What field should I choose if I want to do quantum information in future but there isn't a group in my university?
I am going to give you the same (very good) advice that I received when I asked a similar question a few months ago: don't ask us, ask them. 


Find the names of some quantum information theorists.
Send a brief and polite email expressing interest in their research.
Ask them what kind of things you should specialise in, or what type
of courses you should take to help you reach your goal.
Don't be surprised if you don't get too many responses; academics are busy people. 
Keep trying. If that's the area of research you really want to pursue, go for it. Read some journal articles. Find a good textbook and get stuck in.


Finally (and this is an important one), as Martin said in his answer to my question: 


  "Quite a lot of people in senior levels in cosmology are interested in
  cosmology and are glad to find interest in cosmology in other people."


and this applies to quantum information too.