Course after 12th standard for specific fields

Almost all the branches you are mentioned are specialisations in Physics. So you should have Physics in your Graduation. In addition to Physics, you have to have mathematics also as a subject. You can go to chemistry or any other subject available with the above two subjects in your graduation. After completing your graduation you have to select M.Sc Physics or Applied Physics and in these courses, you can look for the specialisation you prefer. You can select one subject from the list you have mentioned above and you can get a masters degree in that subject. You should have a good hold on physics and once you finish your PG, you can go for your Doctorate degree in the subject of specialisation you choose. Please keep in mind that for all the above subjects Physics is a basic subject and you should have sufficient hold on that physics.
If you choose cosmology, you will be a cosmologist. For that, you can have a master degree in applied physics with specialisation in cosmology. The following institutes are good for cosmology.
1.IISc Bangalore,
2. Andhra University, Visakhapatnam, AP
3, Osmania University, Hyderabad.
4. Punjab University, Patiala.
5. Indian Institute of Science and Technology, Trivandrum
6. Institute of Astrophysics, Bangalore

The above institutes are good for almost all the specialisation you have mentioned.

As you studied PCM in 12th grade and not sure about the forth main subject whether it is Biology or Computer science. For the fields, you mentioned Physics knowledge is very important.
1. Cosmology is the study of the universe. To get into Cosmology, you need to study Physics and Maths in your UG.
2. Nanotechnology involves natural science and again Physics Chemistry and Maths are to be in your UG.
3. Robotics is a good option as you have various degree options in it like Unified Robotics, Robotics Foundation, Robotic Engineering, etc.
You can complete your UG with Physics and Maths as main subjects and then pursue your PG with any one specialization. When you are in UG, you will get an idea based out of the current technology and you can choose your filed accordingly.

Since you are interested to have advanced knowledge in any one of the domains Robotics, Quantum Mechanics, Nanotechnology and Cosmology at the later stage, I would advise you to show your inner passion for both Physics and Mathematics.
To understand the complexities of Physics, you should have conceptual clarities in Mathematics especially in the areas of Calculas, Matrix, Linear Algebra, Complex Number, Vector Algebra, Infinite vector, Trigonometry etc and you would be required to apply these while dealing with the advanced studies of Physics.
The streams discussed above are the extensive studies of Physics in the different domains. In order to clarify these domains, you should be familiar with their definitions. Let us discuss the term one by one -
Cosmology is the detailed study of the branch of Astronomy involving the origin and evolution of the universe. It can be better understood with the application of higher Mathematics.
Nanotechnology relates to the products using tiny materials being used in Electronic devices, Catalysis , Sensors etc
Quantum Physics would deal with extensive studies of Physics in the field of Black Body Radiation, Bohr Model for explaining spectral lines, Stern Gerlach Experiment etc with the application of different branches of Mathematics as discussed above.
However, Robotics is entirely a different branch in the sense that this branch employs the basics of Computer Engineering, Mechanical and Electronic Enginnering.
If you are interested to go in the specialised course relating to Cosmolology or Quantum Mechanics, take up the course of B.Sc with the combination of Physics, Chemistry and Mathematics or still better take up the course of Physics ( Honours) from a reputed university and for post graduation you can seek admission in the following institutions-
1) Tata Institute of Fundamental Research, Mumbai
2) Raman Research Institute, Bengaluru.
3) Indian Institute of Astrophysics,Bengaluru.
4) Physical Research Institute, Ahmedabad.
5) IIT Mumbai
6) IIT Chennai
7) IIT Kanpur etc.
IIT provides five year integrated course for the persuasion of both undergraduate and post graduate level. You will have to qualify the entrance test of IIT to avail this integrated course. During your post graduation stage, you need to take up the specialisation course either in cosmology or in the quantum mechanics.
Other institutes too have their own entrance tests to screen the deserving aspirants.

You have mentioned some of the niche areas of science. Cosmology and Quantum Physics/Mechanics are relatively older ones though a lot of research options are there in them as the field of their investigations is quite big. Nanotechnology and Robotics are modern streams where there is immense scope of research as well as career making in the near future.

It is good that you are having interest and inclination in these advanced areas of present day scientific pursuits and for a science students it makes sense to try in these lines for a robust scientific growth leading to a successful profession. There are some apex institutes in our country like TIFR (Tata Institute of Fundamental Research), IITs (Indian Institute of Technology), IISc (Indian Institute of Science), PRL (Physical Research laboratory), RRI (Raman Research Institute), IIA (Indian Institute of Astrophysics), IIST (India Institutes of Space Science and Technology) etc where one can try to get admission in the relevant courses either graduation or combined graduation and post graduation. These institutions have foreign collaboration also and have research association programs in many advanced countries. Some of these institutes have B.Sc. & M.Sc. integrated programs. Most of them take the students through JEE Advanced but some also have their own tests. For example TIFR takes its own entrance test. Incidentally TIFR has two other institutes under its fold that are ICTS and IISER which are engaged in specific scientific research.

One thing which I want to share with you is that after completing your dream education you might be working in a particular scientific line but the research and higher education in these advanced fields are very much interrelated and many things are commonly applied everywhere. So, at that stage you cannot differentiate between a particular topic with other one as certain basic understandings required would be same in all streams. Essence of this understanding is that we should not ignore or neglect any scientific observation or theory as it could be of immense use at a later stage. When you actively engage in scientific research then you might need inputs and crucial elements from everywhere whether it is Mathematics or Physics or Chemistry. A true scientist has to respect all sort of scientific data from different disciplines. Only then he would be successful in his research projects.

For cosmology and quantum physics most of the above institutes are ideal. For nanotechnology Amity Institute of Nanotechnology, Amrita Centre for Nanosciences, Jawaharlal Nehru Technological University etc are well known. For robotics one can try in Manipal Institute of Technology, Amity University, Osmania University, Guru Gobind Singh Indraprastha University, National Institute of Engineering, Mysore etc.