The h Bar

Q: Quantum circuit for a W state

0

Can someone specify a quantum circuit that will deterministically output the $3$-qubit $W$ state, if the input to the circuit is $|0,0,0 \rangle$? Or, is there a quantum circuit with a different $3$-qubit input state that will output the $3$-qubit $W$ state deterministically? I am looking for an ...

quantum-information entanglement quantum-computer

I forgot how one experimentally put two given states into superposition, though I remember about polarisers and wave plates rotating states along one of the 3 directions

1:17 AM

[Ramblings] Entanglement: Wavefunctions of subsystems become correlated, resulting in an overall wavefunction that cannot be factorised (hence also the probability distributions and distributions of other observables)

this is a valid way to look at it since the wavefunction has a deterministic evolution

skullpetrol

1:39 AM

[Ramblings] :: ramble, ramble, ramble...::

Q: Can superfluids communicate faster than light?

1:55 AM

0

According to this video: https://www.youtube.com/watch?v=ueVTzEB3tJ8 A superfluid "flows without friction" and "all of the atoms in a superfluid are in the same quantum state." What strikes me as odd is the statement "all [the atoms] have the same momentum, such that if one of them moves, they a...

faster-than-light superfluidity

Obviously not, but is a huge tank of superfluid nonlocal (in the sense of position, not in the sense of signalling), given how it is in effect one single quantum state...?

ffden-2.phys.uaf.edu/212_fall2003.web.dir/…

skullpetrol

Led Zeppelin - Ramble On

Hmm, I am guessing, if a small region of a tank of superfluid is perturbed by some local interaction, the atoms in said region would end up in a different state and thus that region will stop behaving like a superfluid

2:16 AM

I think I either need to ask a PSE question, or Acuriousmind about this, as superfluid is clearly a single quantum state, so you cannot really perturb just a small region of a tank of superfluid without changing the quantum state (which is the whole tank), or is it...?

2:30 AM

actually, screw that, let me dig deeper into PSE...

2:58 AM

Fun fact: Without the Greenhouse effect,the temperature of earth would have been -18℃

A: In a radioactive Bose-Einstein condensate, would all the atoms disintegrate simultaneously?

1

There are several ways to destroy a Bose-Einstein condensate. The most common is temperature, which is why BECs are all low-temperature phenomena. For instance, helium becomes superfluid when a large fraction of the atoms enter the same quantum state, which happens around $\mathrm{2\,K = \frac16\...

Ha, so that means a tank of superfluid locally perturbed will result in the atoms in that region to be knocked out of the condensate, instead of having the whole tank of fluid changed at once

vzn

3:52 AM

← just saw this with 2 beautiful latin women & have no other place ot brag about it :| :P imdb.com/title/tt4465564 happy valentines day everyone hope you have someone special to share it with too :)

4:34 AM

Dumb question, but does arXiv only have scientific papers?

0celo7

4:56 AM

@SirCumference what other kind of papers are there?

@0celo7 You know what I mean

Like, does it have notes

0celo7

@SirCumference Yes

@0celo7 Huh really?

0celo7

You asked a question and I gave an answer.

You don't like that answer, so it was either a bad question or you knew the answer already

5:19 AM

@0celo7 What? No, I was just surprised

@0celo7 Humanities papers. Arts papers. Just because other disciplines of human endeavor run on a different philosophical substrate doesn't mean people aren't communicating their scholarship that way.

@SirCumference Well, you'll find some papers in economics up there. Some people would argue that 'science's is where they patently prevaricate'. ::tip's hat toward to Randall Monroe::

@dmckee I was thinking along the lines of notes, even textbooks, etc.

SFU Choir - Every Major's Terrible

More emphasis on "papers" than "scientific"

@SirCumference The mission of arXiv concerns itself with preprints—things destined (or hopefully destined) to be published as papers. I don't think the moderators would look too kindly on someone using it for things that are clearly not papers, though you could possibly slip in some edge cases.

5:34 AM

@dmckee So if someone keeps a preprint on arXiv, it gets published in a journal, and the author updates or revises it, it's not likely that the paper will be updated on arXiv?

@ACuriousMind Videos are better for the same use cases as demonstrations in class. For communicating the dense mathematical detail that is needed for mastery text is king (or queen or gender neutral monarch).

@SirCumference I lot of arXiv pre-prints get a text up-date after the reviews come in. I've updated one just before submitting the revised text.

But they don't generally have a post-publication life.

@dmckee Not sure what you mean by "post-publication life"

@SirCumference I mean the pre-print isn't changed after the journal version is available.

Oh. Well, thanks

The only case I can think of for that is a retraction of a large part of the claim.

David Z

5:42 AM

@dmckee PhD theses too. That's actually encouraged by the administrators.

Don't give up the day job: Kristen Stewart's academic paper on AI in film making dismissed as 'brief and more like a case study' by experts / dailymail

@DavidZ Yah. Fair-enough. Because most thesis are never 'published' in a manner that makes them actually available but they are (or are suppose to be) some genuinely new work.

vzn

+ dont forget stuff coauthored by top hollywood celebrity o_O

in theory salon, Feb 9 at 1:57, by vzn

+ 100+ ~~claims~~ proofs (lol!) on P vs NP o_O win.tue.nl/~gwoegi/P-versus-NP.htm

6:09 AM

Make sure to cross check often. Daily mail is not a reputable source even according to wikipedia

6:52 AM

@SirCumference you do get books and lecture notes on the Arxiv.

7:07 AM

@vzn Does KS have a science degree or something ?

@JohnRennie Er, ok

Kind of confused now

@SirCumference why?

Some people say it's merely for papers, others say it's more

Wikipedia says it's for preprints

It was intended to be for preprints and it is still mainly for preprints.

However other stuff that people think may be useful does find its way onto the Arxiv.

"Quantum field theory may be understood as the incorporation of the principle of locality (“Nahwirkungsprinzip”)"

Good old Nahwirkungsprinzip

7:18 AM

It is quite common for lecture notes from courses given at the better known summer schools to be uploaded to the Arxiv, and very useful they are too.

Huh, neat

See for example this search

@JohnRennie Hm, how can you tell if something is an actual paper or just notes, before looking at it?

Entries for papers will normally say what journal they are being published in.

@JohnRennie I don't see any way to distinguish this paper from these notes.

7:27 AM

In this case the summer school lecture notes were published (in AIP Conf.Proc.1287:99-104,2010) so this really is a journal pre-print.

Ok, clearly I'm naive because I didn't think journals accepted lecture notes...

AIP Conference Proceedings

Bear in mind that journals publish all sorts of stuff like reviews and conference proceedings as well as original papers.

In this case is was published in a journal that specialises in conference proceedings:

AIP Conference Proceedings is a serial published by the American Institute of Physics since 1970. It publishes the proceedings from various conferences of physics societies. Alison Waldron is the current Acquisitions Editor for AIP Conference Proceedings. In addition to the series' own ISSN, each volumes receives its own ISBN. AIP Conference Proceedings publishes more than 100 volumes per year, with back-file coverage to 1970 which encompasses 1,330 proceedings volumes and 100,000 published papers. == Scope == In 2010 broad subject coverage included biophysics, plasma physics, geophysics, polymer...

@JohnRennie So even if it's not original information?

Journals routinely publish review articles ...

Well clearly I've been confused...

7:32 AM

The main content of most journals is indeed original research.

user228700

Hi, everyone :-)

But other publications like reviews and lecture notes can be very useful and it's good that they are published.

@Kaumudi.H Hi :-)

@Kaumudi.H Hi :)

@JohnRennie So, then again, how can you tell if a publication is original research or lecture notes before reading it?

@SirCumference it would normally be obvious from reading the abstract.

> Comments: 6 pages, 3 Figures. Talk given at CINVESTAV's Advanced Summer School of Physics 2009. Mexico City, Mexico, 27-31 Jul, 2009

Lecture notes and review articles have a lot of subsections, and generally more than 10-20 pages

Original research articles are generally shorter and more on reporting the data or model

7:41 AM

Gotcha

@JohnRennie Unrelated question, but confused. More cosmology (hopefully the last I'll deal with for a while): is the comoving distance to the edge of the observable universe increasing at the speed of light?

@SirCumference I'm working for the next half hour or so. Back soon ...

19. Physics | Fluid Statics | Pressure Distribution in an Accelerated Frame | by Ashish Arora

8:17 AM

@SirCumference the comoving distance to the particle horizon is at $\eta c$, where $\eta$ is the conformal time: $$ \eta = \int_0^t \frac{dt'}{a(t')} $$ It isn't obvious to me this is increasing at the speed of ight.

help

8:43 AM

Why in this video force applied by liquid is not considered

9:55 AM

That's one scary looking perturbation. It's just 1st order?

11:26 AM

20 February is going to be an interesting day:
- AMA with heather (which is my first time attending one)
- UK parliament will debate this petition (https://petition.parliament.uk/petitions/171928) :-))

can we ask heather nothing but questions about UK policies

Is it possible to ask a question without adding to the pool before?

Some questions I want to see a spontaneous answer

I've definitely missed the past AMAs :(

well you can also ask us anything right now

It's not like any of us are actually famous

We couldn't even get Lumo to do one

Q: productivity and self improvement questions

I can't ask you something like this now

But still have some questions that I can ask

For example, I like to see @DanielSank s answer to this

I don't why interesting questions get downvoted....maybe because they're somewhat controversial

Physics Meta

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You can ask productivity and self improvement questions related to programming or computers on software engineering stack exchange . See for example this question , http://softwareengineering.stackexchange.com/questions/141860/should-i-be-concerned-that-i-cant-program-very-fast-without-google W...

discussion support questions tags

11:44 AM

@Mostafa you can ask anything during the AMA. The idea of soliciting questions is to make sure we have a reasonable number of interesting questions, but the list isn't meant to be exclusive.

The previous AMAs have all tended to run out of questions towards the end so there should be plenty of opportunity to ask extra questions.

that's great, thanks.

also about its time

it's 2AM for me

:(

Where are you that it's 2 AM

it's 3 AM in California

are you in the middle of the pacific

Tehran

Do you mean 2 PM

Let me see again :/

Its 10pm, right?

10pm GMT

Tehran is GMT +3:30

user228700

12:21 PM

Random question: Troye Sivan, anybody? (Music)

Troye Sivan - HEAVEN ft. Betty Who

Who

user228700

...OK :-P

user228700

For anybody even remotely interested to listen to some "new" music:--

user228700

12:36 PM

Is there a query for the most downvoted answer on a site? I'm curious if anyone ever made it below -20.

Duffield did

@Slereah Nope, lowest is currently at -17 net score

A: Is there an elegant proof of the existence of Majorana spinors?

-17

Is there an elegant proof of the existence of Majorana spinors? No. Because they don't exist. The neutrino is not a Majorana spinor. It's a Weyl spinor. See Dirac, Majorana and Weyl fermions by Palash Pal. He said “the neutrinos had to be uncharged because of conservation of electric charge,...

Hm

I remembered a -21 answer

I guess it got deleted

hehe @ACuriousMind

I know it is not on physics^

12:52 PM

@ACuriousMind Did you try data explorer ?

@anonymous My SQL capabilities are non-existent

And searching for existing queries is rather difficult, you must happen to guess the exact words someone used in their title.

@ACuriousMind You could ask Kenshin to make a query on Data Explorer. He seems to be good at it. I learnt to use the data explorer a year back and now I forgot it all. Anyway, why do you want to find the most downvoted answer ? :D

@ACuriousMind

Example: data.stackexchange.com/stackoverflow/query/36660/…

Q: Do we need Maxwell's Equations since they fail to account for an experimental fact at least in one occasion?

-28

This question is an outgrowth of What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)? , where @sb1 mentioned Faraday's law. However, Faraday's law as part of Maxwell's equations cannot account for the voltage measured between the rim...

electromagnetism maxwell-equations

12:57 PM

@anonymous I'd like to compare the lowest values on different sites with each other, I'm interested how different communities favour downvoting but not deleting vs. deleting.

@Mostafa Wow. Strictly speaking not an answer to my question since that's a question, but good find ;)

I guess you went to the last page of the votes tab.

Loong

@ACuriousMind Oh, yes, that could be interesting. That was one aspect when I asked this question on meta.chemistry: meta.chemistry.stackexchange.com/q/3484/7951

> Should such answers be deleted, or wouldn’t it be more to the point if they stay – with downvotes that clearly indicate the assessment of the community?

This might help some what math.stackexchange.com/search?q=is%3Aanswer+score%3A500..

@anonymous Hm, I guess I'd need to adjust the PostTypeId field. Is 0 the setting for an answer? Or is it 2?

I don't know how to filter for negative votes