The h Bar

@vzn yes. You can only measure point on sphere using repeated measurement on identically prepared copies of system.

But that's all assuming we're talking about projective measurement.

obe

12:25 AM

@BernardoMeurer is rufus legit?

David Z

Anyone care to help me diagnose a MathJax issue in our other chat room?

All I need is for someone else to post a message with some MathJax in it in the other room

Bernardo Meurer

@obe Yes

it's the usual tool

@DavidZ Done

@dbassett hi. This weekend might be best.

But you can just ask here and I'll answer asynchronously.

Random question: Why a black body must radiate EM waves corresponding to its temperature, why we cannot have a black body that only absorbs but not radiating. Is it because a nonradiating black body will violate the second law of thermodyanmics since there are a lot more microstates in the EM field thus energy tend to be redistributed there?

12:44 AM

@Secret Those are two good reasons.

Another good reason is that electromagnetism, which governs EM waves, is time-symmetric and doesn't distinguish between absorption and emission.

I see

1:40 AM

The IceCube data suggest that one species of neutrino may comprise exactly equal amounts of two neutrino “flavors.”

Heat driven transitors as sensors

@Secret What a low-information press article. But the meeting presentation it describes seems to be available online.

[Obligatory eye-rolling about the APS "April" Meeting occurring in January goes here]

@DanielSank ok, but is there any other kind of measurement? anyway the newer "quantum surrealism" experiments seem to claim to measure pts on the bloch sphere...

Plastic and sunlight solar vapor generator made more efficient with cardbon dipped paper, may help solve water problems in disaster ridden areas

Nick Alexeev

We've got a cross-stack dupe: EE.SE version, Physics.SE version. Which stack shall we merge them on?

1:56 AM

@NickAlexeev Looks like it's been on Physics for a couple of days without much interest, but the EE version has a couple of useful-looking comments already. Should I migrate it to you or is there another way to merge?

@rob I am not very sure how to read the data. Which slide suggests the $\nu_{\mu}$ disappearance it is a mix of two other flavors?

@Secret Slide 9 is an exclusion plot. Presenter's analysis suggests that $|\Delta m_{32}^2|$ and $\sin^2\theta_{23}$ lie in the black oval. "Best" point is the black cross but it's probably wiser to treat the entire oval as more or less equally likely. Other ovals are constraints from other experiments.

The mixing angle between the second and third flavor states is $\theta_{23}$, so $\sin^2\theta_{23}=1/2$ corresponds to equal mixing.

Hmm interesting, Slide 12 also has the data fitted to an inverted hirarchy, so either $\nu_{\tau}$ or $\nu_{e^-}$ are equal mix of $\nu_{\mu}$ and the other flavor

Looks like one result (Noνa 2016, normal hierarchy) favors $\sin^2\theta_{23}!=1/2$, but mostly my interpretation of that plot is "we still don't have good constraints on $\sin^2\theta_{23}$"

@Secret The IceCube constraints for normal hierarchy (slide 9) and inverted hierarchy (slide 12) look basically the same, which says to me that they're not terribly sensitive to the hierarchy.

Nick Alexeev

@rob The other way is for me to migrate it to you. Ether way.

2:12 AM

@NickAlexeev It's yours: electronics.stackexchange.com/q/284126

Bernardo Meurer

@NickAlexeev An electronical engineer here!

Nick Alexeev

@BernardoMeurer Well... What can I say... EEE can happen to anyone.

Bernardo Meurer

@NickAlexeev I'm still in uni for it :P

Well, I'm a Computer Engineer

Really, juxaposition of a high quality thing with an undesirable cost next to a high quality thing with a desirable cost and a low quality thing with desirable cost lead us to choose the high quality undesirable cost thing...?

@vzn yes, weak measurements.

2:31 AM

Learn about a wolf population's diet and distribution via the endoparasites

Circularly polarised spin momentum locked light coupled to quanutm emitters allow directional emission of radiation. Useful in preparing photonic diodes and circulators

@Secret That one's a review article: nature.com/nature/journal/v541/n7638/full/nature21037.html

@DanielSank ok. was guessing that. hasnt anyone proposed that weak measurements obtain the legendary "hidden variables" long sought/ questioned in QM? ie real, imaginary part of psi? if not, why not? my understanding is that, based on what someone told me (years ago), Majorana may have proposed something like this ages ago...

Q: What would happen to a single light wave if mechanically cut in half?

0

Imagine a single light wave with a 1 meter length. This light wave goes through a hole in a wall. Before the entire light wave passes through the hole, the hole is closed so that only half of the light wave actually gets through. What happens to the part of the light wave that gets through? S...

visible-light

It will just... continue...?

2:55 AM

Electron movement studies in liquid helium for quantum computing applications

@vzn No. Nobody has proposed that weak measurements obtain hidden variables because it doesn't make any sense.

On the other hand, there have been demonstrations of violating Bell-type inequalities in experiments using weak measurements.

Do violating bell inequlities always imply entanglement, or there are non entanglement type configurations that also violate bell inequality?

@Secret I'm genuinely confused by a lot of the Bell-inequality literature. What Bell proved had two parts: (a) a particular model for locally real observables gives weaker correlations than quantum entanglement, and (b) any other hypothetical locally real model gives weaker entanglement than QM, but without a constraint on how much weaker.

But most of the literature seems to analyze data using the CHSH (Clauser et al) version of Bell's inequality, which assumes the particular model (a). It seems like there's some unexplored parameter space.

3:10 AM

There's also something called quantum discord, which encompass all types of quantum correlations besides entanglment. I have not read that in detail though

Linear spring model for modelling swimming of microorganisms and drug delivery capsules

This is not a surprising conclusion, but can we siphon this extra energy somehow...?

@rob Let's put it like this: the only really interesting thing that can happen is someone does an experiment which is inconsistent with the theory we already have.

That has not happened.

Bell's inequality says "if you measure XYZ and get more than 2, then that's compatible with quantum mechanics and not with hidden variables in the particular way that I have described them".

Now, that "particular" was is actually rather general, so in fact violating Bell's inequality excludes quite a bit of "design space" (very appropriate phrase).

School start early=sleepy students

yes, people have been discussing this for years.

In the US, the elementary schools start later than high schools, which is ridiculous.

I mean, I think I know why we do that:

It's ok for teenagers to get home early, before mom/dad are out of work, because they can take care of themselves (or go to a job).

Younger kids need after school care or parents.

That's my guess.

3:35 AM

@DanielSank That's a good explanation. But the experimental descriptions bug me. The entanglement data typically lie somewhere between the CHSH limit and the QM prediction. The analyses typically say "the classical behavior is excluded, and we're probably inconsistent with QM because of experimental imperfections." But I usually don't see the disagreement with QM quantified in terms of measurable parameters. The possibility that neither prediction is quite correct doesn't get considered.

... At least, that was my impression when I spent some time thinking about this semi-seriously, ten years ago. It's a big literature and I don't know much of it.

I wonder what these driven time crystals will be useful for...

In the future, try driving them at relativistic speeds and see if we can make a spacetime crystal

sciencedaily.com/releases/2017/01/170130083231.htm

Why are holograms from a holographic universe, unlike the holograms we made, are real instead of incorporeal?

4:15 AM

@rob agreed! great way to put it, & a way few others would phrase it. have been looking into the "unexplored parameter space" for many yrs, think have found a solution there. =D but, difficult to formulate exactly.

@DanielSank EPR1936 argues QM is incomplete. think that a physical demonstration that QM is incomplete would be far more than "really interesting". think weak measurements are increasingly essentially/ exactly that...

@rob think you have zeroed into the heart of the matter like few others. there are recent experiments/ claims/ writeups of "loophole free bell tests" but think theres more to the story...

@vzn One problem is that the EPR paper attracts so many know-nothing cranks that the bar for expressing confusion about it is quite high.

bottom line: after very long study think its possible to create a purely classical experiment that violates the bell inequality. some scattered researchers are now coming to the same conclusion. but its now regarded as a minority-to-fringe pov. think that will slowly be overturned in years ahead. think it will eventually resolve the "hidden variables" concept in favor.

@rob by some measures, the most cited physics paper of all time. x% will be cranks.

4:45 AM

gfycat.com/MellowWebbedGhostshrimp

@rob Until pretty recently, there weren't systems with very highly controlled control and very high accuracy state measurement. Because of the quantum computing field, there are now systems with both.

Nowadays, we can make entangled states and understand the deviations from idea pretty damn well.

It's just that, honestly, most of us aren't particularly interested in publishing Bell state stuff because it feels old hat (and because to be interesting you have to close the spacelike separation loophole which is hard in a dilution refrigerator).

4:59 AM

Yes, the weak measurement techniques were just starting show up when I was last looking seriously. Like I said, there's a lot of literature that I haven't thought carefully about.

Zeilinger is very interested in the spacelike separation side of things. Here's a new trick. I've only looked at the news story, not the PRL.

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