Remove references from notebooks

Author: dstrain115

docs/simulate/noisy_simulation.ipynb

@@ -476,7 +476,9 @@
    "outputs": [],
    "source": [
     "\"\"\"Minimal example of defining a custom channel.\"\"\"\n",
-    "class BitAndPhaseFlipChannel(cirq.SingleQubitGate):\n",
+    "class BitAndPhaseFlipChannel(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def __init__(self, p: float) -> None:\n",
     "        self._p = p\n",
     "    \n",

docs/start/intro.ipynb

@@ -1525,7 +1525,7 @@
     "\\end{array} \\right]\n",
     "$$\n",
     "\n",
-    "Below is a simple implementation of this gate in Cirq.  To do this we simply define a class that inherits from `cirq.SingleQubitGate` and implements the `cirq.SupportsUnitary` protocol by implementing the `_unitary_(self)` method.  We also define an optional `__str__` representation which Cirq will use when printing this gate out in a circuit diagram."
+    "Below is a simple implementation of this gate in Cirq.  To do this we simply define a class that inherits from `cirq.Gate` and implements the `cirq.SupportsUnitary` protocol by implementing the `_unitary_(self)` method.  We also define an optional `__str__` representation which Cirq will use when printing this gate out in a circuit diagram."
    ]
   },
   {
@@ -1539,7 +1539,9 @@
     "\"\"\"Example of defining a custom gate in Cirq.\"\"\"\n",
     "\n",
     "\n",
-    "class RationalGate(cirq.SingleQubitGate):\n",
+    "class RationalGate(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def _unitary_(self):\n",
     "        return np.array([[3 / 5, 4 / 5], [-4 / 5, 3 / 5]])\n",
     "\n",
@@ -1780,7 +1782,9 @@
     "\"\"\"Example of a custom gate which supports the decompose protocol.\"\"\"\n",
     "\n",
     "\n",
-    "class HXGate(cirq.SingleQubitGate):\n",
+    "class HXGate(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def _decompose_(self, qubits):\n",
     "        return cirq.H(*qubits), cirq.X(*qubits)\n",
     "\n",
@@ -2832,7 +2836,9 @@
    },
    "outputs": [],
    "source": [
-    "class InconsistentXGate(cirq.SingleQubitGate):\n",
+    "class InconsistentXGate(cirq.Gate):\n",
+    "    def _num_qubits_(self) -> int:\n",
+    "        return 1\n",
     "    def _decompose_(self, qubits):\n",
     "        yield cirq.H(qubits[0])\n",
     "        yield cirq.Z(qubits[0])\n",