The Classical Channel

1:14 AM

0

Q: Are the Renyi entropies decreasing in the family parameter?

Are the Renyi entropies: $$S_\alpha=\frac{1}{1-\alpha}\log(\text{tr}[\rho^\alpha])$$ decreasing in alpha? Can I have a formal proof of this?

Alice

12:53 PM

0

Q: If $|\psi\rangle, U|\psi\rangle$ are known, how many pairs of such qubits are required to find the operator $U$?

Assume that we know a quantum state and the result of applying an unknown unitary $U$ on it. For example, if the quantum states are pure qubits, we know $|\psi\rangle=\alpha|0\rangle+\beta|1\rangle$ and $U|\psi\rangle=\gamma|0\rangle+\delta|1\rangle$. Then how can we compute the unknown operator ...

quantum-gate quantum-state quantum-information

Feeds

0

Q: How to build the two qubit basis?

If I want to define the basis in the form of $4$-vectors, how do I proceed to make sure they are orthonormal with one $1$ and three $0$ in each vector? Is it just by convention? Does it matter if I define them according to: $$|00\rangle = (1,0,0,0)^T ;\ |01\rangle=(0,1,0,0)^T ;\ |10\rangle = (0...

quantum-mechanics quantum-information mathematical-physics vectors

Alice

1:41 PM

0

Q: Construction of optimal ensemble to show quantum steerability

In Wiseman et al. (2007), in the process of deriving necessary and sufficient conditions for the steerability of some classes of states, the authors show (lemma 1, page 3) how to construct an optimal ensemble $F^\star=\{\rho_\xi^\star\mathscr P_\xi^\star\}$ such that, if this ensemble cannot expl...

entanglement nonclassicality

Alice

1:57 PM

0

Q: Is programming in quantum computer same as programming in quantum simulator in classical computer?

I just started programming in Q# and I wonder if the coding for Q# in classical computer would be the same as coding in a quantum computer. Obviously, these 2 kinds of computers work differently, so I guess the language must be working differently as well. Does this affect the coding part in any ...

programming q# language

Alice

3:33 PM

0

Q: Why does |PU − PV | equal <ψ|U† MU|ψ> −<ψ|V † M V |ψ>?

In QC and QI by Chuang and Nielsen they state that the P of an operation U acting on ψ can be reached by <ψ|U† MU|ψ>. I don't understand it. Can anyone explain it? And why do they equal each other?

quantum-gate quantum-state quantum-operation

Anonymous

4:28 PM

@glS I don't think it's necessary to close this as off-topic. The on-topicness of a question should not depend on whether or not it has already received an answer on another site. It's best to just add a note in the body of the question mentioning that it has cross-posted.

Anonymous

It's also possible that someone here will be able to come up with a more comprehensive answer that the one on Physics SE. So I don't see any convincing reason to prevent future answers. For similar reasons, I'm also very hesitant about closing questions as duplicates and mostly leave it to the discretion of the community.

Anonymous

6

A: What questions from the beta would be on-topic on other sites?

I have to close this catch-all question review thread as a highly inadvisable activity. First, if a particular question (or a larger subject space) becomes troublesome in actual practice, the merits of that topic should be raised and discussed in its own thread. Questions can and do get closed...

Anonymous

> Unless a question or topic space has been deemed off topic on this site explicitly, we have no cause to remove someone's content for another site, along with the reputation and ownership that goes with it.

Alice

7:01 PM

0

Q: Is it possible to create a superposition in IBMQ QISkit which has probability amplitudes |a|≠|b|?

For example, we can create a single qubit state with a polar angle of π/2 with the Hadamard gate. But, can we create a state such as this, where the polar angle does not equal π/2, in QISkit?

algorithm quantum-gate quantum-state quantum-information ibm-q-experience

glS

7:30 PM

@Blue I mean, ok, but shouldn't the OP at least try and make the question a bit different? Otherwise we are just duplicating questions. Should someone then post the same exact answer both here and on physics.SE?

Anonymous

@glS Of course, they should! But a new user usually doesn't know how they should tailor their question for our site. You can guide them in the comments rather than voting to close (alternatively, do both if you actually think the question classifies as "off-topic")! Another option is to edit it yourself.

Anonymous

If they spam with cross-posts, we can deal with that. But let's assume good intentions in the first few instances.

Anonymous

No, it's certainly not okay to copy the same answer over from there. That would be nuked instantly. But when it's an on-topic question we can keep it so that it can potentially receive good answers from a different set of audience too.

glS

8:54 PM

@Blue I was really not assuming bad intentions. I was mostly coming from the observation that when this sort of thing happens the OP generally loses interest in one of the two posts and doesn't really care about it being closed. For example, asking for clarifications generally leads to the poster simply telling you that the problem has already been solved elsewhere and so on.

to be clear, I don't really care about the "true intentions" behind the post. My point of view is that the usefulness of a post is 98% in the way it will help future googlers. In this regard, I'm not sure how much added value will there be in having the same exact question duplicated here. On the other hand, I also don't feel that strongly about it being closed, so if people prefer to leave it open I'm also fine with that

I guess the ideal would be to change the question in a way that at least does not make it an exact duplicate

Anonymous

@glS I'm sure you were not assuming bad intentions! I do agree with what you're saying. Anyway, here the bigger picture is: "we're trying to create a repository of high quality Q&As leaving aside individual differences and behaviors". So closing it would not really serve any purpose as such. In such cases, if you think it can be somehow modified to be made a bit more suitable for our site, then go ahead and edit it (if and when you get the time).

glS

@Blue but that's the thing though. If I post an answer that I think is good for the question here, why should I not post the same answer on physics.SE? It's not like it would be out of context there, and it would still answer the question properly (if it does here)

Anonymous

> If I post an answer that I think is good for the question here, why should I not post the same answer on physics.SE?

Anonymous

Okay, let's see this from a different perspective:

Anonymous

Say someone with a CS background (in the future) is looking for an answer to a specific question "X", which resides on both Physics and Quantum Computing. Upon googling for the keywords they find the same question on both the sites. So far so good. Now they open one and notice that the answers there are sorta skewed towards physicists.

Anonymous

9:03 PM

Whereas when they open the QCSE thread they see that the answer there is written from a computer scientist's or mathematician's viewpoint. In such cases, they have the choice of picking the answer which most is helpful for them. But if we strictly forbid cross-posting we're indirectly harming all such future visitors to our site. But now consider they find the same answer on two different threads. Does it help them any more? NO!

Anonymous

Our goal is to create a high-quality knowledge repository. Duplicate answers won't help us to that goal. But duplicate questions with answers from varied viewpoints and varied communities will.

Anonymous

I'd love "answer sharing" between sites. It would be great if the SE devs can come up with something like that in the future. I've always considered cross-pollination between scientific disciplines to be enriching for the individual disciplines as well.

Anonymous

I was just discussing this with the other mods on the TL. ^

Mithrandir24601

We're aware that guidance on this is confusing at best, misleading at worst, but yeah, there's generally no need to migrate something that's on topic (and otherwise suitable)

Anonymous

I mean, we should certainly see this from the wider perspective. Our site will serve as an educational tool for the generations to come! And we should do whatever it takes to make it a great tool. We're really building something for the future, collaboratively. One of the reasons you can see me editing questions and answers day in and day out.

Mithrandir24601

9:09 PM

Linking the questions by an edit/comment might be helpful though

Anonymous

9:30 PM

62

A: Feature Request: Non-game, no-edit Stack Overflow

People editing others questions only stands to curb user education (learning to ask better questions, use better/more-descriptive wording, etc) The history of the Internet is littered with the corpses of communities that thought they could demand compliance from new members without showing t...

Anonymous

Another very relevant post. Explains why editing is so necessary in communities like ours.

Anonymous

> The history of the Internet is littered with the corpses of communities that thought they could demand compliance from new members without showing them how. Editing is hands-on education for those willing to learn and a means of salvaging the efforts of those answering even when the asker never learns anything.

Anonymous

I always encourage editing and fixing over voting to close and downvoting, as far as possible!

Anonymous

However, I do certainly understand that's not always possible. That's okay.

Transcript for

The Classical Channel