Thanks for putting this all together! I just wanted to expand on Michael’s suggestion of quantum computing. There is increasing interest in industry to provide quantum computing tools. A few standouts that I see publishing/talking at conferences are
These companies are advertising their product as a tool for machine learning (among other things). Further, these companies are all just cloud service providers. Their goal is to get their product online as fast as possible for use by whoever can afford it. I would need to do more research to figure out how quantum machine learning impacts x-risk (it could be small assuming machine learning on classical computers develops quickly but scaling quantum hardware is slow), but playing the right role in these companies could be very high impact.
I also wanted to add a possibly off-topic note of caution about physics research. I am currently a grad student in experimental physics, so this is possibly overly-pessimistic about university research (grass is always greener on the other side). However, I would be cautious optimizing your resume completely to do research as a professor, which is what I think many physicists do. Academic positions are extremely competitive and best suited to people who are interested in the research for its own sake rather than for the impact it has. So I think it is important to either be very sure how excited you are about physics for its own sake (does it match the level of your young professors?) or to build a resume that could also veer towards your favorite non-physics direction, if needed (e.g. taking a few classes in writing good code, doing an internship in industry).
[epistemic status: anecdotical] on not doing physics
If you want to build a resume in a non-physics direction, as Christopher suggests, and you are early in your career, don’t wait too long to explore alternatives. I personally made a mistake by not exploring alternative options enough before I finished my master’s degree (in Europe).