Added a FTQC extension for Pauli measurement

#include "ftqc/vqe.hpp"

// Compile with:

// qcor -qpu qpp -qrt ftqc -I<qcor/examples/shared> deuteron.cpp 

__qpu__ void ansatz(qreg q, double theta) {

  X(q[0]);

  Ry(q[1], theta);

  CX(q[1], q[0]);

}

__qpu__ void test(qreg q, double theta, std::vector<qcor::PauliOperator> bases) {

  ansatz(q, theta);

  MeasureP(q, bases);

}

int main(int argc, char **argv) {

  // Allocate 2 qubits

  auto q = qalloc(2);

  // auto H = 5.907 - 2.1433 * X(0) * X(1) - 2.1433 * Y(0) * Y(1) + .21829 * Z(0) -

  //          6.125 * Z(1);

  std::vector<qcor::PauliOperator> ops { X(0), X(1)};

  test(q, M_PI_4, ops);

  q.print();

}

#pragma once

#include <vector>

#include "qcor_observable.hpp"

// Measure tensor product of Paulis operators.

// Note: the bases must be elementary (I, X, Y, Z) Pauli ops

__qpu__ void MeasureP(qreg q, std::vector<qcor::PauliOperator> bases) {

  for (int i = 0; i < bases.size(); ++i) {

    auto pauliOp = bases[i];

    const std::string pauliStr = pauliOp.toString().substr(6);

    std::cout << "Pauli: " << pauliStr << "\n";

    const auto bitIdx = std::stoi(pauliStr.substr(1));

    // TODO: fix XASM compiler to handle char literal

    if (pauliStr.rfind("X", 0) == 0) {

      H(q[bitIdx]);

    }

    if (pauliStr.rfind("Y", 0) == 0) {

      Rx(q[bitIdx], M_PI_2);

    }

    std::cout << "Measure q[" << bitIdx << "]\n";

    Measure(q[bitIdx]);

  }

}