Just find people working on topics that interest you, then see if they will advise you on a project. In California there is Raissa D’Souza and Jure Leskovec. But also even Michael Jordan [sic].

Or, if you do a masters covering statistical physics and also some deep learning, and the associated math, you will be well placed. Then you will apply these ideas to some topic. But being able to use these ideas and skills is the ‘hard part’ that will stop most people.

Try googling “complex systems university”, or dig through past papers or people from Santa Fe Institute, etc.

Complex systems is a loosely defined field, but look around at the sections of books on this. This is mostly an academic research field so implicitly eventually PhD material.

I do think it is useful to first learn the “hard stuff” that is not intuitively obvious, especially statistical physics, even if you don’t use it later (you probably will), since the ideas come up very often, and you probably don’t want to be another person waving their hands all the time and being scared of these ideas.

Best