JEST

Firstly JEST is to take admission in mostly research oriented Science course if you want to do integrated course of M.Tech Ph.D course, then you can give JEST.
https://www.jest.org.in/eligibility
Here is the eligibility criteria and the institutes you can go for. Also, if you want to do M.Tech then obviously IITs are one of the best option you can check the eligibility and courses offered by IITK https://www.iitk.ac.in/doaa/eligibility-criteria
Also you can check the courses offered by IITB and IITD which have best physics faculty and also ranked in top 200 universities all over the world. I prefer you to prepare for GATE, because all of them take admission in M.Tech from GATE score.

Hi Venkatesh,
I am having something for you, have a look.
Before the exam:
The meticulous study is the correct approach that can help you resolve all your doubts and attain lucid perception of various theories, concepts and their uses regarding the syllabus. Try to solve as many as mock test papers & previous years papers, especially 1-2 months before the exam, as it will give you a clear idea about the difficulty level, pattern, & how to allot the minimum time to solve a particular type of questions. This will help you know yourself, your capabilities & the field in which you are lagging. You should give at least 6 to 7 hours daily to your studies. The best way to prepare for the exam is preparing a time table and then sticking to it throughout the preparation tenure. Refer to standard books only, and prepare hand-written notes. During Exam:Always remember Time is the key to success. Learn to manage your time. Try to solve a question with maximum speed, allotting a very little time to it. Don't spend too much time on a particular question, it's better to move on and solve other questions. Try to attempt section first which you can do very fast. Don't try to attempt the questions which you don't know or don't know to solve. Keep negative marking policy always in your mind.

JEST is joint entrance screening test. It is conducted in the month of February once every year. Where can I write JEST exam? JEST exams are conducted across major cities of india, it is conducted in many cities like Ahmadabad, Aligarh, Allahabad, Bangalore, Mumbai, Nagpur, Pune, Raipur, etc. Eligibility for JEST:
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M.Sc/ME/M.Tech/MCA and related disciplines, interested in maths aspect with computer science will be considered for Ph.D programme.
-Talented B.Sc/BE/B.Tech graduates are eligible for Master's degree.
JEST is the exam via which students are selected for interview, JEST is conducted for Ph.D and integrated Ph.D programs for physics and computer science every year.
-GATE score cannot be used instead of written exam of JEST but it is used for shortlisting candidates for direct interview for Ph.D programs.