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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeDec 11th 2017
    • (edited Feb 6th 2018)

    I started a bare minimum at quantum probability (redirecting noncommutative probability space etc.)

    Some entries have long been secretly referencing such an entry, and I have cross-linked accordingly, for instance from von Neumann algebra and quantum computing.

    I had the feeling somewhere we already had a detailed account of probability theory dually in terms of von NNeumann algebras, but if we do I didn’t find it(?)

    • CommentRowNumber2.
    • CommentAuthorUrs
    • CommentTimeDec 21st 2017

    added the pointer to Segal 65 “Algebraic integration theory”

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeFeb 6th 2018
    • (edited Feb 6th 2018)

    added also pointer to the recent textbook Landsman 17.

    A neat quick introduction is Gleason 09. But at the moment the server with the pdf seems to be down. We should upload a copy to the nLab server. Does anyone have a local copy? (I didn’t save mine, it seems.)

    • CommentRowNumber4.
    • CommentAuthorDavid_Corfield
    • CommentTimeFeb 6th 2018

    The address is giving me the paper: http://www.math.uchicago.edu/~may/VIGRE/VIGRE2009/REUPapers/Gleason.pdf

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeFeb 6th 2018

    Okay, that’s strange, I still get no response from this address.

    Could you be so kind to upload a copy to the nLab? Or else to mail a copy to my private email address? Thanks!

    • CommentRowNumber6.
    • CommentAuthorDavid_Corfield
    • CommentTimeFeb 6th 2018

    Is that Ok, now?

    • CommentRowNumber7.
    • CommentAuthorUrs
    • CommentTimeFeb 6th 2018
    • (edited Feb 6th 2018)

    Thanks!!

    (I took the liberty of uploading it to the main web (here), instead of your personal web. That seems more robust against future changes, such as migrations.)

    • CommentRowNumber8.
    • CommentAuthorDavid_Corfield
    • CommentTimeFeb 7th 2018

    Can anyone upload to the main web?

    • CommentRowNumber9.
    • CommentAuthorUrs
    • CommentTimeFeb 7th 2018
    • (edited Feb 7th 2018)

    Yes. Sorry, I thought this was clear.

    Now I was about to point you to the HowTo, only to see that it didn’t have a section on file upload. Now I have added one:

    How To… Upload files

    • CommentRowNumber10.
    • CommentAuthorDavid_Corfield
    • CommentTimeFeb 7th 2018

    Ok, let’s hope the spammers don’t think to upload their nonsense.

    • CommentRowNumber11.
    • CommentAuthorTobyBartels
    • CommentTimeSep 10th 2018
    • CommentRowNumber12.
    • CommentAuthorTobyBartels
    • CommentTimeSep 10th 2018

    @ Urs #1

    I had the feeling somewhere we already had a detailed account of probability theory dually in terms of von NNeumann algebras, but if we do I didn’t find it(?)

    You may be thinking of Bayesian interpretation of quantum mechanics (now linked from this article) and its spin-off JBW-algebraic quantum mechanics, both of which have been discussed here before. Or for specifically classical probability and commutative real von Neumann algebras (or equivalently associative JBW-algebras), see measurable locale. There's not a lot of detail there on this subject, but some of Dmitri's posts to MathOverflow cited in the References are relevant.

    • CommentRowNumber13.
    • CommentAuthorUrs
    • CommentTimeSep 11th 2018
    • (edited Sep 11th 2018)

    Thanks, good point to cross-link these entries.

    • CommentRowNumber14.
    • CommentAuthorTobyBartels
    • CommentTimeSep 11th 2018

    Let me add that I'd love to see a succinct explanation of how to do classical probability theory using operators on von Neumann algebras, whether on the nLab or elsewhere, but I don't actually know one. Nor do I know enough to write one, although I'd like to learn enough.

    • CommentRowNumber15.
    • CommentAuthorUrs
    • CommentTimeSep 11th 2018

    I think that’s what the references Segal 65 and Whittle 92 are about.

    • CommentRowNumber16.
    • CommentAuthorUrs
    • CommentTimeJul 29th 2019

    added these pointers:

    diff, v20, current

    • CommentRowNumber17.
    • CommentAuthorDavid_Corfield
    • CommentTimeJul 29th 2019

    I added Bohr topos as a related concept, but maybe there something more substantial to say about states which are linear and positive only commutative-subalgebra-wise.

    By the way, do you still think that suggestion to bring Bohr toposes together with a layered dependent type theory – here – might work?

    diff, v21, current

    • CommentRowNumber18.
    • CommentAuthorUrs
    • CommentTimeJul 29th 2019

    but maybe there something more substantial to say about states which are linear and positive only commutative-subalgebra-wise.

    These are called quasi-states and Gleason’s theorem says that they are equivalent to actual quantum states. From the entry:

    In quantum mechanics, a quasi-state on an algebra of observables AA is a function ρ:A\rho : A \to \mathbb{C} that is required to satisfy the axioms of a genuine state (linearity and positivity) only on the poset of commutative subalgebras of AA.

    While therefore the condition on quasi-states is much weaker than that for states, Gleason’s theorem asserts that if A=B(H)A = B(H) for dimH>2dim H \gt 2, then all quasi-states are in fact already genuine quantum states.

    Notice that a quasi-state is naturally regarded as an actual state, but internal to the ringed topos over the poset of commutative subalgebras of AA – the “Bohr topos”. Therefore Gleason’s theorem is one of the motivations for regarding this ringed topos as the quantum phase space (“Bohrification”.) The other is the Kochen-Specker theorem.

    • CommentRowNumber19.
    • CommentAuthorDavid_Corfield
    • CommentTimeJul 29th 2019

    My #18 wasn’t a request for information - I’d read the Bohr topos entry. I was just wondering if it could be useful to a reader of quantum probability to be given a paragraph to encourage them to visit Bohr topos, rather than have a mere link there.

    • CommentRowNumber20.
    • CommentAuthorUrs
    • CommentTimeJul 29th 2019

    Oh, I see. Sorry. Sure, I’ll add a line.

    • CommentRowNumber21.
    • CommentAuthorUrs
    • CommentTimeJul 29th 2019

    okay, I have added a brief remark connecting to the Bohr topos (here)

    diff, v22, current

    • CommentRowNumber22.
    • CommentAuthorUrs
    • CommentTimeJul 29th 2019

    added “theory” to the page name

    diff, v22, current

    • CommentRowNumber23.
    • CommentAuthorDavid_Corfield
    • CommentTimeJul 29th 2019

    Great, thanks.

    I hadn’t noticed that interesting order-theoretic structure in quantum mechanics page before.

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