adding deuteron H2 expgen example

Signed-off-by: Alex McCaskey <mccaskeyaj@ornl.gov>

examples/deuteron_expgen.cpp

+#include "qcor.hpp"
+
+int main(int argc, char **argv) {
+
+  qcor::Initialize(argc, argv);
+
+  auto optimizer = qcor::getOptimizer(
+      "nlopt", {{"nlopt-optimizer", "cobyla"}, {"nlopt-maxeval", 20}});
+
+  auto op = qcor::getObservable(
+      "pauli", "5.907 - 2.1433 X0X1 - 2.1433 Y0Y1 + .21829 Z0 - 6.125 Z1");
+
+  auto future = qcor::submit([&](qcor::qpu_handler &qh) {
+    qh.vqe(
+        [&](double x) {
+          X(0);
+          exp_i_theta(x, {{"pauli", "X0 Y1 - Y0 X1"}});
+        },
+        op, optimizer);
+  });
+
+  auto results = future.get();
+  auto energy = mpark::get<double>(results->getInformation("opt-val"));
+  std::cout << "Results: " << energy << "\n";
+}

ir/digital/generators/exp/tests/ExpTester.cpp

@@ -12,7 +12,11 @@ TEST(ExpTester, checkSimple) {
   // NOW Test it somehow...
   Exp exp;
   auto f =
-      exp.generate({{"pauli","Y0 X1 X2 X3"}});
+      exp.generate({{"pauli","Y0 X1 X2"}});
+
+      std::cout << "F:\n" << f->toString() << "\n";
+    f =
+      exp.generate({{"pauli","X0 Y1 - X1 Y0"}});
 
       std::cout << "F:\n" << f->toString() << "\n";