Отиди на
Форум "Наука"

Направи си сам - установка за сплетени частици


Recommended Posts

  • Модератор Инженерни науки

Направо давам статията в оригинал, а после ако трябва..

Пояснявам, защото потребителите са хора всякакви - не става дума за квантова телепртация. Говорим само за източник на сдвоени частици и детектори дето ги доказват.

How to Build Your Own Quantum Entanglement Experiment, Part 1 (of 2)
By George Musser | February 8, 2013
|
rm-60.jpgQuantum entanglement experiments are not something you can buy in the science kit aisle at Toys 'R Us. The cheapest kit I know of is a marvel of miniaturization, but still costs 20,000 euros. In the past month, though, I've put together a crude version for just a few hundred dollars. It's unbelievably simple--so simple that it barely works, let alone produce reliable results. But the thought of observing spooky action at a distance using homebrew equipment is so novel and exciting that I'd thought I'd share it with all you tinkerers, makers, hackers, and science-fair contestants. I got the idea last fall while building a supersimple cloud chamber. I was having trouble seeing particle tracks in my initial designs and wanted to check whether the radioactive materials I had scrounged really were radioactive. So I dug out a pair of Geiger counters that Aware Electronics in Wilmington, Delaware, gave me years ago for a post-9/11 review of consumer radiation detectors. Each time you hear a Geiger counter click, it has detected a single particle--which, in the case of gamma radiation, means a single high-energy photon. It struck me that the Geigers might substitute for the single-photon detectors that account for much of the cost of that EUR20,000 system. Doing a literature survey, I found that the very first entanglement experiment, performed by Ernst Bleuler and H.L. Bradt and independently by R.C. Hanna in 1948, used Geigers. It was the precursor of better-known work by Chien-Shiung Wu and Irving Shaknov, who reproduced the results using more sensitive detectors. In a strange twist of physics history, these researchers didn't associate their work with entanglement per se, let alone with Einstein's puzzlement over the phenomenon. Several years after the fact, theorists David Bohm and Yakir Aharonov realized that the experiments had breathed life into the famous EPR thought experiment ofEinstein, Boris Podolsky, and Nathan Rosen. Today, physics students at Caltech, theUniversity of Edinburgh, and elsewhere routinely perform the Wu-Shaknov experiment. But what about the rest of us who lack the resources of such august institutions? With the encouragement of David Prutchi, who practically invented the category of amateur quantum physicist, I decided to try to recreate the Bleuler-Bradt experiment in my basement workshop. The parts I use are:
  • two Aware RM-60 Geiger counters
  • disk of radioactive sodium-22
  • 1-inch-diameter plastic tube and wood plugs
  • Aware coincidence box
  • Geiger-to-iPad interface box (built from Radio Shack parts)
  • iPad running Geiger Bot app
  • cables for the above
  • lead can
  • two aluminum bars
Besides being cheap, Geigers have two major advantages as single-photon detectors. First, by detecting gamma rays rather than visible or infrared photons, they don't require darker-than-night conditions, which are the bane of optical entanglement experiments. Second, it's easy to buy sources of entangled gamma-ray photons. A small disk of radioactive sodium-22 runs $80, compared to $1,400 for a source of entangled optical photons. When the sodium atoms decay, they give off antielectrons, or positrons, which in turn annihilate with nearby electrons to create entangled pairs of gamma-ray photons. (As someone raised on Star Trek, I got quite a thrill ordering antimatter over the Internet.) Na22.jpgThe disk is rated as safe to handle, although it's not something you'd want to carry around in your pocket. At a distance of about a foot, its emission is comparable to the background level in my basement. The gammas spray out equally in all directions. The disk is also designed to let positrons escape from one side, in case you want some. I use a short wooden dowel to block these errant particles, as well as hold the disk in place inside a plastic tube. Theory says the entangled gammas in a pair fly off in exactly opposite directions, so I look for them by placing a Geiger on either side of the sample. Paired photons should cause both Geigers to click in unison. To count these simultaneous hits, I wire the Geigers to Aware's coincidence box (nothing more than a NAND gate, a standard electronic component), plug the c-box output into the mic jack of an iPad using a simple interface, and run an app called Geiger Bot. In pre-iOS times, Sci Am's Amateur Scientist columnist, Shawn Carlson, hacked a pedometer to accomplish much the same. Before hunting for entangled photons, I test the Geigers and c-box by measuring the background radiation--specifically, cosmic rays. When a high-energy particle from deep space hits Earth's atmosphere, it shatters into a fusillade of particles, notably muons, that rain down upon the ground. A muon will rip through both Geiger counters and register as a coincidence. You can tell you're detecting cosmic rays, rather than some other form of radiation, because the coincidence rate depends on the Geigers' positioning. Stacked one of top of the other, the devices register particles traveling vertically downward, and Geiger Bot counts about 3 coincidences per minute. This value matches estimates of the cosmic-ray flux for such a setup. Lined up horizontally side by side, the Geigers become insensitive to muons from on high and the coincidence rate drops by a factor of 100. (If you're a cosmic-ray geek, or bored, you can watch my readings on the Cosm data-logging website. Please let me know if you put your own cosmic-ray detector online.) Occasionally, the system also picks up spurious coincidences: two unrelated particles that just so happen to hit both Geiger counters at nearly the same time. For cosmic-ray detection, this is a non-issue; in the absence of any radioactive materials, each Geiger clicks only 20 times per minute on average, so a day might pass before both go off simultaneously by chance. When you're working with radioactive samples, however, the effect becomes significant, since the Geigers are clicking hundreds or thousands of times a minute. The rate of accidental coincidences scales up with the square of the Geiger readingsand, in Bleuler and Bradt's experiment, was comparable to the rate of genuine coincidences. It's unfortunate that the two rates are similar--it means any detection of entanglement will be marginal at best. But this source of error is unavoidable when using Geiger counters. Pricier kinds of detectors have sharper time resolution and pick up fewer chance overlaps. Having tested the electronics, I'm ready to start the experiment. In the next post, I'll describe what I found.
  • George Musser is a contributing editor at Scientific American. He focuses on space science and fundamental physics, ranging from particles to planets to parallel universes. Musser completed his undergraduate studies in electrical engineering and mathematics at Brown University and his graduate studies in planetary science at Cornell University, where he was a National Science Foundation Graduate Research Fellow. Prior to joining Scientific American, Musser served as editor of Mercury magazine and of The Universe in the Classroom tutorial series for K–12 teachers at the Astronomical Society of the Pacific, a science and science-education nonprofit based in San Francisco. He is also the author of The Complete Idiot's Guide to String Theory. Musser has won numerous awards in his career, including the 2011 American Institute of Physics's Science Writing Award. Follow on Twitter @gmusser

The views expressed are those of the author and are not necessarily those of Scientific American.

Ще намеря и втората част.


Източник: http://blogs.scientificamerican.com/critical-opalescence/how-to-build-your-own-quantum-entanglement-experiment-part-1-of-2/


С две думи - това е лоу кост (максимално евтината) установка за сплетени частици. Лазерите освен, че са скъпи, искат и пълна тъмина и още някои неудобства имат... Статията не е нова де, мисля, че към момента има способ да се правят светодиоди, които излъчват сплетени фотони, не знам дали вече е факт такъв диод.

Тук се използва изотопен бета лъчител - 22Na, оформен като диск и направен така, че от едната ми страна да се излъчват електрони, а от другата позитрони все бета лъчи са това. Детекторите (два гайгерови брояча) ги засичат, но се отчитат само случаитев които има пълно съвпадение - едновременно се очете електрон и позитрон. Интерфейсът е през айпад.


Втората част

How to Build Your Own Quantum Entanglement Experiment, Part 2 (of 2)
By George Musser | February 14, 2013
|
collimated-parallel-cropped.jpgIn my last post, I scrounged the parts for a very crude, but very cool, experiment you can do in your basement to demonstrate quantum entanglement. To my knowledge, it's the cheapest and simplest such experiment ever done. It doesn't give publishable results, but, to appropriate a line from Samuel Johnson, a homebrew entanglement experiment is "like a dog's walking on his hinder legs. It is not done well; but you are surprised to find it done at all." As a warm-up exercise, I sandwich my source of entangled photons--a disk of radioactive sodium-22--between my two Geiger counters (see diagram and photo below) and leave the system to run overnight, measuring how often the Geigers click at the same time. If gamma-ray photons are indeed emerging two by two in opposite directions, the coincidence rate should vary strongly when I change the alignment of the two Geigers. And that is what I see.Directional-coincidences.jpgdirectional.jpgWhen the Geigers are pointing straight at each other, each clicks about 900 times per minute and both do so in unison about 4 times per minute. This is about 40% greater than the expected rate of accidental coincidences. There are various subtleties in separating accidental and genuine coincidence rates and in estimating statistical errors, but the signal I observe is something like 10 standard deviations above the noise. When I rotate one of the Geigers out of alignment, the coincidence rate drops precipitously. For a 25? angle, it only about 15% greater than the accidental rate, which is still statistically significant, if barely. For 45? and 90?, it is equal to the expected accidental rate. So I can tentatively conclude I'm seeing pairs of gammas--one or two of them per minute! This is no mean accomplishment given how crude the equipment is. Just because the gammas emerge in pairs doesn't mean they are entangled, though. To check for entanglement, I measure the photons' polarization with a technique called Compton polarimetry. A pair of aluminum cubes bought atOnlineMetals.com serve as gamma-ray prisms, scattering photons in directions that depend on their polarization. The two gammas produced by the annihilation of an antielectron and electron are linearly polarized at right angles to each other, so they should scatter off the aluminum in perpendicular directions. Here's where the physics gets spooky. Each individual photon scatters in a random direction, yet the random direction one photon takes is related to the random direction its partner does. The gammas act in synchrony. How can they do that, if they're truly random? Einstein concluded that the photons either are not truly random or are acting on each other at a distance. In a first attempt to observe this effect, I sandwich the sodium-22 disk in between the two cubes and put a Geiger on one face of each cube (see photo below). I start by pointing the Geigers in the same direction and letting them sit overnight to count the coincidences. In the morning, I move one Geiger to a different face of its cube, so that the two detectors are now perpendicular to the other, and leave the system to run all day. I continue cycling through different ways to align the detectors either parallel or perpendicular to each other. Entanglement should betray itself as an asymmetry in the coincidence rate.uncollimated-combined.jpgAnd indeed that's what I see. About one coincidence occurs per minute on average, and the rate is consistently greater when the Geigers are perpendicular. It looks like entanglement in action! A wise graduate student would hesitate to show this result to his or her faculty advisor, though. The perpendicular rate stands a couple of standard deviations above the expected accidental-coincidence rate, but the parallel rate swims in the noise. So the asymmetry might well be a fluke of statistics or a subtle bias in the setup. To improve on the experiment, I need to beat down the accidental rate--in particular, the rate caused by gammas traveling straight from the sodium to the Geiger counter rather than scattering off the aluminum. I enclose the radioactive sodium in a so-called collimator: a lead storage canister in which I drilled a 1/2-inch hole at either end. A couple of hundred gammas per minute leak out through each hole, forming a pair of gamma-ray beams. The lead squelches off-axis radiation by a factor of about four.EPR-Apparatus-with-pig.jpgcollimated-combined.jpgWith the collimator, the coincidence rate drops by a factor of 10, but now exceeds the predicted accidental rate for both orientations. The perpendicular rate is the higher of the two, again as the Compton-polarimetry theory predicts for entangled photons. This still isn't anything to call the Nobel committee about. At best, it implies the detection of one entangled pair of photons every 20 minutes, and with such a meager trickle, who knows what subtle bias might be operating. What was iffy for the pioneering Bleuler and Bradt experiment can only be more so for my apparatus. Then again, all I'm seeking is a suggestive demonstration, not a research-grade system. A possible next step would be to special-order a stronger sodium-22 source, which would bring the particle rates in my experiment up to the level of Bleuler and Bradt's, at the price of posing a greater radiation hazard. Another idea would be to try scatterers besides aluminum cubes. Beyond that, however, I think you exhaust the el-cheapo options and have to dig deeper into your wallet, starting with replacing the Geigers counters with scintillation counters, as Wu and Shaknov used. These are more efficient at picking up radiation; create shorter electrical pulses for each particle they detect, which reduces the probability of accidental coincidences; and measure particle energy, which would help to sift out annihilation-produced photons. But such instruments are pricier and fussier. A useful guide to further refinements is Leonard Kaskay's Ph.D. dissertation from 1972. A student of Wu, Kasday systematically went through the possible sources of error: multiple scattering, geometric misalignment, unwanted photons, and more. He was able to achieve enough precision to show that the gammas violated a mathematical inequality derived by theorist John S. Bell, confirming that he was seeing spooky action at a distance rather than some mundane effect. These kinds of experiments are notoriously tricky, so please share your thoughts and advice--not to mention your attempts to reproduce! Wait till your friends hear that you're an amateur quantum physicist in your spare time.
  • George Musser is a contributing editor at Scientific American. He focuses on space science and fundamental physics, ranging from particles to planets to parallel universes. Musser completed his undergraduate studies in electrical engineering and mathematics at Brown University and his graduate studies in planetary science at Cornell University, where he was a National Science Foundation Graduate Research Fellow. Prior to joining Scientific American, Musser served as editor of Mercury magazine and of The Universe in the Classroom tutorial series for K–12 teachers at the Astronomical Society of the Pacific, a science and science-education nonprofit based in San Francisco. He is also the author of The Complete Idiot's Guide to String Theory. Musser has won numerous awards in his career, including the 2011 American Institute of Physics's Science Writing Award. Follow on Twitter @gmusser

The views expressed are those of the author and are not necessarily those of Scientifi

Link to comment
Share on other sites

  • Потребител

Не го разбрах в подробности, но едва ли е открито излъчване на електрони и позитрони едновременно...

Все едно, е направена машина за енергия и то - най-голямата възможна енергия! - от анихилация, в крайност - полеви обекти. (няма частици от "разпад" :grin: при анихилациа на електрон с позитрон )

Гайгерът отчита гама-излъчвания от разпад на радиоактивния материал. Поляризация "нагоре", поляризация "на 90о"... и ако са много - пищи! :harhar: . Като се направи филтър за посока, вероятността за захват намалява и ... не схващам файдата, за изводи... :grin:

...

Link to comment
Share on other sites

  • Модератор Инженерни науки

Добре, Малоум 2, че гледаш и мислиш.

Моя грешка е, че казах че е направен да излъчва електрони от едната страна и позитрони от другата. Истината е, че е гама лъчител с вторично лъчение бета (елетрон или позитрон, в случая е второто) и е направен от едната страна да позволява излъчването на позитрони.

Гайгервият брояч - засича и трите вида лъчение, в зависимост от детектора. Ако е за гама - йонизационната тръба (камера) е пръчка без прозорци, лъчението минава и през единия електрод. Ако е за бета - има прозорче. Ако е за алфа частица (хелиево ядро) - прозорчето е от някаква ципа (полиетилен предполагам), има и голяма площ.

Значи - броим сплетените гама кванти (алфа и бета са частици).

Theory says the entangled gammas in a pair fly off in exactly opposite directions, so I look for them by placing a Geiger on either side of the sample.

"Теорията казва, че двойката сплетени гама кванти излитат от точно противоположни посоки, така че аз ги търся чрез разполагана гайгеровите броячи от двете страни на пробата". Пробата в случая е изотопния диск.

Онова което брои (отчита) съвпаденията е NAND гейт или по български - логически елемент И-НЕ. На схемата е "coincidence box"

Редактирано от Joro-01
Link to comment
Share on other sites

  • Потребител

Радиоактивният натрий се разпада с излъчване на позитрон, неутрино и гама квант. Позитронът анихилира с електрон от околното пространство и се излъчват два слетени гама фотона.

15.jpg
Защо са два - защото фотонът не може да съществува в покой, а законът за запазване на импулса трябва да се спази при процеса на анихилация.

Защо са в противоположни посоки - заради същия закон за запазване на импулса.

Защо са сплетени - защото се получават от един процес.

Link to comment
Share on other sites

  • Модератор Инженерни науки

Не може да няма "+" тук


Ето още на англ.

https://en.wikipedia.org/wiki/Electron%E2%80%93positron_annihilation

Макар, че казаното от Дорис е изчерпателно.

Link to comment
Share on other sites

Напиши мнение

Може да публикувате сега и да се регистрирате по-късно. Ако вече имате акаунт, влезте от ТУК , за да публикувате.

Guest
Напиши ново мнение...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Зареждане...

За нас

Вече 17 години "Форум Наука" е онлайн и поддържа научни, исторически и любопитни дискусии с учени, експерти, любители, учители и ученици.

За своята близо двайсет годишна история "Форум Наука" се утвърди като мост между тези, които знаят и тези, които искат да знаят. Всеки ден тук влизат хиляди, които търсят своя отговор.  Форумът е богат да информация и безкрайни дискусии по различни въпроси.

Подкрепи съществуването на форумa - направи дарение:

Дари

 

 

За контакти:

×
×
  • Create New...