Matt #1079:

“But I still don’t see how this affects are operational argument, which is independent of the details of Bob’s strategy – we only need to to be right about what Charlie (the protector) does.”

Yes, this is the crux; what Charlie (the protector) does is not a PM. For example, in your scheme, one get many inaccurate expectation value…[Read more]

Matt #1078:

Thanks for this clarification.

Shan

Hi Max and Ken,

Thanks for your comments! As to Ken’s question #1, I think the quantities measured by PMs are not probabilities. They are expectation values of observables.

As to Ken’s second question: yes, the argument, if valid, also establishes the reality of multi-particle entangled states. But this does not imply ehese…[Read more]

Thanks, Matt! If there’s anything that’s been written up on weak values in the Gaussian theory, please give me a pointer to it. I don’t recall anything like that in the original paper, but it’s been awhile since I’ve looked at it..

Hi Shan,

Apologies that I can’t participate at the scheduled time of your chat, but I have two questions that I can throw out now, and that we might discuss afterwards.

1) When you apply your revised ‘reality criterion’, you’re talking about predicting “with probability arbitrarily close to unity the value of a physical quantity”. But in this…[Read more]

Hi Shan,

Unfortunately your talk will be during a time slot when I will have my two young kids to look after. So I will not be able to chime in in real time. But I’ll be sure to check back later.

Also, I’m thinking that some of the points about the foundational implications of protective measurement we have talked about during Matt Pusey’s talk…[Read more]

Dear Ulrich,

It is tempting to again answer your points one by one. But I fear that this might not lead to more clarity in the end. So what I will do instead is focus on the issue of properties. I also intend this to be my last contribution to the online workshop.

According to QBism, measurements on nuclear spin components and measurements on…[Read more]

Ken #1081,

The best toy model for thinking about weak measurements is the Gaussian theory, because then you already have continuous variables to act as your pointer, the pointer can be prepared in a Gaussian state, and the “von-Neumann measurement” interaction is present in the theory.

A nice example for imaginary weak values is to prepare the…[Read more]

I meant the contexts from section 3 and section 4, but I see there’s quite a lot of work done on the operational aspects of weak measurements already, so how about we focus on section 4. Is there an analog that tells us something about general weak measurements in the Spekkens toy model, for instance? ( I’m particularly interested in…[Read more]

Ken #1074,

I’m afraid I don’t quite get your question. Which contexts are you talking about?

Cheers,
Matt

Shan #1070,

We definitely need to think more about which schemes are or are not equivalent to the original ones. (There is also a question of what equivalence means exactly – for example if one scheme requires classical post-processing of the data whilst another does the same processing “as it goes along”, does that necessarily mean they are not…[Read more]

Shan #1053,

What we do or don’t know has no bearing on which POVMs exist. Of course it may affect our choice of POVM – if we already know what basis the system was prepared in, we can measure it in that basis and determine the correct state. I don’t think anybody would argue that this establishes the reality of the wave-function. The claim is…[Read more]

Thanks, Matt, for that very clear piece! I don’t think I have much to add or contribute, although I will say that your arguments helped me reframe how I think about protective measurements, and as it happens it’s quite similar to how I’ve recently been framing weak measurements, with one key difference. Have you looked at weak measurements in…[Read more]

Dear Ruediger,

Many thanks for your detailed answers to my questions. I have a few comments, numbered 1 to 5 corresponding to your five answers.

1. Actually there are ways to assign probabilities to particle tracks (suitably defined), and your answer seems to accept that, having Alice making bets on Bob’s report about the tracks he saw.

2.…[Read more]

OK, Max. Have a good night! Best, Shan

Hi Shan,

Thank you for your reply, that’s helpful.

I will need to take a closer look at Matt’s notes myself. Tomorrow!

Best,
Max

Hi Max,

Thanks for your comments! I just noticed them. I am reading Matt’s notes about the toy model of PM.

I think your above worry in #1056 is right, which is still related to the limit problem we discussed in your presentation. I think I have two solutions: one is the new criterion, and the other is my PBR-like argument.

Yes, I still think a…[Read more]

To Shan #1028:

An example is a trapped atom, where the potential may not be known beforehand, but one does know that after a sufficiently long time the atom is to be found in the ground state.

At the risk of beating this horse to death: I would rephrase this to read “one does know that after a sufficiently long time the atom is to be found in…[Read more]