NOW CURRENTLY I AM IN 12TH STD(SCIENCE),I WANT TO BECOME A QUANTUM PHYSICIST,SO WHAT SHOULD I TAKE(ENGINEERING OR MEDICAL). AFTER 12TH BOARD EXAMS,HOW MUCH YEARS IT WOULD TAKE TO COMPLETE MY Ph.D. DEGREE.WHICH COMPETITIVE ENTRANCE EXAM SHOULD I GIVE(e.g. JEE,NEET, MH-CET,ISEET,ETC) AFTER COMPLETING 12TH STD ?

@ xavier 
You need to give engg as ur choice to become as a quantum physicist , 
and choose iit or bits as your dream destination , and attempt both JEE and bitsat for that , 
in bits also , u will get enough opputunity , 

after doing 4 years in engg physics branch , u can write GATE exam and could enter MIT also if scored good rank , then go for p.hd from a recognised university , u will take 5 years there . 
and then u can be a quantum physicist , and REMEMBER , RESEARCH IN PHY IS NOT THAT MUCH EASY , AND U NEED TO DO HARD WORK FOR THAT 
ALL THE BEST ..