@vzn Basically it means that the forwards and backward propagation directions correspond to left and right polarization handedness (propagation direction is locked to polarization)
@0celoñe7 Also, that line reminds me of my old friends. Whenever I would miss a meeting between friends or something, they would call and spew out some slangs and end with "Are you alive?" (in native language, of course)
@Mostafa (understand inherent QM ambiguity here...) they seem to be able to detect individual photon events at each side, that seems to be a major pt of the experiment... are all the "dots" in the diagrams capable of shooting out photons?
Acuriousmind have left for the day, I guess I need to wait for his reply tomorrow. I hope my proposed realistic setup is sound enough to demonstrate my argument that those coefficients are to be interpreted as probabilities...
@Mostafa will have to work from arxiv version, cant get access to Nature version, but how many photon sources are there? each dot is a photon source right? trying to follow how many dots there are (oh Nature figs are open, let me get to that...)
@vzn They're most likely holes in the structure of the material - they way that the holes are 'placed' creates (in this case) a wave guide, so each hole isn't by itself a waveguide, but the location of each hole forms a waveguide overall
@vzn At a very quick look, there doesn't seem to be a dot 'hard-made' into the structure of the top layer of the material, but it could very easily be a dot above or below - is it a simulation?
I'd use frozen peas. Just cook them according to the instructions on the pack. Drop them into boiling water and cook for whatever the pack says - about 5 mins I think.
@Mithrandir24601 yeah wondering about that myself. anyway that diagram is showing a single "photon event" right? or can they control which direction (left/ right) the dot emits in? or is it random?
@ACuriousMind well, I'd say the purported approach goes against the purpose of the measurement postulate: probabilities arise in QM only when one takes a measurement
@vzn There are (if I'm remembering correctly) things you can do to help make the dot emit in a certain direction, but in general, you can't arbitrarily control the direction a dot emits a photon in
@Mostafa Wow, wow, wow - once a photon is coupled into the waveguide, then you can force it to go in a certain direction. Coupling into the waveguide is the harder bit :P
@Semiclassical how will you write down a hamiltonian for the system of 3 polarisers controlled by a random number generator that I proposed above as an argument that the hamiltonian is to be interpreted as an ensemble of hamiltonians?
@vzn I haven't read the thing, but it appears that you can 1. Make different polarisations go in different directions (i.e. polarising beam splitter) and 2. have different polarisations have different coupling strengths to the waveguide
@Mostafa coupling itself may (or may not) have a high probability of occurring, but often, getting the dot to emit a photon so that the photon reaches the waveguide is where there are going to be further coupling losses
@vzn nonreciprocal means having different behaviors for different propagation directions. like a diode. (It absorbs light that goes from left to rigtht, but not right to left)
@vzn and "chiral" here means left and right propagating modes necessarily have opposite polarization directions. By coupling this waveguide to atoms that interact with only one polarization type (LCP or RCP) you make this chiral waveguide a nonreciprocal one which can be used as an optical isolator.
Hello h Bar: Perhaps you can help develop a half-baked idea of mine. A handful of tags are prone to misuse and overuse, most notoriously perhaps the mathematical-physics tag. Idea: "Protect", say, the mathematical-physics+ tag with, say, a plus in the end. (I put the word "protect" in quotation since there are no actual reputation restrictions on the use of tags.) All appropriate mathematical-physics question should be tagged with this new "protected plus" tag.
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No questions should be tagged with the old "unprotected" mathematical-physics tag. Next let the "unprotected" mathematical-physics tag be a synonym of a master tag, say, please-delete-this-tag. The idea is that experienced users will soon learn to add the plus to "protected" tags (it is suggested from the pop-up menu), while questions with please-delete-this-tag tag may need attention from editors. See also this meta post.
@AccidentalFourierTransform Interesting tidbit: there is a harmonic function on $B(0,1)\subset\Bbb R^2$ such that $\frac{1}{2}\int_{B}|Du|^2\,dx=\infty$
@Mostafa anyway really nice find, have been tracking this area fairly closely for years... are you doing experiments in this area? trying to remember do you have undergrad degree?
@0celoñe7 which really sucks, bc there is a certain consensus that $\text{variational problem}\equiv \text{oasis of PDE's where everything works just fine}$
@Mostafa think DS will like it, "right down his alley," maybe will mention it to him someitme (havent seen him for awhile)... seems like it could be quite applicable to his area etc
@AccidentalFourierTransform It tasted pretty good to me! They were glacé cherries not fresh cherries. You can't cook fresh cherries in a cake. They just go mushy.
"choose a sequence of smooth domains $\Omega_\epsilon\subset\Omega$ with $\Omega_\epsilon\uparrow\Omega$ and $\mathcal H^{n-1}(\partial\Omega_\epsilon)\to \mathcal H^{n-1}(\partial\Omega)$ as $\epsilon\downarrow 0$"
@vzn I'd like to know more about its possible implications in qunatum information and related areas. every papers talks about how important this could be in that area but I don' know why and how.
@Mostafa dont quite follow whole thing myself but basically polarization direction is not considered controllable in QM, it seems they are nearly controlling it. they are talking about a (eg) "deterministic CNOT gate" which almost sounds like an oxymoron wrt (prior) QC theory.
@Secret Quantum mechanics doesn't allow you to say "I have a device controlled by a random number generator". There are two possible descriptions of the system you have set up here: 1. You don't care about the quantum mechanical description of the random number generator and just care about the output state of your polarizing device. Then you just start with the density matrix that's given by the mixed state defined by the probabilities for the electron state you've written down.
2. You care about the quantum mechanical description of the random number generator, in which case you have the generator and the electrons unitarily evolving as an interacting system, resulting in an entangled state. Tracing out the state of the generator then reproduces the mixed state from approach 1. In practice, it is impossible to give a full quantum mechanical description of your "random number generator", so you just go with approach 1.
Anonymous
@Mostafa In short: Everything that is tasty is bad for your health :D
@Qmechanic I'm not entirely sure what this is supposed to achieve - what will stop the same hapless users that currently tag the wrong questions with math-phys from tagging the wrong questions with math-phys+?
@ACuriousMind I have simulated a system where I have a section of gates (currently only Paulis for testing purposes, but if I can get time, I plan to extend this to a different set of gates), with the gate operation to be performed depends on the outcome of a QRNG, so it does require interaction of quantum-classical-quantum, but it is 'a device controlled by a random number generator' to some extent...
@Mithrandir24601 I'm not saying such systems don't exist. I'm saying the proper theoretical description in quantum mechanical terms is either my option 1 or my option 2, and not the strange hybrid that Secret tried to do.
"choose a sequence of smooth domains $\Omega_\epsilon\subset\Omega$ with $\Omega_\epsilon\uparrow\Omega$ and $\mathcal H^{n-1}(\partial\Omega_\epsilon)\to \mathcal H^{n-1}(\partial\Omega)$ as $\epsilon\downarrow 0$"
@Qmechanic I like where you're going with this but my concern is that, in this example, people who want to use mathematical-physics will just start typing it and choose what appears in the autocompletion popup, which will be mathematical-physics+. The effect being that it's not really going to solve the problem.
(cont. from above) Perhaps a better approach (for now) is to pipe the tag feed into this chat room, or another room dedicated to posts to review. We get the same effect of putting questions where people have tried to use the tag in front of reviewers who can tell whether it's appropriate, without introducing an extra level of indirection.
@ACuriousMind Also, in case it isn't clear, I don't think either blue or me or Yashas take any offence to that. (We are obviously not the ultra-nationalist type of guys)
@Sid Quick reminder: just as a general principle, even if people here don't take offense to something, that doesn't automatically make it appropriate for chat. (Though I don't mean to imply that this particular usage is or isn't appropriate.)
@ACuriousMind and @David Z : Yeah, like I said: A half-baked idea. Your inputs needed. Or perhaps it in practice slows down the tag misuse just enough...Should we test it?
@Qmechanic Oh, I missed that @ACuriousMind raised much the same objection I did. Whoops. Well, I'm always up for testing, I just have my doubts that it's going to fix things.
For a test, I suppose we create the new tags mathematical-physics+ and please-delete-this-tag, then set up the synonym, but do not convert existing mathematical-physics tags. Then we can let things sit for a while and see how the tag usage patterns after the switch compares to the frequency at which mathematical-physics was used before it.
If we decide that it's not working, we can reverse the changes with our existing tag-mapping tools, as long as no other synonyms point to please-delete-this-tag.
For testing purposes, I think it makes sense not to make any special effort to expose please-delete-this-tag to reviewers just yet. That way we can get a baseline comparison of tag usage patterns.
I know other sites have tag notices (I forget the real name), i.e. popups that show up when someone tries to use a tag, containing some information or warnings about the tag usage.
What are tag warnings?
Tag warnings are meant to provide users with just-in-time information to help them avoid mistakes that are common for the tag they’re using.
Here’s what they look like:
To see a tag warning in action, begin asking a question on Stack Overflow and tag it with sql. (Mor...
and the two tags will show up on the autocomplete anyway, with one of them synonym'ed to please-delete
If I was a new user, I know which one I'd choose
That said, tag warnings on mathematical-physics and mathematics sound like really good ideas
You know what would really be great, though? A review queue for that kind of thing
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I.e. if a user has three positive-score questions on (tag), then they can use it without problems. Until they do, though, all their posts get sent to the first-posts queue with a notice that says "This post uses the watched tag (tag). Please ensure that it's being used correctly."
That notation was brought up in a lecture in QFT last year. I point blank refused to use them and the lecturer's response was along the lines of "I don't blame you - I find it ridiculous as well"
@DavidZ/@Qmechanic/@ACuriousMind I think the ideal thing sounds like a feed into this chatroom - new tags will get misused like the old. I think @EmilioPisanty's idea of a review queue is best, and it's the feed into this chatroom idea that sounds closest to that.
Tag notices sound good too.
But if I recall correctly, the tag excerpt already has a warning.
@EmilioPisanty and others: Thanks for the feedback. Perhaps you are right. I have created a test for the mathematical-physics and general-physics tags.
A review feed is an interesting idea. Concening tag notices: Versions of this have already been long in place (in tag wikis/info) with seemingly no visible results.
@AccidentalFourierTransform : The DeWitt's index notation before and after the symbol shines when working with theories with fields of arbitrary Grassmann-parity.
What are tag warnings?
Tag warnings are meant to provide users with just-in-time information to help them avoid mistakes that are common for the tag they’re using.
Here’s what they look like:
To see a tag warning in action, begin asking a question on Stack Overflow and tag it with sql. (Mor...
