This crystal can split light particles

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There’s a reason that I’m really excited about this random crystal not this one the other ones But this is going to be my metaphor the crystal can entangle photons, [I] made a recent video about a crazy experiment testing quantum entanglement quantum entanglement is like the choose a Gift game of Quantum physics you choose a hand and you automatically know something about the other hand that that’s where the gift was Except that with real, quantum entanglement experiments It’s typically photons that you’re entangling hmM, and you don’t decide where the gift goes beforehand carry on I know this is not the best explanation of quantum entanglement, but I did go into it more in the other video So you can check [that] out if you [want] to focus diana. So how do you make entangled photons? Oh? it turns out creating pairs of entangled photons is a process that Involves Nonlinear crystals and Splitting photons on this optical table. Yeah this whole [set] [up] you have a nonlinear Crystal. That’s right Yeah, the bbo crystal. Where is it? Oh? It’s right inside of that little that little Cylindrical unit in between [that] these [q] green beams here, so it’s like protective. It’s like really hidden It’s really hidden you want to go see it. Yes, let’s go see it, okay That’s inside of a cylinder because you’re trying to keep it as clean as possible So you’ll see there’s actually a tube going in there, and it’s just blowing an obstacle. Oh wow okay, so it doesn’t get And inside of that that that little pedestal as we call it. There is the [bBO] crystal So this is the crystal you need to split photons but wait You can’t actually split photons Because photons are elementary Particles my dear Watson which means that you can’t chop them up into smaller bits and yet beta Barium borate Crystals or [BbO] Crystals as dan was calling them are the common crystals used to take? one photon in at [out] pops [to] because a [b], [bo] Nonlinear Crystal can split photons the incoming photon is absorbed into the crystal and then a process involving vacuum energy fluctuations happens And you can get out two photons But only for every billion or trillion or so Photons that you send in so there are some cool hints about how these crystals work They have to be perfectly grown for each individual experiment plus. There are rules So the energy of the [incoming] photon or photons has to exactly match the total energy [of] the outgoing Photon or photons another rule is that? Momentum needs to be conserved so for a photon coming in straight the photons coming out need to be going off at different Angles just like with colliding pool balls, and the photons can kick back to [Crystal’s] so you’ve got to conserve all that momentum so the Important things for entangling photons are the version of the interactions of the crystal where in goes one photon and out comes to this? process is known as parametric down-conversion the conservation of energy and momentum and Spin is also important because You know the energy and span of momentum of the photons going in so you know the energy has been amended with the photons coming Out [has] to be correlated, and it’s this correlation That’s used to entangle Photons the final process of entanglement involves the direction of polarization of the photons and multiple crystals But I’m not going to get into it in detail So there’s a really great video that does and I’ll put that in the description now Entanglement is not the end of the story Physicists realized they could use nonlinear crystals for all kinds of funds [vans] lab is using crystals to make a you A laser beam, so you’re a theorist, that’s true. Yeah, [I] don’t belong here But you’re doing siri work. Yes work on this experiment in Dan’s lab They take in two photons [and] they get out one they’ve taken two green photons and they get out a UV photon The whole purpose of having the Crystal in [your] optical setup here is to make a UV laser It sounds ridiculous, right? It needs a cold table just to make ultraviolet light like it sounds a little bit ridiculous remember It’s important to be able to tune the frequencies also by the way Dan’s lab uses Uv light [and] Shines it on clouds of plasma for some sweet experiment another interesting use of parametric down-conversion Is this say you want to send a single photon to do something? maybe you want to test if the human eye can sense a single photon [I] talked to a researcher who’s working on this exact question I’m Rebecca Holmes. I’m Well, I was a graduate student at the university of Illinois have just recently graduated So my research was focused on using quantum states of light including single photons to study the human visual system So it turns out your visual system is actually really sensitive you can maybe even see a single photon Where you do think that [bit] [before]? so I what I use it for is I wanted to generate single photons and a good trick for doing that is [to] make two photons at once so you make a photon pair from Spontaneous parametric down conversion and Then you use one photon from the pair you just take that one and send it straight to a single photon detector and count it So when the detector clicks you know that that photon was there so it’s partners there on the other side cool stuff So [that’s] how a [mami] photon becomes to baby photons with the assistance of Nonlinear Crystals and parametric down-conversion Thank you so much for watching this video and happy physics thing. Thanks to [Edx] our non-profit partner for sponsoring this episode Edx.org is where you can learn for free from Harvard mit and other universities around the globe Edx org offers University level courses and everything from artificial intelligence to [robots] and cybersecurity [you] can even earn credits towards a master’s degree or walk away with a professional Certificate to help advance your career my friend Joe over at it’s okay to be smart just made a great video inspired by Harvard Architectural imagination course I recommend checking out circuits and electronics From mit which was called six double o two when I was there and was one of my favorite courses at mit visit Edx org and discover the courses that will keep you learning

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