fixed formulas for purity RB

Author: ShellyGarion

ignis/RB_advanced.ipynb

@@ -474,7 +474,9 @@
     "\n",
     "To calculate all $Z$ correlators we only need the on diagonal elements of $\\rho$ (i.e. what is measured in experiment). If we apply a $\\pi/2$ rotation to the density matrix and then measure the $Z$ correlator,\n",
     "$$\n",
-    "\\rho^{'}  =  e^{i P_j \\pi/4} \\rho e^{-i P_j \\pi/4} \\\\\n",
+    "\\rho^{'}  =  e^{i P_j \\pi/4} \\rho e^{-i P_j \\pi/4} \n",
+    "$$\n",
+    "$$\n",
     "Tr(Z \\rho^{'})  =  Tr(Z e^{i P_j \\pi/4} \\rho e^{-i P_j \\pi/4}) \n",
     " =  Tr(e^{-i P_j \\pi/4}Z e^{i P_j \\pi/4} \\rho)\n",
     "$$\n",