IIT Kanpur is a better choice if you want to opt for theoretical physics (especially quantum mechanics) than IISC Bangalore.
IISC Bangalore is better for Theoretical Physics. If you want a career in research, this is the best option. At IISC, you will get the opportunity to learn from reputed scientists and work under them. During your course, you will do cool summer projects.
The research experience, exceptional learning opportunities, and IISc tag can help a lot to build a career in research.
Quantum mechanics is as exciting as it sounds. TIFR Mumbai or ICTS Bangalore will be great options. These institutes provide the fundamental outlooks of the course.
For undergraduate, you can go to IIT Kanpur or IIT Madras. But if you want to pursue further studies go to the institutes recommended above.
And if you are choosing Quantum Mechanics as your field of study, then opting for TIFR, located both in Mumbai and Bangalore, should be your primary priority. According to student reviews, TIFR (Mumbai or Bangalore) is better than IISc Bangalore.
TIFR is widely renowned to be the best for the department of Theoretical physics in India. IITK and IISc are known famously to concentrate, for the most part, on Engineering.