Fix number of qubits in transpiled circuits (#113)

* fix append

* Use target qubits for transpiled circuit

* add definition of RZZ gate

* remove rzz gate support from target

* Fix hex string in bitarray

* fix get_counts returns binary string

Author: doichanj

CMakeLists.txt

@@ -82,6 +82,7 @@ endfunction()
 
 add_application(circuit_test tests/circuit_test.cpp)
 add_application(observable_test tests/observable_test.cpp)
+
 if(QRMI_ROOT)
   add_application(sampler_test tests/sampler_test.cpp)
   add_application(transpile_test tests/transpile_test.cpp)

src/circuit/quantumcircuit_def.hpp

@@ -28,6 +28,7 @@
 #include "circuit/quantumregister.hpp"
 #include "circuit/library/standard_gates/standard_gates.hpp"
 #include "circuit/circuitinstruction.hpp"
+#include "transpiler/target.hpp"
 
 #include <complex>
 #include "qiskit.h"
@@ -60,6 +61,7 @@ class QuantumCircuit {
   std::vector<ClassicalRegister> cregs_;
 
   std::shared_ptr<rust_circuit> rust_circuit_ = nullptr;
+  std::shared_ptr<transpiler::Target> target_ = nullptr;
 
   std::shared_ptr<ControlFlowOp> pending_control_flow_op_ = nullptr;
 public:
@@ -96,11 +98,23 @@ class QuantumCircuit {
 
   /// @brief Return number of qubits
   /// @return number of qubits
-  uint_t num_qubits(void) const { return num_qubits_; }
+  uint_t num_qubits(void) const
+  {
+    if (target_) {
+      return target_->num_qubits();
+    }
+    return num_qubits_;
+  }
 
   /// @brief Return number of classical bits
   /// @return number of classical bits
-  uint_t num_clbits(void) const { return num_clbits_; }
+  uint_t num_clbits(void) const
+  {
+    if (target_) {
+      return target_->num_qubits();
+    }
+    return num_clbits_;
+  }
 
   std::shared_ptr<rust_circuit> get_rust_circuit(const bool update = true)
   {
@@ -117,6 +131,11 @@ class QuantumCircuit {
   /// @param circ smart pointer to RUst circuit
   void from_rust_circuit(std::shared_ptr<rust_circuit> circ);
 
+  /// @brief set target to this circuit
+  /// @param target smart pointer to target
+  /// @details target is set for transpiled circuit
+  void set_target(std::shared_ptr<transpiler::Target> target);
+
   /// @brief set global phase
   /// @param phase global phase value
   void global_phase(const double phase);

src/circuit/quantumcircuit_impl.hpp

@@ -127,6 +127,7 @@ QuantumCircuit::QuantumCircuit(const QuantumCircuit& circ)
   cregs_ = circ.cregs_;
 
   rust_circuit_ = circ.rust_circuit_;
+  target_ = circ.target_;
 }
 
 QuantumCircuit QuantumCircuit::copy(void)
@@ -141,6 +142,8 @@ QuantumCircuit QuantumCircuit::copy(void)
   copied.qregs_ = qregs_;
   copied.cregs_ = cregs_;
 
+  copied.target_ = target_;
+
   return copied;
 }
 
@@ -169,8 +172,17 @@ QuantumCircuit::~QuantumCircuit()
   if (rust_circuit_){
     rust_circuit_.reset();
   }
+  if (target_) {
+    target_.reset();
+  }
+}
+
+void QuantumCircuit::set_target(std::shared_ptr<transpiler::Target> target)
+{
+  target_ = target;
 }
 
+
 void QuantumCircuit::get_qubits(reg_t& bits)
 {
   bits.clear();
@@ -1254,6 +1266,13 @@ std::string QuantumCircuit::to_qasm3(void)
           qasm3 << "  h _gate_q_1;" << std::endl;
           qasm3 << "}" << std::endl;
           break;
+        case QkGate_RZZ:
+          qasm3 << "gate rzz(p0) _gate_q_0, _gate_q_1 {" << std::endl;
+          qasm3 << "  cx _gate_q_0, _gate_q_1;" << std::endl;
+          qasm3 << "  rz(p0) _gate_q_1;" << std::endl;
+          qasm3 << "  cx _gate_q_0, _gate_q_1;" << std::endl;
+          qasm3 << "}" << std::endl;
+          break;
         case QkGate_RCCX:
           qasm3 << "gate rccx _gate_q_0, _gate_q_1, _gate_q_2 {" << std::endl;
           qasm3 << "  h _gate_q_2;" << std::endl;
@@ -1375,8 +1394,8 @@ std::string QuantumCircuit::to_qasm3(void)
   // registers
   std::string creg_name = "c";
   std::string qreg_name = "q";
-  qasm3 << "bit[" << num_clbits_ << "] " << creg_name << ";" << std::endl;
-  qasm3 << "qubit[" << num_qubits_ << "] " << qreg_name << ";" << std::endl;
+  qasm3 << "bit[" << num_clbits() << "] " << creg_name << ";" << std::endl;
+  qasm3 << "qubit[" << num_qubits() << "] " << qreg_name << ";" << std::endl;
 
   // save ops
   uint_t nops;

src/compiler/transpiler.hpp

@@ -34,7 +34,7 @@ namespace compiler {
 circuit::QuantumCircuit transpile(circuit::QuantumCircuit& circ, providers::BackendV2& backend, int optimization_level = 2, double approximation_degree = 1.0, int seed_transpiler = -1)
 {
   auto target = backend.target();
-  if (!target.is_set()) {
+  if (target == nullptr) {
     return circ;
   }
 
@@ -46,15 +46,18 @@ circuit::QuantumCircuit transpile(circuit::QuantumCircuit& circ, providers::Back
   QkTranspileResult result;
   char* error;
 
-  QkExitCode ret = qk_transpile(circ.get_rust_circuit().get(), target.rust_target(), &options, &result, &error);
+  QkExitCode ret = qk_transpile(circ.get_rust_circuit().get(), target->rust_target(), &options, &result, &error);
   if (ret != QkExitCode_Success) {
     std::cerr << "transpile error (" << ret << ") : "<< error << std::endl;
+    target.reset();
     return circ;
   }
   circuit::QuantumCircuit transpiled;
   transpiled.from_rust_circuit(std::shared_ptr<rust_circuit>(result.circuit, qk_circuit_free));
+  transpiled.set_target(target);
 
   qk_transpile_layout_free(result.layout);
+  target.reset();
 
   return transpiled;
 }

src/primitives/containers/bit_array.hpp

@@ -136,7 +136,7 @@ std::unordered_map<std::string, uint_t> BitArray::get_counts(void)
 {
     std::unordered_map<std::string, uint_t> ret;
     for (int_t i = 0; i < array_.size(); i++) {
-        ret[array_[i].to_hex_string()]++;
+        ret[array_[i].to_string()]++;
     }
     return ret;
 }

src/providers/backend.hpp

@@ -61,7 +61,7 @@ class BackendV2 {
 
     /// @brief Return a target properties for this backend
     /// @return a target class
-    virtual transpiler::Target target(void) = 0;
+    virtual std::shared_ptr<transpiler::Target> target(void) = 0;
 
     /// @brief Run and collect samples from each pub.
     /// @param pubs An iterable of pub-like objects.

src/providers/qrmi_backend.hpp

@@ -44,6 +44,7 @@ class QRMIBackend : public BackendV2 {
     std::string primitive_name_ = "sampler";
     std::string acc_token_;
     std::shared_ptr<QrmiQuantumResource> qrmi_ = nullptr;
+    std::shared_ptr<transpiler::Target> target_ = nullptr;
 public:
     /// @brief Create a new QRMIBackend
     QRMIBackend() {}
@@ -66,18 +67,23 @@ class QRMIBackend : public BackendV2 {
 
     /// @brief Return a target properties for this backend
     /// @return a target class
-    transpiler::Target target(void) override
+    std::shared_ptr<transpiler::Target> target(void) override
     {
+        if (target_) {
+            return target_;
+        }
         transpiler::Target target;
 
         char *target_str = NULL;
         QrmiReturnCode rc = qrmi_resource_target(qrmi_.get(), &target_str);
-        if (rc == QRMI_RETURN_CODE_SUCCESS) {
-            nlohmann::ordered_json json_target = nlohmann::ordered_json::parse(target_str);
-            qrmi_string_free((char *)target_str);
-            target.from_json(json_target);
+        if (rc != QRMI_RETURN_CODE_SUCCESS) {
+            return nullptr;
         }
-        return target;
+        nlohmann::ordered_json json_target = nlohmann::ordered_json::parse(target_str);
+        qrmi_string_free((char *)target_str);
+        target_ = std::make_shared<transpiler::Target>();
+        target_->from_json(json_target);
+        return target_;
     }
 
     /// @brief Run and collect samples from each pub.
@@ -186,6 +192,7 @@ class QRMIBackend : public BackendV2 {
         qrmi_resource_task_stop(qrmi_.get(), job_id.c_str());
         return ret;
     }
+
 };
 
 } // namespace providers

src/transpiler/target.hpp

@@ -51,7 +51,7 @@ class Target {
       qk_target_free(target_);
     }
   }
-  const bool is_set(void) const
+  bool is_set(void) const
   {
     return is_set_;
   }
@@ -67,6 +67,13 @@ class Target {
     return backend_name_;
   }
 
+  /// @brief number of qubits
+  /// @return number of qubits
+  uint_t num_qubits(void) const
+  {
+    return num_qubits_;
+  }
+
   /// @brief basis gates for this target
   /// @return a list of basis gates in string
   const std::vector<std::string>& basis_gates(void) const
@@ -116,6 +123,11 @@ bool Target::from_json(nlohmann::ordered_json& input)
   std::unordered_map<std::string, QkTargetEntry*> property_map;
   for (auto& prop : backend_properties["gates"]) {
     std::string gate = prop["gate"];
+    if (gate == "rzz") {
+      // TODO: Add RZZ support when we have angle wrapping in
+      // Qiskit's target and C transpiler.
+      continue;
+    }
     std::vector<uint32_t> qubits = prop["qubits"];
     double duration = 0.0;
     double error = 0.0;

src/utils/bitvector.hpp

@@ -170,7 +170,7 @@ void BitVector::from_hex_string(const std::string &src, const uint_t base) {
   }
   allocate(size*4, base);
 
-  for (int_t i = 0; i < src.size(); i++) {
+  for (int_t i = 0; i < size; i++) {
     char c = src[src.size() - 1 - i];
     uint_t h = 0;
     if (c >= '0' && c <= '9') {
@@ -180,8 +180,8 @@ void BitVector::from_hex_string(const std::string &src, const uint_t base) {
     } else if(c >= 'A' && c <= 'F') {
       h = (uint_t)(c - 'A') + 10;
     }
-    uint_t pos = i % (REG_SIZE >> 4);
-    bits_[i / (REG_SIZE >> 4)] |= (h << (pos << 4));
+    uint_t pos = i % (REG_SIZE >> 2);
+    bits_[i / (REG_SIZE >> 2)] |= (h << (pos << 2));
   }
 }
 
@@ -229,14 +229,19 @@ std::string BitVector::to_string(void) {
 }
 
 std::string BitVector::to_hex_string(void) {
+  uint_t size = size_/4;
   std::string str = "0x";
-  for (uint_t i = 0; i < size_/4; i++) {
-    uint_t pos = i % (REG_SIZE >> 4);
-    uint_t val = (bits_[(size_/4 - 1 - i) / (REG_SIZE >> 4)] >> (pos << 4)) & 0xf;
+  for (uint_t i = 0; i < size; i++) {
+    str += '0';
+  }
+  for (uint_t i = 0; i < size; i++) {
+    uint_t pos = i % (REG_SIZE >> 2);
+    uint_t val = (bits_[i / (REG_SIZE >> 2)] >> (pos << 2)) & 15;
+
     if (val < 10) {
-      str += ('0' + val);
+      str[str.size() - 1 - i] = ('0' + val);
     } else {
-      str += ('a' + (val - 10));
+      str[str.size() - 1 - i] = ('a' + (val - 10));
     }
   }
   return str;

tests/transpile_test.cpp

@@ -44,6 +44,7 @@ int main()
   for (int i=0;i<9;i++) {
     circ.cx(i, i+1);
   }
+  circ.rzz(0.1, 0, 1);
   for (int i=0;i<10;i++) {
     circ.measure(i,i);
   }