Fixed IonQ backend implementation:

- Batch mode: override base RemoteAccelerator to run one-by-one.

- Fixed U3 decompose for IonQProgramVisitor: looks like the decomposition is not correct (incorrect results). Also, IonQ supports native sqrt-X gate, hence just use the same U3 -> (sx-rz) as that of IBM.

Tested by: running on IonQ remote simulator.
Signed-off-by: Thien Nguyen <nguyentm@ornl.gov>

quantum/plugins/ionq/ionq_accelerator.cpp

@@ -50,6 +50,20 @@ void IonQAccelerator::initialize(const HeterogeneousMap &params) {
   }
 }
 
+// Note: IonQ don't support batching. 
+void IonQAccelerator::execute(
+    std::shared_ptr<AcceleratorBuffer> buffer,
+    const std::vector<std::shared_ptr<CompositeInstruction>> circuits) {
+  for (const auto &f : circuits) {
+    auto tmpBuffer =
+        std::make_shared<xacc::AcceleratorBuffer>(f->name(), buffer->size());
+    // Run each circuit
+    RemoteAccelerator::execute(tmpBuffer, f);
+    // tmpBuffer->print();
+    buffer->appendChild(f->name(), tmpBuffer);
+  }
+}
+
 const std::string IonQAccelerator::processInput(
     std::shared_ptr<AcceleratorBuffer> buffer,
     std::vector<std::shared_ptr<CompositeInstruction>> functions) {
@@ -80,7 +94,7 @@ const std::string IonQAccelerator::processInput(
   using json = nlohmann::json;
   json jj;
   to_json(jj, prog);
-
+  xacc::info("IonQ Job JSON:\n" + jj.dump(4) + "\n");
   return jj.dump();
 }
 
@@ -145,6 +159,8 @@ void IonQAccelerator::processResponse(std::shared_ptr<AcceleratorBuffer> buffer,
     buffer->appendMeasurement(getBitStrForInt(std::stoi(kv.first)),
                               std::ceil(kv.second * shots));
   }
+
+  xacc::info("IonQ Result JSON:\n" + j.dump(4) + "\n");
   return;
 }
 

quantum/plugins/ionq/ionq_accelerator.hpp

@@ -24,7 +24,9 @@ namespace quantum {
 class IonQAccelerator : public RemoteAccelerator {
 public:
   void cancel() override;
-
+  void execute(std::shared_ptr<AcceleratorBuffer> buffer,
+               const std::vector<std::shared_ptr<CompositeInstruction>>
+                   circuits) override;
   void initialize(const HeterogeneousMap &params = {}) override;
   void updateConfiguration(const HeterogeneousMap &config) override {
     if (config.keyExists<int>("shots")) {

quantum/plugins/ionq/ionq_program_visitor.hpp

@@ -151,16 +151,49 @@ public:
   }
 
   void visit(U &u) override {
-    auto t = u.getParameter(0).toString();
-    auto p = u.getParameter(1).toString();
-    auto l = u.getParameter(2).toString();
-
-    Rz rz(u.bits()[0], t);
-    Ry ry(u.bits()[0], p);
-    Rz rz2(u.bits()[0], l);
-    visit(rz);
-    visit(ry);
-    visit(rz2);
+    auto t = u.getParameter(0).as<double>();
+    auto p = u.getParameter(1).as<double>();
+    auto l = u.getParameter(2).as<double>();
+    auto qubit = u.bits()[0];
+    {
+      // u3_qasm_def.rz(lam, 0)
+      xacc::ionq::CircuitInstruction inst;
+      inst.set_gate("rz");
+      inst.set_target(qubit);
+      inst.set_rotation(l);
+      instructions.push_back(inst);
+    }
+    {
+      // u3_qasm_def.sx(0)
+      // v = Square root of not gate
+      xacc::ionq::CircuitInstruction inst;
+      inst.set_gate("v");
+      inst.set_target(qubit);
+      instructions.push_back(inst);
+    }
+    {
+      // u3_qasm_def.rz(theta+pi, 0)
+      xacc::ionq::CircuitInstruction inst;
+      inst.set_gate("rz");
+      inst.set_target(qubit);
+      inst.set_rotation(t + M_PI);
+      instructions.push_back(inst);
+    }
+    {
+      // u3_qasm_def.sx(0)
+      xacc::ionq::CircuitInstruction inst;
+      inst.set_gate("v");
+      inst.set_target(qubit);
+      instructions.push_back(inst);
+    }
+    {
+      // u3_qasm_def.rz(phi+3*pi, 0)
+      xacc::ionq::CircuitInstruction inst;
+      inst.set_gate("rz");
+      inst.set_target(qubit);
+      inst.set_rotation(p + 3.0 * M_PI);
+      instructions.push_back(inst);
+    }
   }
 
   void visit(Rx &rx) override {