Add enumerated noise_model_type to noise interface (#2200)

docs/sphinx/api/languages/cpp_api.rst

@@ -115,6 +115,8 @@ Noise Modeling
 .. doxygenclass:: cudaq::noise_model
     :members:
 
+.. doxygenenum:: cudaq::noise_model_type
+
 Kernel Builder
 ===============
 

runtime/common/NoiseModel.cpp

@@ -82,7 +82,9 @@ kraus_channel::kraus_channel(std::vector<kraus_op> &_ops) : ops(_ops) {
   validateCompleteness();
 }
 
-kraus_channel::kraus_channel(const kraus_channel &other) : ops(other.ops) {}
+kraus_channel::kraus_channel(const kraus_channel &other)
+    : ops(other.ops), noise_type(other.noise_type),
+      parameters(other.parameters) {}
 
 std::size_t kraus_channel::size() const { return ops.size(); }
 
@@ -94,6 +96,8 @@ kraus_op &kraus_channel::operator[](const std::size_t idx) { return ops[idx]; }
 
 kraus_channel &kraus_channel::operator=(const kraus_channel &other) {
   ops = other.ops;
+  noise_type = other.noise_type;
+  parameters = other.parameters;
   return *this;
 }
 

runtime/common/NoiseModel.h

@@ -19,6 +19,17 @@
 
 namespace cudaq {
 
+/// @brief Noise model enumerated type that allows downstream simulators of
+/// `kraus_channel` objects to apply simulator-specific logic for well-known
+/// noise models.
+enum class noise_model_type {
+  unknown,
+  depolarization_channel,
+  amplitude_damping_channel,
+  bit_flip_channel,
+  phase_flip_channel
+};
+
 /// @brief A kraus_op represents a single Kraus operation,
 /// described as a complex matrix of specific size. The matrix
 /// is represented here as a 1d array (specifically a std::vector).
@@ -107,6 +118,12 @@ class kraus_channel {
   }
 
 public:
+  /// @brief Noise type enumeration
+  noise_model_type noise_type = noise_model_type::unknown;
+
+  /// @brief Noise parameter values
+  std::vector<real> parameters;
+
   ~kraus_channel() = default;
 
   /// @brief The nullary constructor
@@ -340,6 +357,8 @@ class depolarization_channel : public kraus_channel {
         k3v{std::sqrt(probability / three), 0, 0,
             negOne * std::sqrt(probability / three)};
     ops = {k0v, k1v, k2v, k3v};
+    this->parameters.push_back(probability);
+    noise_type = noise_model_type::depolarization_channel;
     validateCompleteness();
   }
 };
@@ -353,6 +372,8 @@ class amplitude_damping_channel : public kraus_channel {
     std::vector<cudaq::complex> k0v{1, 0, 0, std::sqrt(1 - probability)},
         k1v{0, std::sqrt(probability), 0, 0};
     ops = {k0v, k1v};
+    this->parameters.push_back(probability);
+    noise_type = noise_model_type::amplitude_damping_channel;
     validateCompleteness();
   }
 };
@@ -367,6 +388,8 @@ class bit_flip_channel : public kraus_channel {
                                     std::sqrt(1 - probability)},
         k1v{0, std::sqrt(probability), std::sqrt(probability), 0};
     ops = {k0v, k1v};
+    this->parameters.push_back(probability);
+    noise_type = noise_model_type::bit_flip_channel;
     validateCompleteness();
   }
 };
@@ -382,6 +405,8 @@ class phase_flip_channel : public kraus_channel {
                                     std::sqrt(1 - probability)},
         k1v{std::sqrt(probability), 0, 0, negOne * std::sqrt(probability)};
     ops = {k0v, k1v};
+    this->parameters.push_back(probability);
+    noise_type = noise_model_type::phase_flip_channel;
     validateCompleteness();
   }
 };