Merge remote-tracking branch 'upstream/master' into tnguyen/py-qcor-observe-retrieve-term-data

// Compile to run with validation mode: 

// Qpp (noiseless)

// qcor -validate deuteron_validation.cpp -shots 1024

// Aer (noisy)

// qcor -validate deuteron_validation.cpp -shots 1024 -qpu aer[noise-model:noise_model.json]

__qpu__ void deuteron(qreg q, double theta) {

  X(q[0]);

  Ry(q[1], theta);

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

  // for (int i = 0; i < 20; i++) {

  //   CNOT(q[1], q[0]);

  // }

  H(q[0]);

  H(q[1]);

  Measure(q[0]);

  Measure(q[1]);

}

int main() {

  qcor::set_verbose(true);

  const double angle = 0.297113;

  auto q = qalloc(2);

  deuteron(q, angle);

  q.print();

  std::cout << "<XX> = " << q.exp_val_z() << "\n";

}

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