How to make API invocations async in tornado

I have started my web server using the below statement

tornado.ioloop.IOLoop.current().start()

I have marked my methods with @gen.coroutine and return as yield In order to check if the method calls are async, i added time.sleep(5) but the method calls are all synchronous it waits for 5 sec and the executes the next statements, any other call to the tornado server just waits for the first call to complete. How to make my APIS async

I don't have any IO calls in my methods, but CPU intensive mathematical calculations.