Clearly separated CUDA-Q backend execution from CPU Demo fallback

qlbm_embedded.py

@@ -167,8 +167,8 @@ def init_state():
         
         # Backend
         "qlbm_backend_type": None,
-        "qlbm_selected_simulator": "IBM Qiskit simulator",
-        "qlbm_selected_qpu": "IBM QPU",
+        "qlbm_selected_simulator": None,
+        "qlbm_selected_qpu": None,
         
         # Simulation state
         "qlbm_is_running": False,
@@ -1050,8 +1050,8 @@ def run_simulation():
             _state.qlbm_status_message = "Simulation completed successfully."
             _state.qlbm_status_type = "success"
         
-        # === CUDA-Q or CPU Demo Backend ===
-        else:
+        # === CUDA-Q Backend ===
+        elif _state.qlbm_backend_type == "Simulator" and _state.qlbm_selected_simulator == "CUDA-Q simulator":
             _state.qlbm_qiskit_mode = False  # Use PyVista display
             
             grid_size = int(_state.qlbm_grid_size)
@@ -1082,7 +1082,8 @@ def run_simulation():
                     progress_callback=_progress_callback
                 )
             else:
-                log_to_console("Running CPU Demo Simulation...")
+                # Fallback to CPU demo if CUDA-Q not available
+                log_to_console("CUDA-Q not available, falling back to CPU Demo...")
                 frames, times, grid_obj = _run_cpu_demo_simulation(
                     grid_size=grid_size,
                     T=T,
@@ -1127,6 +1128,69 @@ def run_simulation():
                 log_to_console("Error: Simulation produced no data.")
                 _state.qlbm_status_message = "Error: No data produced"
                 _state.qlbm_status_type = "error"
+        
+        # === CPU Demo Backend (for QPU or fallback) ===
+        else:
+            _state.qlbm_qiskit_mode = False  # Use PyVista display
+            
+            grid_size = int(_state.qlbm_grid_size)
+            num_reg_qubits = int(math.log2(grid_size)) if grid_size > 0 else 3
+            T = int(_state.qlbm_time_steps)
+            distribution_type = _state.qlbm_dist_type
+            boundary_condition = _state.qlbm_boundary_condition
+            
+            vx_func = make_velocity_func(_state.qlbm_vx_expr)
+            vy_func = make_velocity_func(_state.qlbm_vy_expr)
+            vz_func = make_velocity_func(_state.qlbm_vz_expr)
+            
+            _progress_callback(0)
+            
+            # CPU Demo Simulation
+            log_to_console("Running CPU Demo Simulation...")
+            frames, times, grid_obj = _run_cpu_demo_simulation(
+                grid_size=grid_size,
+                T=T,
+                distribution_type=distribution_type or "Sinusoidal",
+                vx_func=vx_func,
+                vy_func=vy_func,
+                vz_func=vz_func,
+                progress_callback=_progress_callback
+            )
+            
+            _progress_callback(100)
+            
+            # Update plotter with results
+            if grid_obj:
+                _plotter.clear()
+                isosurfaces = grid_obj.contour(isosurfaces=7, scalars="scalars")
+                _plotter.add_mesh(isosurfaces, cmap="Blues", opacity=0.3, show_scalar_bar=True)
+                _plotter.add_axes()
+                _plotter.show_grid()
+            
+            # Store Results
+            if frames and len(frames) > 0:
+                simulation_data_frames = frames
+                simulation_times = times
+                current_grid_object = grid_obj
+                
+                _state.qlbm_max_time_step = len(frames) - 1
+                _state.qlbm_time_val = 0
+                _state.qlbm_time_slider_labels = [f"{t:.1f}" for t in times] if times else [str(i) for i in range(len(frames))]
+                _state.qlbm_simulation_has_run = True
+                
+                _ensure_point_picking(on_pick_point)
+                
+                if hasattr(_ctrl, "qlbm_view_update"):
+                    _ctrl.qlbm_view_update()
+                log_to_console("Simulation completed successfully.")
+                _state.qlbm_status_message = "Simulation completed successfully."
+                _state.qlbm_status_type = "success"
+                _state.qlbm_simulation_progress = 100
+            else:
+                _state.qlbm_run_error = "Simulation produced no data."
+                log_to_console("Error: Simulation produced no data.")
+                _state.qlbm_status_message = "Error: No data produced"
+                _state.qlbm_status_type = "error"
 
     except Exception as e:
         _state.qlbm_run_error = f"Simulation failed: {str(e)}"
@@ -1485,9 +1549,9 @@ def _build_control_panels(plotter):
                         density="compact",
                         children=[
                             "Selected: ",
-                            "{{ qlbm_backend_type || '—' }}",
+                            "{{ qlbm_backend_type || 'None - Please select a backend' }}",
                             " - ",
-                            "{{ qlbm_backend_type === 'Simulator' ? qlbm_selected_simulator : (qlbm_backend_type === 'QPU' ? qlbm_selected_qpu : '—') }}",
+                            "{{ qlbm_backend_type === 'Simulator' ? (qlbm_selected_simulator || '—') : (qlbm_backend_type === 'QPU' ? (qlbm_selected_qpu || '—') : '—') }}",
                         ],
                     )
             with vuetify3.VMenu(open_on_hover=True, close_on_content_click=True, location="end"):
@@ -1498,6 +1562,7 @@ def _build_control_panels(plotter):
                         with vuetify3.Template(v_slot_activator="{ props }"):
                             vuetify3.VListItem(v_bind="props", title="Simulator", prepend_icon="mdi-robot-outline", append_icon="mdi-chevron-right")
                         with vuetify3.VList(density="compact"):
+                            vuetify3.VListItem(title="CUDA-Q simulator", click="qlbm_backend_type = 'Simulator'; qlbm_selected_simulator = 'CUDA-Q simulator'")
                             vuetify3.VListItem(title="IBM Qiskit simulator", click="qlbm_backend_type = 'Simulator'; qlbm_selected_simulator = 'IBM Qiskit simulator'")
                     with vuetify3.VMenu(open_on_hover=True, close_on_content_click=True, location="end", offset=8):
                         with vuetify3.Template(v_slot_activator="{ props }"):
@@ -1521,7 +1586,7 @@ def _build_control_panels(plotter):
                 text="Run",
                 color="primary",
                 block=True,
-                disabled=("qlbm_is_running || !qlbm_simulation_backend_ready", False),
+                disabled=("qlbm_is_running || !qlbm_backend_type", True),
                 click=run_simulation,
                 style=("qlbm_is_running ? '' : 'background-color:#87CEFA;'", ""),
             )