From the documentation of QtConcurrent::run:
Note that the QFuture returned by QtConcurrent::run() does not support canceling, pausing, or progress reporting. The QFuture returned can only be used to query for the running/finished status and the return value of the function.
What you could do is have a button press set a boolean flag in your main window and build your infinite loop like this:
_aborted = false;
forever // Qt syntax for "while( 1 )"
{
if( _aborted ) return;
// do your actual work here
}