how to masters/PhD in physics for an electrical and electronics engineer?
From what I read on the forums, it's hard to go to a theoretical physics group for physicist, let alone for engineer.
I am an EE too, and I want to pursue a degree in physics, but something related to
quantum computing, which (I think) needs a little physics than does theoretical physics.
I believe the same applies for experimental programs.
The idea is that you well need a lot of math and pure physics to get the minimum
understanding of topics like strings theory / quantum gravity / standard model.
So if I were you, I would apply for an applied / experimental physics program, and
there you could take your electives in theoretical physics (you will need the consent
of your adviser, though).