The Classical Channel

Q: Improving probability of spontaneous parametric down conversion

@Blue 'experiment' would be super broad, just like a 'theory' tag

Anonymous

@Mithrandir24601 I meant for questions like this:

Anonymous

5

As mentioned in an earlier question of mine, I am interested in using type one spontaneous down conversion (SPDC) in optical quantum computing. However, SPDC is a somewhat low probability occurrence - most of the photons pass straight through the crystals unentangled. What methods, if any, are th...

Anonymous

Maybe we could come up with a better name which is more descriptive but related to experiment

Anonymous

Not sure

12:02 AM

@Blue with a better name, I might be able to be convinced :P

Anonymous

Yeah, well, let's leave it for now

(I've also made some more tag edit suggestions, if you want to review)

Anonymous

I guess we'd need one for questions like: "I am trying to make a home-made 2 qubit quantum computer. This is what I did, etc. I'm stuck in this..." But well, such a situation hasn't come up yet

Anonymous

@Mithrandir24601 Sure, checking

@Blue Well... That's pretty much what @heather is trying to do, from what I've gathered :P

Anonymous

12:07 AM

Well, she is asking her questions in small chunks tho :P

Anonymous

Which is sort of good

@Blue Yep... SPDC can get very technical, very quickly

Anonymous

So the experiment tag isn't absolutely necessary, as of yet

Anonymous

Yeah, very true

Anonymous

The link I gave on her question about the alternatives to SPDC requires indepth knowledge of semiconductor physics

Anonymous

12:10 AM

(I didn't read it in full...just glanced through the main points it said)

Anonymous

Dozing time now. See you!

@Blue Night!

2:21 AM

Just made a post on meta.

2:33 AM

I think clarification on linking external websites is necessary. A lot of the questions and answers will use information from scholarly articles. Setting a standard for linking these articles would be beneficial. For instance @Blue commented on my earlier post, "always link to the abstract of a paper, rather than the pdf." Information like that would be good to know, but I do not see anything about it anywhere.

Q: Does Barkhausen noise affect the measurement of magnetic particle based qubits?

3:01 AM

1

Q1: I've tried to find out if Barkhausen noise affects the measurement of spin-wave excitations in magnetic particle material based qubits. I prefer implementations such as those described in "Magnetic qubits as hardware for quantum computers", rather than a true hybrid system such as described ...

quantum-computer qubit quantum-computing-models noise

Q: Should the tags 'qubit-state' and 'qubit' be merged?

6:54 AM

4

There are quite few tags with the qubit-state and qubit. Are these fundamentally different? Should the tags 'qubit-state' and 'qubit' be merged? If not, why are these things different? We should then update the tag usage to indicate this. If yes, then we should probably pick one to keep (I th...

discussion tags

3

Q: View counter on main site is lagging

The view counter on questions on the main site doesn't seem to get updated immediately as it does on other SE sites, or even in meta, here. I believe this is some software error on the developer's end. I've been actually observing this since Day 1 of the site, however I thought it would eventuall...

bug

4

Q: Site name not visible (transparent) in chat room

Could the dev team please improve the contrast here? The site name seems to be transparent and of the same color as the background in the region enclosed in red (in the snapshot below).

bug

1

Q: Is meta-physics a good tag?

I don't believe the tag meta-physics is a good one for this site. Firstly, such questions generally are more philosophy based, and thus don't really belong here, so having this tag seems to encourage off topic questions. Second, the only question that bears this tag is not really much better cate...

discussion tags

1

Q: External Website Links

Background Recently I noticed a few posts that link to external website links. These posts use the external links as the core of the answer. Example This is one example of a short post with an external website link: Example 1 Questions What is considered the proper usage of a external websit...

discussion moderation

7:39 AM

@Blue Yes, judging by my +2's, things are going well.

@Blue I think that experimental-results would be good name for this tag, if we want the tag

8:06 AM

@Discretelizard Based purely on my own opinion, I've accepted your edit, but I stand by what I said in that if you can think of a better name, I would personally rather have that used instead (this is just my own opinion, others may disagree etc. etc.). Also, as the discussion is ongoing in meta, consensus may well be that we don't want it at all, so we'll see if it stays

@Mithrandir24601 This is on philosophy?

@Discretelizard yeah

@Mithrandir24601 Ok, well, then my point stands. If you're on the fence, let it be.

8:27 AM

Btw, I'm curious. What's your 'impact score'? Mine's ~500 and my rep isn't even that high!

Ah, I can see the impact of others as well. Good. @Blue's on 1K already, it seems, very good.

Q: Why do classical bits perform calculations at a scale of 2n and qubits at 2^n? Where n=number of bits/ qubits

10:50 AM

0

What does one mean by saying that classical bits perform operations at the scale of 2n and quantum computers perform operations at the scale of 2^n? In both cases, n = Number of bits/qubits.

quantum-computer quantum-speedup

1:45 PM

Here's a question on the scope of this site: To what extent does it naturally cover "quantum information" topics? Previous to this site I'd have placed such questions under Physics.SE, but now I don't know.

@Semiclassical we decided that "Drawing a "line in the sand" this early seems rather unwise" so, ask and we'll soon find out!

(I.e. I believe we currently decide on a case by case basis)

2:00 PM

fair enough.

Anonymous

2:54 PM

@Semiclassical I think Quantum Information is fine for this site. Start by asking your questions here. If a considerable amount of people find it off-topic, we will then think about it. Anyway, we need more high quality questions here! Around 70% of the questions on the main site are beginner level as of now. (I'm personally more interested in theoretical quantum information and the mathematical aspects more than the engineering aspects)

Anonymous

We really need people like you to help improve the quality of the site! :P

Anonymous

@Mithrandir24601 I don't really feel like we should have a philosophy tag here. It feels like another orthogonal axis of classification which we don't really need. It's important to keep in mind that tags will be useful for future visitors to sort questions. Pretty sure that anyone seriously interested in the subject wouldn't look out for "philosophy" questions. Also, that tag has the possibility of attracting cranks.

Anonymous

@Discretelizard That's reasonable. You can edit that into the existing questions which you feel should have it.

Yeah, I may do that. Mostly I'm trying to figure out to what extent some stuff I've worked out is already known by the wider community. My strong suspicion is that people on the quantum information side of things know this stuff, but not necessarily people doing history/philosophy of quantum mechanics.

Anonymous

Great! :D

Q: Purpose of using Fidelity in Randomised Benchmarking

3:02 PM

(Stuff like correlation matrices and elliptopes.)

Anonymous

@Semiclassical I'm not really very inclined on having "philosophy of quantum mechanics"-type questions here.

Anonymous

14

Often, when comparing two density matrices, $\rho$ and $\sigma$ (such as when $\rho$ is an experimental implementation of an ideal $\sigma$), the closeness of these two states is given by the quantum state fidelity $$F = tr\left(\sqrt{\sqrt{\rho}\sigma\sqrt{\rho}}\right),$$ with infidelity define...

fidelity distance-measures randomised-benchmarking

Anonymous

Mithrandir's question is a very good example of the type of mathy questions we want

Yeah, definitely.

Anonymous

It's more of quantum information

Anonymous

3:03 PM

:)

Anonymous

@Semiclassical That should fit in here. We have a few people from Math Overflow hanging around

Anonymous

I'd say, just ask

Mmkay.

It involves matrices of expectation values e.g. $G_{ij}=E[\mathcal{O}_i \mathcal{O}_j]$

and to what extent one can characterize them as positive semi-definite matrices.

@Blue Sure, just remove them if you don't like it.

(more specifically, $G_{ij}=\dfrac{\langle 10|S_i^1 S_j^2 | 10 \rangle}{\langle 10|S_1^1 S_1^2 | 10 \rangle}$ )

3:10 PM

@Blue well, things like the physical Church-Turing thesis apparently have philosophical aspects (or something). Philosophy is a serious topic, just like history - people study history and philosophy of science, so I wouldn't go jumping the gun by saying that just because we don't do any philosophy in physics doesn't mean that it's not relevant. If people don't want it, I'm not going to complain, but I might start asking why we've allowed history questions

There's also the differences between questions like: "What does result X mean?" vs. "How long has X been known?"/"How does one derive X"?

The former can be subjective or philosophical, and thus not necessarily a great fit. The latter, by contrast, is technical and objective. (So long as there's agreement about how a result should be derived or who it should be credited to, of course.)

Anonymous

@Mithrandir24601 The problem with philosophy is that it will be opinion based most of the times....

Anonymous

While history has definite answers

ehhhhhh

Anonymous

Maybe we should decide it on a case by case basis

3:14 PM

I know what you're getting at there, but

Not everyone agrees on history :)

I think there's also a difference between "what does result X mean" and "what does result X mean according to interpretation Y"

Anonymous

@Mithrandir24601 If you wish, I'll make a meta thread about it. I get your point of view, but I think that tag has a huge potential of being misused

Anonymous

There's a reason why we don't have that philosophy tag on Physics SE

Anonymous

This debate has been done there before

A: Is meta-physics a good tag?

the latter is still possibly off-topic, but it's not quite so open-ended and opinion-based.

Anonymous

@Semiclassical True. But in 99% of the cases it will be possible to classify those questions under the already existing classifications. I wrote up a answer yesterday:

Anonymous

3:19 PM

1

These are the top definitions I come up with when I google "metaphysics+definition": the branch of philosophy that deals with the first principles of things, including abstract concepts such as being, knowing, identity, time, and space. abstract theory with no basis in reality So yes, I don't...

"metaphysics" is one of those words which is a bit of a headache

Anonymous

@Semiclassical I agree. But do we really need an orthogonal classification for those questions? I think a question of that type will fit it, but we don't really need to label them specially

I don't tend to think of metaphysics as a bad word in how I myself use it, but it's picked up a lot of bad connotations

Anonymous

What result X means according to interpretation Y is hard-core science

Anonymous

Doesn't look very opinion-ish to me

Anonymous

3:21 PM

Pull up facts and state conclusion

Anonymous

Although there might be some different possible answers

@Blue I think this is a bias that a lot of scientists have - there's an entire SE on philosophy. Having said that, if it's removed, I'm not going to care one way or the other, I just don't think it's a good idea to dismiss something because we're so used to dismissing it

the wiggle room there is to what extent a given community has its own splits in opinion, yeah

plus there is an argument to be made that, while "what result X means according to interpretation Y" is a worthy SE question, it's better suited for the philosophy SE rather than this one

Anonymous

@Mithrandir24601 I want to make it clear that I'm not against logical/hard-core philosophy. I'm against the soft-philosophy questions. Here's an example of a soft-philosophy question: philosophy.stackexchange.com/questions/50124/…, while this is an excellent hard-philosophy question: philosophy.stackexchange.com/questions/210/…

Anonymous

But, my question is: Do we really need to label such hard-philosophy questions specially when there are already other classifications under which they might fit in?

Anonymous

3:27 PM

If we do decide to have a philosophy label we have to make very sure that it is not misused

Anonymous

@Semiclassical Someone asked me couple of days back how to explain quantum bogo sort using the Everett's many world interpretation. That's a totally fine question imo

Anonymous

(although quantum bogo sort is a joke algorithm)

Anonymous

@Semiclassical There's a quantum-information tag now :)

@Blue yeah, soft philosophy questions could be a nightmare to deal with :/

Anonymous

@Mithrandir24601 That's exactly the possible mis-use I was speaking about...

Anonymous

3:35 PM

I'm not against having hard philosophy here. We really don't need to label them explicitly

@Blue so the question is: are you trying to predict things that might go wrong with such a tag, or is this a valid enough reason to not have it at all?

@Blue this is a bit more convincing :P

Anonymous

@Mithrandir24601 I think it's a good reason to not have it at all. Or else we have to make it very very clear that soft-philosophy is not welcome, which is quite difficult given that most people don't care to read tag descriptions

@Blue this is true

Anonymous

Cool, we're on the same page then :)

Q: Circuit of controlled-Unitary

0

Suppose we have a circuit decomposition of a unitary $U$ using some universal gate set (of your choice). Is there a direct way to write down the circuit of the corresponding controlled unitary $C_U$? For example take $U=i Y = H X H X$, as a circuit: We can replace the $X$ gates by $C_X$ (CNOT)...

circuit-model universal-gates gate-synthesis

A: Why is the complex number an integral part of physical reality?

3:44 PM

@Blue Related is this. This is a 'hard philo' question that is still not very suitable here, although I'd let it slide.

5

Are we answering the right question? You touch upon an interesting point, but I have the feeling that your question isn't specific enough yet to reach a proper resolutions. Others have argued that 'complex numbers' aren't necessary for quantum mechanics. While I agree with their arguments, I thi...

Oh whoops, linked my answer by accident. Ah well, I like my answer there

@Blue Yeah, but this means we put it in and immediately see when people can't read.

Anonymous

@Discretelizard Hmm, that doesn't seem very "hard" to me. Nor does it seem possible to logically prove an answer to that question, or prove it with facts, etc

@Blue True. Although the answers can be decent

Some bad questions have good answers

Anonymous

@Discretelizard That question looks like an edge case. Anyway, I'd let the community members decide whether to close it or not, should such a situation come up.

Anonymous

I'd just not specially label them, as there doesn't seem much need

Q: Accepting Nominations — Who should Moderate♦ this site?

4:05 PM

@Blue Yes, lets just see if others think they should be tagged and just don't touch it if they do

FINALLY

1

Ideally, Moderators♦ are elected by the community, but until the community is large enough to hold a proper election, we will be appointing three provisional Moderators to fill those roles. We need your help. Please nominate folks you would like to see become provisional moderators for this site...

discussion featured moderation

4:44 PM

@Discretelizard I find most of your tag edits to add the "experimental-results" tags wrong. For example, quantumcomputing.stackexchange.com/questions/53/… is not directly about experimental results

@glS Well, than go fix it :) ?

That's what happens when you retag en masse. Collatoral.

@Discretelizard of course, I'm voting to accept/reject accordingly, I'm just wondering why you think that tag is appropriate there

@glS Being too speedy

@Discretelizard I don't like rejecting others' contributions without proper reason

Most retags without clear comments are too speedy

Well, that's the reason

Good that you asked, though!

4:45 PM

@Discretelizard oh ok. What do you mean exactly with "mass retagging" here?

@glS I just created, like 22 edits for only tags. Mostly for the new experimental-results

wasn't there already an experimental tag? I thought I added one at some point

I also still don't understand your use of quantum-computing-models. For example, why is this question about quantum-computing-models?

it doesn't refer nor need any specific "QC model", which in my mind are things like superconducting architectures, ion-trap stuff, optics, etc

@glS In my mind, models are theory. What you're talking about are computer implementations

@glS No idea

then I don't understand what you mean. Model as in what?

@glS A model, like a Turing Machine is a model. An adiabetic quantum annealer. A gate based universal quantum computer

If you have a better name, feel free to suggest

4:53 PM

but then, what is not included in such a tag?

everything is expressed using some such "model"

5:21 PM

@glS Not really. Some questions aren't about the model. Such as those asking for experiments with real quantum computers

Oh and forgive me for mentioning this, but it is rather curious that someone who literally was stopped by SE from editing so much is universally disliked as a potential mod. I didn't want to say this, but I'm afraid that I won't be staying for long if you don't want me to moderate. For community moderating is all I'm doing. So, I guess this is a good opportunity to get rid of me.

5:40 PM

Oh and one more thing: We need 3 MODS! So ehh, if you just downvote, you'll be seen as a community with unreasonable standards and ehh, well, let's just hope in the end there will be at least 3 people with a positive score?

@Discretelizard so should any non-experimental result be tagged in such a way?

@glS No, of course not. In particular, if we have quantum-algorithms, specifying a model is usually redundant.

@glS Also, some questions have clearer tags, such as qubit or something else more specific

I mean, this is a bit like an algorithms on CS. Almost all questions get it, some don't, most need more tags

Q: Can quantum algorithms be better than classical algorithms in classical simulation?

1

I'm wondering whether even if we cannot create a fast quantum computer, simulating quantum algorithms can be a reasonable method for classical algorithms. In particular, I'd like to see any results on this. Second, the next logical step would be to 'cut out the middleman' and see if we can remov...

quantum-speedup quantum-algorithms performance classical-computing

0

Q: Do we need [error-correction] of the [fault-tolerance]?

I am wondering whether the tags error-correction and fault-tolerance can/should be merged. They seem to relate to the same topic: prevention/correction of errors. What is your opinion towards merging these tags?

discussion tags tag-merge

3

Q: Accepting Nominations — Who should Moderate♦ this site?

Ideally, Moderators♦ are elected by the community, but until the community is large enough to hold a proper election, we will be appointing three provisional Moderators to fill those roles. We need your help. Please nominate folks you would like to see become provisional moderators for this site...

discussion featured moderation

7:09 PM

@Feeds This was asked hours ago! Come on @Feeds, you can do better!

Anonymous

@Mithrandir24601 Yeah, something's wrong with that

Anonymous

Cache problem probably

Anonymous

On private beta sites I guess it doesn't refresh as often

simulation bqc circuit-model cryptography d-wave measurement memory-space

@Blue I know IPS' Introverted Meta Man (love that name) is slow, but this is on another level

Anonymous

lol

Anonymous

7:17 PM

BTW I think someone should write up a nomination for Nat. He has contributed significantly and is very knowledge (from what I've seen)

Anonymous

Nat

706 20

Anonymous

I wanted to nominate Daniel but he mentioned that he doesn't want to run for mod

Anonymous

Also:

Anonymous

Niel de Beaudrap, Oxford, United Kingdom

448 9

quantum-computing-models architecture error-correction experimental-results fault-tolerance measurement noise

Anonymous

Maybe I'll write up for them if it's not done by tomorrow

Anonymous

7:20 PM

*knowledgeable

@Blue that's a shame :/ There are a fair few people that I can spot that could be good...

Anonymous

Yeah. He's busy :/

@Blue Yeah, of course :P I'm also busy, but no so busy that I don't have any time - I went through that in undergrad and decided that it wasn't worth the mental destruction it caused

Anonymous

Heh. I understand. :P I have my exams coming up next month, so I'll not be writing much answers/questions anymore during that time, but will probably continue the community activities

Anonymous

This as a hobby serves me as a refreshment

7:31 PM

@Blue This as a hobby is actually semi-relevant to my PhD :)

Anonymous

Haha, true

Anonymous

I guess I too want to pursue my masters/PhD later in this area, mainly theoretical/mathematical aspects of QI with some bit of quantum engineering (if I get a chance i.e.). The main reason I love it is because being it's so interdisciplinary and I don't have to necessarily give up my interest in pure mathematics or theoretical CS!

Anonymous

But that's a long time away :P

Anonymous

I should focus on completing my undergrad first XD

@Blue ... Or just make it part of your undergrad :)

Anonymous

7:40 PM

@Mithrandir24601 Yeah, trying to :P

For me, deciding to do physics over CS was the really hard part, so I've managed to make an effort to at least head in a direction where both a important

Anonymous

Sounds similar to my worries ^ ;)

Anonymous

Guess I'll sleep a bit early today. Biya for now!

@Blue Night!

8:09 PM

@Mithrandir24601 Want to learn more CS? I can teach if you'd like it.

@Discretelizard Thanks for the offer, but I've got enough learning to do during the day-time!

@Mithrandir24601 Haha, I can see that.

You know, I was planning on creating a 'teaching Physics CS' chat where I'd start by looking at all misconceptions on CS (4 as of now) I've seen around here.

But there are plenty chats as is. And you can always go to Computer Science

10:17 PM

I updated my post: quantumcomputing.meta.stackexchange.com/questions/89/…

Hopefully this makes things more clear as to what the thread is about.

i nominated myself for mod.

i'd be more than glad to answer any questions or concerns =)

@heather Does reputation matter in regards to rep on Quantum Computing SE?

10:34 PM

@Daniel what exactly do you mean by that?

I suppose, it's good to have a minimum amt of rep - that shows active participation in the site, and some level of understanding of the topic the site is based on.

on the other hand, for example, on Physics.SE, some of the highest rep users aren't mods - they don't want to be.

so you don't need to have the highest rep ever to be mod.

@heather haha, yeah I wasn't clear was I... I guess I was trying to point out that reputation isn't a criteria to being a mod.

@DanielBurkhart oh, I see what you mean. Yes, reputation isn't a criteria, but higher reputation shows that a. you've had experience with privileges, including mod/maintenance privileges, b. shows that the site can trust you, to some extent, and c. shows that you are active on the site, all of which are qualities a mod should probably have.

out of curiosity, why do you ask?

I just felt like your post focused a little too much on reputation and not on actual criteria.

@DanielBurkhart I see. Would you prefer I added more about my cv/meta/etc experience?

@heather I think you could make your case a little better if you gave it a little more focus on why you think your a good fit for moderator. You have some very good posts, I would point them out and give examples of how you have participated on meta and review queues.

10:43 PM

okay, thank you, i appreciate it! @DanielBurkhart

i will make those edits.