Physics PHD problem

Hello,
I am hoping to work in quantum computing, but the universities I want to attend don't offer a PHD in it. Should I go for a PHD in quantum physics or theoretical physics instead? What's the next best thing?

What do you mean "offer a PhD in it"? As in, there isn't a PhD called "PhD Quantum Computing"? Because that's irrelevant what the "name" of your PhD is, what matters is your project.

If you mean "those universities do not have any faculty researching in quantum computing to supervise my project in quantum computing" that is a big problem and suggests you are approaching the PhD wrong. You need to look for where the individuals who are significant in your specific area (i.e. quantum computing) are and apply to a PhD there, where they are.

What do you mean "offer a PhD in it"? As in, there isn't a PhD called "PhD Quantum Computing"? Because that's irrelevant what the "name" of your PhD is, what matters is your project.

If you mean "those universities do not have any faculty researching in quantum computing to supervise my project in quantum computing" that is a big problem and suggests you are approaching the PhD wrong. You need to look for where the individuals who are significant in your specific area (i.e. quantum computing) are and apply to a PhD there, where they are.

Yes, I meant exactly that, by 'offer a PHD in'. So, the choice between say, particle physics and theoretical physics doesn't matter then .. or?

The name of the PhD is irrelevant, what matters is the project itself. That IS the PhD. Anyone in your field will gauge your PhD work based in the project, not the name of the qualification. For those outside the field it's irrelevant to have any more description than "PhD in *general subject area*"

You're focusing on the wrong things here. You need to be finding those specialists in your specific area of research interest and aiming to do your PhD project supervised by them. What the actual degree name is will be secondary to at least the project title if not the project itself.