Use Dual() to give each quarter its underlying date or numeric value. If you aren't tied to this specific format, Qlik has a built-in Quartername() function as well, but it won't match the format you're currently using.

From this specific format, you could probably do something like num(Right(Quarter,2) & left(Quarter,1)) for the numeric part of the dual(), but if you have the underlying date you could just use that.