Matt Leifer » APS

Foundations at APS, take 2

mleifer — Tue, 06 Mar 2007 23:30:11 +0000

It doesn’t seem that a year has gone by since I wrote about the first sessions on quantum foundations organized by the topical group on quantum information, concepts and computation at the APS March meeting. Nevertheless it has, and I am here in Denver after possibly the longest day of continuous sitting through talks in my life. I arrived at 8am to chair the session on Quantum Limited Measurements, which was interesting, but readers of this blog won’t want to hear about such practical matters, so instead I’ll spill the beans on the two foundations sessions that followed.

In the first foundations session, things got off to a good start with Rob Spekkens as the invited speaker explaining to us once again why quantum states are states of knowledge. OK, I’m biased because he’s a collaborator, but he did throw us a new tidbit on how to make an analog of the Elitzur Vaidman bomb experiment in his toy theory by constructing a version for field theory.

Next, there was a talk by some complete crackpot called Matt Leifer. He talked about this.

Frank Schroeck gave an overview of his formulation of quantum mechanics on phase space, which did pique my interest, but 10 minutes was really too short to do it justice. Someday I’ll read his book.

Chris Fuchs gave a talk which was surprisingly not the same as his usual quantum Bayesian propaganda speech. It contained some new results about Symmetric Informationally Complete POVMs, including the fact that the states the POVM elements are proportional to are minimum uncertainty states with respect to mutually unbiased bases. This should be hitting an arXiv near you very soon.

Caslav Brukner talked about his recent work on the emergence of classicality via coarse graining. I’ve mentioned it before on this blog, and it’s definitely a topic I’m becoming much more interested in.

Later on, Jeff Tollaksen talked about generalizing a theorem proved by Rob Spekkens and myself about pre- and post-selected quantum systems to the case of weak measurements. I’m not sure I agree with the particular spin he gives on it, especially his idea of “quantum contextuality”, but you can decide for yourself by reading this.

Jan-Ake Larrson gave a very comprehensible talk about a “loophole” (he prefers the term “experimental problem”) in Bell inequality tests to do with coincidence times of photon detection. You can deal with it by having a detection efficiency just a few percent higher than that needed to overcome the detection loophole. Read all about it here.

Most of the rest of the talks in this session were more quantum information oriented, but I suppose you can argue they were at the foundational end of quantum information. Animesh Datta talked about the role of entanglement in the Knill-Laflamme model of quantum computation with one pure qubit, Anil Shaji talked about using easily computable entanglement measures to put bounds on those that aren’t so easy to compute and finally Ian Durham made some interesting observations about the connections between entropy, information and Bell inequalities.

The second foundations session was more of a mixed bag, but let me just mention a couple of the talks that appealed to me. ~~Marcello Sarandy~~ Alioscia Hamma talked about generalizing the quantum adiabatic theorem to open systems, where you don’t necessarily have a Hamiltonian with well-defined eigenstates to talk about and Kicheon Kang talked about a proposal for a quantum eraser experiment with electrons.

On Tuesday, Bill Wootters won a prize for best research at an undergraduate teaching college. He gave a great talk about his discrete Wigner functions, which included some new stuff about minumum uncertainty states and analogs of coherent states.

That’s pretty much it for the foundations talks at APS this year. It’s all quantum information from here on in. That is unless you count Zeilinger, who is talking on Thursday. He’s supposed to be talking about quantum cryptography, but perhaps he will say something about the more foundationy experiments going on in his lab as well.

Foundations at APS

mleifer — Tue, 14 Mar 2006 21:57:39 +0000

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.

Support the APS topical group

mleifer — Thu, 22 Dec 2005 05:22:07 +0000

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.