Ajax with Joomla

jQuery.ajax({
 type: "POST",
 url: "/index.php",
 data: "tmpl=ajax",//in templates/system/ I create a file called ajax, which is a view.  All my php goes there
 success: function(response){
  alert(response);
 },
 error: function(er){
 alert("error! "+er);
 return false;
 }
 });