(My thread disappeared, I guess it was to do with the server problems discussed elsewhere. This is a repost.) About 8 years ago I left a Ph.D. programme in computational particle physics to join a financial trading startup company. They offered me a really good stock option package to be their high performance computing guy. But, they went bust when everything collapsed and I ended up being made redundant with pretty much no notice period. Then I got a job (after some very lean times) for a big trading company doing more or less the same thing (but with a lot less freedom). I joined this forum because I am starting to get really interested in physics again (as well as the arrival of a new boss at work that I've alluded to in another thread... How to deal with cranks? - in real life, which I'm hoping you can all help with given the crank ratio around here!). I've been paid incredibly well over the last 5 years and I've saved up enough money to support myself for an unfunded Ph.D. and then some. So, I want to ask: what areas of theoretical physics are showing promise at the moment? I'm not keen on String Theory, but anything to do with Quantum Information is intriguing. Extra info in response to a comment somebody made: I prefer the kind of physics that might be able to predict something new that can then be measured or exploited. I like the thought of working in a team with theoreticians and experimentalists, hence why I'm drawn to quantum information because it seems a lot of things could be implemented by a good optics group. I did an undergraduate degree which had more quantum mechanics than most, then did my 4th year honours at a different university specialising in advanced quantum mechanics and computational particle physics. My honours project was computational particle physics on a big computing grid and this is what my Ph.D. was going to be in (hence the reason why I was picked up by the startup because grid computing experience was pretty rare in those days). -- Your problem is that you really *do* have a sense of honour, and you really *do* care about trust and loyalty. Don't blame me for knowing you so well.
I'm about two years into a PhD in the general area of quantum information. My impression of the field is still a bit limited - I don't know what everyone is doing or what all the areas of research are (I know next to nothing about quantum computing for example and have a rather sketchy idea of the current state of experimental work) - but I still might be able to help. On the theoretical side, there's increasing interest in something called "device independent" quantum information processing. The basic idea behind this is to do something like quantum key distribution or randomness generation, but use a measure of quantum nonlocality such as a Bell test to prove security and correct functioning. It's called "device independent" because it's possible to certify that these protocols work correctly without having to assume anything about how the apparatus works. In device-independent QKD for example, to some extent you can allow for the possibility that it's an eavesdropper that has given you the equipment, and still prove that you can generate a key securely. Because of this, there's a lot of work studying device-independent protocols and device-independent state certification, and quantum nonlocality in general. Example papers: http://arxiv.org/abs/0903.4460, http://arxiv.org/abs/0908.0503, http://arxiv.org/abs/0911.3427, http://arxiv.org/abs/1203.2976. There's been some work on quantum entropy measures and their operational interpretation and practical application. Example paper: http://arxiv.org/abs/1009.2015 (proves the latest in a series of entropic charaterisations of the uncertainty principle, which allow for a rather neat security proof of the BB84 quantum key distribution protocol). There's been some work on semidefinite programming heirarchies (an optimisation technique with applications to numerically solving some quantum physics problems). Example paper: http://arxiv.org/abs/0903.4368. Some more computer science-oriented researchers have been looking at pictorial descriptions of quantum operations and gates based on category theory, with applications to quantum computing. Example paper: http://arxiv.org/abs/0906.4725 (describes a graphical "calculus" that the authors present as a "higher level language" to the Dirac formalism's "assembly"), There's also some research being done on interpretations of quantum theory, and studying what kinds of alternative models may or may not be able to make the same predictions as quantum theory, though obviously this is purely theoretical stuff that's never going to see any practical applications. Example paper: http://arxiv.org/abs/1201.6554 (just to give an idea; there's been some followup discussion on this result, including another paper by one of the same authors explaining some limitations of the first paper). ...and probably much more that I either don't have in mind right now or simply haven't heard of. This list is inevitably heavily biased toward what I and some of my colleagues are working on. Clicking on some of the author names and looking at their other publications should also give you an overview of what people are thinking about and doing in quantum information. Non-exhaustive list of researchers/group leaders I keep hearing about: Antonio Acín, Nicolas Brunner, Jonathan Barrett, Stefano Pironio, Serge Massar, Matthew McKague, Valerio Scarani, Sandu Popescu, Renato Renner, Nicolas Gisin, Andris Ambainis.
