I returned this weekend from the meeting on Foundations of Probability and Physics at the University of Vaxjo in Sweden. There were many interesting talks, so I'll just mention a few of them that I found particularly inspiring.
– Giacomo Mauro d'Ariano explained his axiomatization of quantum theory, inspired by observations from quantum state and process tomography. One of the nice features of this is that he gives an operational definition of the adjoint. Why the observables of QM should form an algebra from an operational point of view has been a topic of recent debate amongst foundational people here at Perimeter, so this could be a piece of the puzzle.
– Rüdiger Schack explained what it might mean for quantum randomness to be "truly random" from a Bayesian point of view, using the concept of "inside information" that he has developed with Carlton Caves.
– Philip Goyal gave another axiomatization of quantum theory. I'm not sure whether the framework he uses is that well-motivated (especially the sneaky way that complex numbers are introduced). On the other hand, one of his axioms has the flavor of an "epistemic constraint", which gels nicely with ideas that have been expressed earlier by Chris Fuchs and Rob Spekkens.
– Joseph Altepeter gave another excellent talk about the state of the art Bell inequality experiments currently going on in Paul Kwiat's group.
– John Smolin outlined speculative ideas that he and Jonathan Oppenheim have developed that applies the concept of locking quantum information to solve the black hole information loss problem.
Here’s my list of the highlights of the conference season for foundations this year:
April 28th-30th: New Directions in the Foundations of Physics – University of Maryland.
- Foundations of Quantum Information and Entanglement.
May 29th-June 2nd: Beyond the Quantum – Lorentz Centre.
June 4th-9th: Foundations of Probability and Physics 4 – Vaxjo.
July 9th-14th: Quantum Structures 2006 – Malta.
- This is annual meeting is usually interesting. Unfortunately, attendance is by invitation only.
28th November – 3rd December: Quantum Communication, Measurement and Computing – Tsukuba.
- The big “quantum logicy” meeting.
- This is really a quantum info./optics meeting, but it’s a big one and there’s usually some foundationsy talks as well.
Personallly, I’ll definitely be at Vaxjo, Malta and Tsukuba, so I’ll see you there if you’re going.
I’m currently at the APS March Meeting, where there were two sessions on Quantum Foundations on Monday. I am pleased to report that they were well attended. Hopefully, this marks the start of an increased involvement of the APS in the field.
The second session was particularly interesting, so here’s a short summary of what we heard:
- Invited speaker Lucien Hardy outlined his Causaloid framework for general probabilistic theories without a fixed background causal structure. It is hoped that this might lead to a new path for developing a theory of quantum gravity.
- Chris Fuchs gave a shortened version of his usual talk, focussing on the role of symmetric informationally complete POVMs in his approach to quantum foundations.
- Terry Rudolph presented an extension of Rob Spekkens’ toy theory for dealing with continuous variable theories. This has lots of features in common with QM, but has a natural hidden variable interpretation, being a resticted version of Liouville mechanics.
- Rob Spekkens showed how two seemingly different notions of “nonclassicallity”, nalely negativity of peseudo-probability distributions and the impossibility of a noncontextual hidden variable theory, are actually the same within the new approach to contextuality that he has developed.
- Nicholas Harrigan outlined an approach to quantifying contextuality that he has been developing with Terry Rudolph.
- Joseph Altepeter, from Kwiat’s group, gave an interesting presentation on their current state of the art photonic Bell inequality experiments.
- OK, I have to admit that I was getting tired at this point and skipped out for a talk, so I have no idea about the next talk. Apologies to Giuliano Scarcelli.
- There then followed two talks about decoherence from Diego Dalvit and Fernando Cucchietti, collaborators of Zurek and Paz respectively. This is an important topic for many interpretations of QM and the results looked solid. However, I’m not an expert on this stuff.
- Ruth Kastner, who was due to deconstruct the now famous Ashfar experiment, was unfortunately unable to attend due to illness, but Ashfar was here to give his side of the story instead. The experiment is interesting at least because it has made quite a few physicists think about complimentarity and foundations in general a bit more deeply. Personally, I agree with Kastner’s analysis, but Ashfar disputes it.
- Jeff Tollaksen outlined a new way of measuring the “weak values” introduced by Aharonov and collaborators. I didn’t follow the details of the construction, but look forward to reading the paper.
- Caslav Brukner outlined his work with Zeilinger on an “information based” approach to quantum foundations. It’s not my personal favourite amongst such approaches, but gave plenty of food for thought.
Well, foundations at this meeting are pretty much finished after that. There are still a few interesting quantum information sessions before the end of the week, but I can leave other bloggeurs to deal with that.
As you may know, the American Physical Society has recently opened a topical group on Quantum Information, Concepts and Compuation, which covers the foundations of quantum mechanics within its remit (under the “concepts” heading I suppose). There will be a special session on the Foundations of Quantum Theory at the APS March Meeting in Baltimore this year.
Although the abstract submission deadline has passed, I’d like to encourage everyone involved in quantum foundations to attend. The APS has not always looked favourably on foundational studies and it has been difficult to get foundations papers published in their journals in the past. The topical group could open the way for a new era of respectability for the subject within the APS, so making sure that the special session is well attended seems like a very good idea to me. In any case, besides the political point, the talks are bound to be interesting.