What are options for a mechanical engineering student in pure physics?

I am a student of mechanical engineering in IIT Rooekee, India.I am more interested in pure Physics.I want to know what are scopes for me in pure Physics after my BTech.I mean what will be procedures for admission in MS or PhD from institutions like MIT or CalTech...I also want to know if any interns or something i can get in area of pure physics during my BTech years if i keep in touch of knowledge of physics.