Added conditional_if/while examples

Signed-off-by: Vlad Gheorghiu <[email protected]>

CHANGES.md

@@ -22,6 +22,18 @@
 - Added
   [["examples/circuits/post_selection.cpp"](https://github.com/softwareQinc/qpp/blob/main/examples/circuits/post_selection.cpp)]
   example
+- New feature: implemented support for conditional statements in
+  ["qpp/classes/qcircuit.hpp"]
+- Implemented `qpp::QCircuit::`
+  - `QCircuit& cond_if()` - conditional IF statement
+  - `QCircuit& cond_else()` - conditional ELSE statement
+  - `QCircuit& cond_while()` - conditional WHILE statement
+  - `QCircuit& cond_end()` - conditional END block delimiter
+- Added
+  [["examples/circuits/conditional_if.cpp"](https://github.com/softwareQinc/qpp/blob/main/examples/circuits/conditional_if.cpp)]
+  and
+  [["examples/circuits/conditional_while.cpp"](https://github.com/softwareQinc/qpp/blob/main/examples/circuits/conditional_while.cpp)]
+  examples
 - Refactored `qpp::QCircuit::GateStep/MeasurementStep/NOPStep` into separate
   files ["qpp/internal/classes/qcircuit_gate_step.hpp"],
   ["qpp/internal/classes/qcircuit_measurement_step.hpp"], and
@@ -49,9 +61,9 @@
 - Simplified MATLAB detection via CMake `find_package()` function. Users should
   only use `-DQPP_MATLAB=ON` when building with MATLAB support, all other
   MATLAB-related CMake flags have been removed.
-- Bugfix in qpp::adjoint(QCircuit);
-- Introduced conditional statements
-- cond_func_t type alias
+- Bugfix in `qpp::adjoint(QCircuit)`
+- Added `cond_func_t` type alias in ["qpp/types.hpp"] for boolean predicates of
+  the form `std::vector<idx> -> bool`
 
 # Version 5.1 - 1 March 2024
 

examples/circuits/conditional_if.cpp

@@ -0,0 +1,59 @@
+// Conditional IF quantum circuit simulator
+// Source: ./examples/circuits/conditional_if.cpp
+
+#include <iostream>
+
+#include "qpp/qpp.hpp"
+
+int main() {
+    using namespace qpp;
+
+    std::cout << ">> Conditional IF quantum circuit simulator\n\n";
+
+    // quantum circuit with 2 qubits and 2 classical bits
+    QCircuit qc{3, 3};
+    // prepare the first qubit in the |+> state
+    qc.gate(gt.H, 0);
+    // measure the first qubit non-destructively
+    qc.measure(0, 0, false);
+
+    // define a boolean predicate of the required form std::vector<idx> -> bool
+    auto pred = [](std::vector<idx> dits) {
+        // returns true when the first dit is 1 at runtime (when run by a
+        // quantum engine); in our case, this corresponds to the result of the
+        // measurement result of the first qubit
+        return dits[0] == 1;
+    };
+    // conditional IF statement
+    // flips the second qubit when the predicate above was true, otherwise
+    // flips the third qubit
+    qc.cond_if(pred);
+    // curly braces are optional, used to force code indenting
+    {
+        qc.gate(gt.X, 1); // the final state will be |110>
+    }
+    qc.cond_else();
+    {
+        qc.gate(gt.X, 2); // the final state will be |001>
+    }
+    qc.cond_end();
+
+    // measure the second and third qubits non-destructively
+    qc.measure(1, 1, false);
+    qc.measure(2, 2, false);
+
+    // display the quantum circuit and its corresponding resources
+    std::cout << qc << "\n\n" << qc.get_resources() << "\n\n";
+
+    // initialize the quantum engine with the circuit
+    QEngine engine{qc};
+
+    // execute the entire circuit once
+    engine.execute();
+
+    // display the measurement statistics
+    std::cout << engine << "\n\n";
+    // display the output quantum state
+    std::cout << ">> Final state:\n";
+    std::cout << disp(dirac(engine.get_state())) << '\n';
+}

examples/circuits/conditional_while.cpp

@@ -0,0 +1,52 @@
+// Conditional WHILE quantum circuit simulator
+// Source: ./examples/circuits/conditional_while.cpp
+
+#include <iostream>
+
+#include "qpp/qpp.hpp"
+
+int main() {
+    using namespace qpp;
+
+    std::cout << ">> Conditional WHILE quantum circuit simulator\n\n";
+
+    // quantum circuit with 2 qubits and 2 classical bits
+    QCircuit qc{3, 3};
+
+    // define a boolean predicate of the required form std::vector<idx> -> bool
+    auto pred = [](std::vector<idx> dits) {
+        // returns true as long as the first two classical dits ARE NOT 1, 1
+        return !(dits[0] == 1 && dits[1] == 1);
+    };
+
+    // conditional WHILE statement
+    // keep preparing the first measuring the first 2 qubits non-destructively
+    // until we obtain the result 1, 1
+    qc.cond_while(pred);
+    // curly braces are optional, used to force code indenting
+    {
+        qc.reset({0, 1}); // resets the first two qubits to the |00> state
+        qc.gate_fan(gt.H, {0, 1});    // next, prepare them in the |++> state
+        qc.measure({0, 1}, 0, false); // finally, measure them non-destructively
+    } // keep repeating until both measurement results are 1, 1
+    qc.cond_end();
+
+    // the WHILE statement finished, flip the state of the third qubit
+    qc.gate(gt.X, 2); // the final state will be |111>
+    qc.measure(2, 2); // measure the third qubit non-destructively
+
+    // display the quantum circuit and its corresponding resources
+    std::cout << qc << "\n\n" << qc.get_resources() << "\n\n";
+
+    // initialize the quantum engine with the circuit
+    QEngine engine{qc};
+
+    // execute the entire circuit once
+    engine.execute();
+
+    // display the measurement statistics
+    std::cout << engine << "\n\n";
+    // display the output quantum state
+    std::cout << ">> Final state:\n";
+    std::cout << disp(dirac(engine.get_state())) << '\n';
+}

examples/circuits/noisy_teleport_qubit_circuit.cpp

@@ -1,4 +1,4 @@
-// Qubit noisy teleportation circuit simulator
+// Qubit noisy teleportation quantum circuit simulator
 // Source: ./examples/circuits/noisy_teleport_qubit_circuit.cpp
 
 #include <iostream>

examples/circuits/post_selection.cpp

@@ -1,4 +1,4 @@
-// Qubit post-selection circuit simulator
+// Qubit post-selection quantum circuit simulator
 // Source: ./examples/circuits/post_selection.cpp
 
 #include <iostream>

examples/circuits/qpe_circuit.cpp

@@ -1,4 +1,4 @@
-// Quantum phase estimation circuit simulator
+// Quantum phase estimation quantum circuit simulator
 // Source: ./examples/circuits/qpe_circuit.cpp
 // See also ./examples/qpe.cpp for a low-level API example
 

examples/circuits/teleport_qubit_circuit.cpp

@@ -1,4 +1,4 @@
-// Qubit teleportation circuit simulator
+// Qubit teleportation quantum circuit simulator
 // Source: ./examples/circuits/teleport_qubit_circuit.cpp
 
 #include <iostream>

examples/circuits/teleport_qudit_circuit.cpp

@@ -1,4 +1,4 @@
-// Qudit teleportation circuit simulator
+// Qudit teleportation quantum circuit simulator
 // Source: ./examples/circuits/teleport_qudit_circuit.cpp
 
 #include <iostream>

include/qpp/types.hpp

@@ -222,7 +222,6 @@ struct dirac_t {
  * \brief Conditional functor type in qpp::QCircuit conditional statements
  */
 using cond_func_t = std::function<bool(std::vector<idx>)>;
-// using cond_func_t = bool (*)(std::vector<idx>);
 
 /**
  * \brief Quantumly-accessible Random Access Memory (qRAM)