
 std::string __qrt_env = "nisq";
 bool __print_final_submission = false;
 std::string __print_final_submission_filename = "";
+bool __validate_nisq_execution = false;
 
 void execute_pass_manager(
     std::shared_ptr<qcor::CompositeInstruction> optional_composite) {

runtime/qrt/qrt.hpp

@@ -250,7 +250,8 @@ extern std::string __qrt_env;
 // Print final CompositeInstruction for backend submission
 extern bool __print_final_submission;
 extern std::string __print_final_submission_filename;
-
+// Backend execution validation
+extern bool __validate_nisq_execution;
 // Execute the pass manager on the provided kernel.
 // If none provided, execute the pass manager on the current QRT kernel.
 void execute_pass_manager(

tools/driver/qcor.in

@@ -348,6 +348,11 @@ def main(argv=None):
         parser.add_argument('-qs-runtime', metavar='', help='Specifies the classical capabilites of the QIR runtime. Valid options: BasicQuantumFunctionality, BasicMeasurementFeedback, FullComputation')
         parser.add_argument('-qdk-version', metavar='', help='Specifies the Microsoft Quantum SDK version to use.')
 
+        # Flag to enable validation:
+        # Currently, it means enabling Pauli-randomized mirror circuit benchmarking:
+        # i.e., executing a set of benchmarking circuits related to the original circuit that we know the expected bitstring
+        parser.add_argument('-validate', metavar='', help='Enables backend execution validation via the mirror circuit technique.')
+
         args = parser.parse_args(sys.argv)
 
     if '-pythonpath' in sys.argv[1:]:
@@ -608,6 +613,13 @@ def main(argv=None):
         if qrtName == 'ftqc': 
             sys.argv += ['-D_QCOR_FTQC_RUNTIME']
     
+    if '-validate' in sys.argv[1:]:
+        sys.argv.remove('-validate')
+        sys.argv += ['-D__internal__qcor__validate__execution']
+        if '-D_QCOR_FTQC_RUNTIME' in sys.argv:
+            print('Execution validation cannot be used with FTQC runtime.')
+            exit(1)
+
     # if not empty
     if '@QCOR_APPEND_PLUGIN_PATH@':
         sys.argv += ['-D__internal__qcor__compile__plugin__path=\"@QCOR_APPEND_PLUGIN_PATH@\"']