Update ModelNoise.ipynb

jupyter_notebooks/Tutorials/objects/ModelNoise.ipynb

@@ -212,7 +212,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "#### Nonlocal noise\n",
+    "### Nonlocal noise (crosstalk)\n",
     "So far, all the noise we've specified has been directed at the *target* qubits of the relevant operation.  For instance, when a depolarization strength is specified for a 1-qubit gates, it applies the given depolarization to gate's single target qubit.  When depolarization is applied to a 2-qubit gate, 2-qubit depolarization is applied to the target qubits.  When Lindblad error rates are given for a 1-qubit gate, they are indexed by single Pauli elements, e.g. `('H','X')`, whereas for a 2-qubit gate they are indexed by 2-qubit Paulis, e.g. `('H','XX')`.\n",
     "\n",
     "In a crosstalk-free model, noise can *only* be specified on the target qubits - noise on non-target qubits is simply not allowed.  But for an explicit model, which holds solely $N$-qubit layer operations, noise for a gate (layer) can be applied to *any* of the qubits.  To specify noise that is not on the target qubits of a gate,\n",