Minor fix in quantum_neural_net.py (#1328)

**Title:**
Minor fix in quantum_neural_net.py
**Summary:**
qml.quadX is not supported in pennylane≤0.29 and results in error.
Change to qml.X
**Relevant references:**

**Possible Drawbacks:**

**Related GitHub Issues:**

Author: ghlrobin

demonstrations/quantum_neural_net.metadata.json

@@ -6,7 +6,7 @@
         }
     ],
     "dateOfPublication": "2019-10-11T00:00:00+00:00",
-    "dateOfLastModification": "2024-10-07T00:00:00+00:00",
+    "dateOfLastModification": "2025-03-20T00:00:00+00:00",
     "categories": [
         "Quantum Machine Learning"
     ],

demonstrations/quantum_neural_net.py

@@ -17,7 +17,7 @@
    pytorch_noise PyTorch and noisy devices
    tutorial_noisy_circuit_optimization Optimizing noisy circuits with Cirq
 
-*Author: Maria Schuld — Posted: 11 October 2019. Last updated: 25 January 2021.*
+*Author: Maria Schuld — Posted: 11 October 2019. Last updated: 20 March 2025.*
 
 .. warning::
     This demo is only compatible with PennyLane version ``0.29`` or below.
@@ -84,7 +84,7 @@ def quantum_neural_net(var, x):
     for v in var:
         layer(v)
 
-    return qml.expval(qml.QuadX(0))
+    return qml.expval(qml.X(0))
 
 
 ##############################################################################
@@ -741,4 +741,4 @@ def cost(var, features, labels):
 ##############################################################################
 # About the author
 # ----------------
-#
+#