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<v Speaker 1>Welcome to the quark Side Quantum Physics Podcast, an exploration

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<v Speaker 1>of the fundamental structure of reality where quantum laws govern matter, energy,

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<v Speaker 1>and information. Here, uncertainty is a feature, not a flaw,

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<v Speaker 1>and understanding begins at the smallest scales.

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<v Speaker 2>I want you to imagine, just for a second, a

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<v Speaker 2>world where teleportation isn't you know, some parlor trick or

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<v Speaker 2>a sci fi movie.

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<v Speaker 3>Trope, right, like something out of Star Trek.

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<v Speaker 2>Exactly. Imagine a reality where ultrafast quantum computing and like

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<v Speaker 2>instant fundamentally unhackable information transfer are just the everyday backbone

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<v Speaker 2>of our technology.

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<v Speaker 3>It's wild to think about it, really is.

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<v Speaker 2>You wake up, you log on, and you use a

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<v Speaker 2>global network that shares data with zero lag and perfect security,

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<v Speaker 2>and all of it relies on the strangest, most mind

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<v Speaker 2>bending rules of the universe.

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<v Speaker 3>Yeah, the rules that defy all classical logic.

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<v Speaker 2>Welcome back to the Deep Dive. If you're new here.

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<v Speaker 2>This is the show where we take a massive stack

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<v Speaker 2>of recent research articles, technical papers and we extract the

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<v Speaker 2>absolute most important insights you need to know.

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<v Speaker 3>And today is a big one.

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<v Speaker 2>It is huge. Today our mission is to break down

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<v Speaker 2>a freshly unveiled twenty twenty six scientific breakthrough from researchers

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<v Speaker 2>at Kyoto University and Hiroshima University in Japan.

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<v Speaker 3>Yeah, they've done something incredible.

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<v Speaker 2>They have finally cracked a twenty five year old quantum puzzle,

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<v Speaker 2>and in doing so, they've basically brought next generation quantum

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<v Speaker 2>networks right to our doorstep.

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<v Speaker 3>Okay, let's unpack this because to really grasp how we

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<v Speaker 3>are making this leap from a theoretical dream into hard,

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<v Speaker 3>functual infrastructure, we need to talk about the raw material

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<v Speaker 3>making it all possible.

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<v Speaker 2>Yeah, it really is a profound paradigm shift, because before

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<v Speaker 2>we can dive into how the these Japanese researchers crack

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<v Speaker 2>the code to actually read these complex quantum systems, we

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<v Speaker 2>have to look at how our relationship with quantum entanglement

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<v Speaker 2>has completely evolved. Right now, we know you listeners follow

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<v Speaker 2>this space, so we aren't gonna bore you with the

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<v Speaker 2>whole Shrewdinger's cat thing or basic particle physics one oh one.

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<v Speaker 2>You already know what entanglement is, right, the.

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<v Speaker 3>Idea that subatomic particles like photons can become so deeply

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<v Speaker 3>linked that their properties just can't be understood individually anymore, exactly.

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<v Speaker 3>Try have to treat the whole system as a unified

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<v Speaker 3>reality exactly. But what's vital to understand here is the

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<v Speaker 3>philosophical shift. In the scientific community. For decades, entanglement was

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<v Speaker 3>viewed mostly as a headache.

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<v Speaker 2>We're really complicated headache.

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<v Speaker 3>Yeah. It famously troubled Albert Einstein. He called it spooky

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<v Speaker 3>action at a distance because it seemed to completely violate

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<v Speaker 3>the classical rules of reality.

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<v Speaker 2>Right, it broke all's rules.

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<v Speaker 3>It was a curiosity, a puzzle to be observed. But

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<v Speaker 3>today it is the actual tangible raw material for a

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<v Speaker 3>new industrial revolution. It is like the clay we're trying

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<v Speaker 3>to mold.

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<v Speaker 2>Which is still incredibly spooky when you think about it.

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<v Speaker 2>I mean, even if we accept it as raw material,

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<v Speaker 2>it defies everyday logic.

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<v Speaker 3>Oh absolutely.

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<v Speaker 2>Imagine you have a pair of magic dice. If you

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<v Speaker 2>roll one of those dice in New York and it

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<v Speaker 2>lands on a six, the entangled die sitting in a

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<v Speaker 2>server room in Tokyo instantly rolls a six, no matter

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<v Speaker 2>the distance between them, instantaneously, right, no wires, no physical signals,

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<v Speaker 2>just an instant link. But wait, if it's just spooky action,

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<v Speaker 2>How do we actually use it to build a computer?

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<v Speaker 2>How do you take that magic trick and turn it

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<v Speaker 2>into a reliable machine.

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<v Speaker 3>This raises an important question because it gets to the

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<v Speaker 3>very heart of the engineering bottleneck. Okay, in a classical computer,

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<v Speaker 3>your infrastructure is built on transistors reading physical states as

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<v Speaker 3>simple ones or.

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<v Speaker 2>Zeros, right, standard binary exactly.

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<v Speaker 3>But in a quantum computer, you are using the entangled

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<v Speaker 3>state itself to perform calculations and route information.

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<v Speaker 2>Wow.

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<v Speaker 3>Okay, yeah. By treating a system of entangled particles as

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<v Speaker 3>a unified whole, any manipulation of the system inherently processes

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<v Speaker 3>vast amounts of data simultaneously.

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<v Speaker 2>So it's exponentially faster.

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<v Speaker 3>Right. So creating the entanglement is step one. But the

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<v Speaker 3>real challenge, the thing that has held up the quantum

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<v Speaker 3>Internet for decades, is step two, which is what figuring

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<v Speaker 3>out how to measure or read that entanglement without destroying

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<v Speaker 3>its usefulness.

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<v Speaker 2>Ah. I see. So if entanglement is our magic clay,

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<v Speaker 2>it's not enough to just mash the clay together. If

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<v Speaker 2>you actually want to process information, you have to be

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<v Speaker 2>able to look at the clay and know exactly what

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<v Speaker 2>shape it to.

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<v Speaker 3>Me precisely creating entangled states in a laboratory is something

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<v Speaker 3>physicists have actually gotten quite good at. Oh really, Yeah,

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<v Speaker 3>but just throwing photons together isn't enough. You have to

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<v Speaker 3>reliably verify what kind of entangled state you have created,

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<v Speaker 3>purely and accurately, right.

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<v Speaker 2>You need to know what you made exactly.

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<v Speaker 3>And for years, the standard method for doing this was

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<v Speaker 3>something called quantum tomography.

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<v Speaker 2>Tomography like a CT scam in a hospital.

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<v Speaker 3>Similar concept, yeah, but infinitely more frustrating. At the quantum level.

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<v Speaker 3>Quantum tomography tries to estimate a quantum state by taking

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<v Speaker 3>thousands upon thousands of measurements of identical copies of that state.

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<v Speaker 2>That sounds exhausting, it is.

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<v Speaker 3>It's basically a statistical guessing game, and it has a

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<v Speaker 3>fatal mathematical flaw. As you add more photons to the system,

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<v Speaker 3>the number of measurements you need to take grows explosively.

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<v Speaker 3>It scales exponentially.

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<v Speaker 2>Wow. So, if I'm trying to build a fast network,

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<v Speaker 2>quantum demography is basically like trying to figure out a

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<v Speaker 2>wedding kick's exact recipe by tasting it one microscopic crumb

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<v Speaker 2>at a time. Yeah, Like, Okay, this crumbhusbandilla, let me

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<v Speaker 2>test the next crumb. It takes forever, and by the

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<v Speaker 2>time you've mapped the whole cake, the data is useless.

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<v Speaker 2>You've completely bogged down the network.

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<v Speaker 3>That is a perfect way to visualize it. You are

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<v Speaker 3>destroying the system crumb by crumb to guess the recipe.

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<v Speaker 2>So what's the alternative.

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<v Speaker 3>The solution to this massive bottleneck is something called an

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<v Speaker 3>entangled measurement.

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<v Speaker 2>Okay.

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<v Speaker 3>Instead of looking at into visual crumbs, an entangled measurement

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<v Speaker 3>allows scientists to identify a specific complex entangled state in

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<v Speaker 3>a single shot. You measure the whole cake at once.

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<v Speaker 2>Which sounds way more efficient.

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<v Speaker 3>It is, and scientists had already proven this single shot

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<v Speaker 3>method was possible for one specific type of entanglement known

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<v Speaker 3>as the GHz state GC. Yeah, named after the physicists Greenberger,

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<v Speaker 3>Horn and Xylander.

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<v Speaker 2>Okay, got it.

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<v Speaker 3>But there is another vastly more important type of multiphoton

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<v Speaker 3>entanglement called the W state, And for twenty five years,

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<v Speaker 3>a single shot measurement for the W state remained entirely

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<v Speaker 3>out of reach, completely impossible.

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<v Speaker 2>Okay, I have to ask why was this WO state

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<v Speaker 2>so uniquely difficult? What makes it different from the GHz state.

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<v Speaker 3>What's fascinating here is the mechanics of how the entanglement

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<v Speaker 3>is distributed. Think of the GHD state like a very

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<v Speaker 3>rigid house of cars. If you measure one photon, it

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<v Speaker 3>immediately determines the state of the others in a very strict,

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<v Speaker 3>predictable way. But because it's so rigid, it's also incredibly fragile.

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<v Speaker 2>Like blowing on a house of cards.

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<v Speaker 3>Exactly, if you lose a single photon to environmental noise,

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<v Speaker 3>the entire entangled system collapses. The W state, though, is

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<v Speaker 3>entirely different. It is characterized by a shared distributed.

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<v Speaker 2>Entanglement distributed how the.

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<v Speaker 3>Quantum information is smeared delicately across all the photons.

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<v Speaker 2>Oh wow, so it's less like a house of cards

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<v Speaker 2>and more like, uh, a safety net.

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<v Speaker 3>Exactly, if you lose a photon in a W state,

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<v Speaker 3>the remaining photons actually stay entangled.

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<v Speaker 2>That's amazing.

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<v Speaker 3>It is incredibly robust against noise and particle loss, which

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<v Speaker 3>is exactly why it is the holy grail for real

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<v Speaker 3>world quantum networks.

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<v Speaker 2>Right because the real world is messy, Right, You.

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<v Speaker 3>Want that durability. If you're sending data under city streets.

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<v Speaker 3>But that very same distributed smeared nature made it agonizingly

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<v Speaker 3>difficult to mathematically design a measurement that could identify it

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<v Speaker 3>in a single shot.

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<v Speaker 2>Here's where it gets really interesting, because Shigeki ta Kuchi

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<v Speaker 2>and the university teams in Japan didn't just try to

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<v Speaker 2>smash these W states with brute force.

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<v Speaker 3>No they didn't.

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<v Speaker 2>According to the research, they found a structural workaround. They

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<v Speaker 2>successfully performed a single shot entangled measurement identifying the W

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<v Speaker 2>state using three photons.

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<v Speaker 3>Yeah, a massively.

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<v Speaker 2>And they did it by looking for something called cyclic

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<v Speaker 2>shift symmetry. Let me try to wrap my head around

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<v Speaker 2>that is cyclic shifts symmetry kind of like a musical chord.

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<v Speaker 3>A musical chord.

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<v Speaker 2>Yeah, Like think of a C major chord on a

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<v Speaker 2>piano c eng If you move the seed to the

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<v Speaker 2>top so it's EGC, it's still fundamentally a C major chord.

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<v Speaker 2>It's an inversion.

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<v Speaker 3>Oh, I see where you're going, right.

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<v Speaker 2>No matter how you cycle or shift those specific notes around,

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<v Speaker 2>the underlying harmony stays perfectly recognizable.

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<v Speaker 3>That is a brilliant analogy. Yes, even as the specific

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<v Speaker 3>configurations of the photons shift within the system. There is

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<v Speaker 3>a fundamental symmetrical property, a underlying harmon that defines the

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<v Speaker 3>entire system as a W state.

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<v Speaker 2>Okay, so how do they actually measure that?

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<v Speaker 3>To actually detect this cord, the Japanese researchers designed a

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<v Speaker 3>highly specialized photonic quantum circuit.

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<v Speaker 2>Built out of light.

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<v Speaker 3>Built out of light, This circuit performs something called a

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<v Speaker 3>quantum fourya transformation, specifically tailored for W states.

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<v Speaker 2>A four EA transform. I know that's used in audio

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<v Speaker 2>engineering to break down complex sound waves into individual frequencies.

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<v Speaker 2>How does a quantum circuit do that to light?

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<v Speaker 3>Well, In a traditional computer, a Fouria transform is a

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<v Speaker 3>really heavy mathematical calculation. But in this photonic circuit, the

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<v Speaker 3>math is done physically by the light itself.

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<v Speaker 2>Wait, physically yeah.

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<v Speaker 3>The circuit uses an intricate web of beam splitters and

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<v Speaker 3>phase shifters. As the entangled photons travel through these paths,

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<v Speaker 3>their light waves naturally interfere with each other.

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<v Speaker 2>Oh wow.

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<v Speaker 3>This physical interference acts as the calculation, taking that hidden

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<v Speaker 3>shifting symmetry of the W state and naturally amplifying it

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<v Speaker 3>into a clear, measurable signal at the output.

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<v Speaker 2>That is wild.

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<v Speaker 3>They literally built an optical machine that naturally filters for

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<v Speaker 3>that specific quantum harmony.

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<v Speaker 2>That is incredible. But you know, the paper also notes

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<v Speaker 2>that they fed three single photons into this device, and

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<v Speaker 2>they were looking at the fidelity of the results, right,

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<v Speaker 2>fidelity fidelity being the probability that the device gives the

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<v Speaker 2>right result when it's fed a pure W state. Does

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<v Speaker 2>this mean the machine still makes mistakes? I mean, if

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<v Speaker 2>we are building an ultra secure Internet of the future,

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<v Speaker 2>we can't have a router that just drops packets or

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<v Speaker 2>misreads data because of probability error.

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<v Speaker 3>Right, it's very valid concern, But in quantum mechanics, fidelity

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<v Speaker 3>doesn't mean the machine is glitching or making a software error.

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<v Speaker 2>Okay, so what does it mean.

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<v Speaker 3>It's a measure of absolute precision against microscopic environmental noise.

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<v Speaker 3>No physical system is ever one hundred percent perfect, but

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<v Speaker 3>achieving a highly elevated fidelity means the fundamental mechanism is

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<v Speaker 3>definitively proven.

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<v Speaker 2>So it works.

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<v Speaker 3>It works, But honestly, the fidelity isn't even the most

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<v Speaker 3>groundbreaking part of the device. The real game changer is

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<v Speaker 3>its stability. This entire optical circuit is passive.

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<v Speaker 2>Wait passive that defies everything I know about quantum labs.

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<v Speaker 2>Usually you see these giant gold, steampunk chandeliers hanging inside

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<v Speaker 2>deep freeze vacuum chambers.

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<v Speaker 3>Oh yeah, the dilution refrigerators, right, and.

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<v Speaker 2>They require a whole team of postdocs constantly tweaking lasers

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<v Speaker 2>just to keep the experiment alive for like a millisecond exactly.

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<v Speaker 3>Traditional quantum setups are agonizingly fragile, but this team built

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<v Speaker 3>a device out of light that ran for an extended

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<v Speaker 3>period without any active real time control or continuous calibration.

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<v Speaker 2>It just ran on its own.

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<v Speaker 3>They remain highly stable on its own. Yeah, And proving

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<v Speaker 3>that we can achieve high fidelity readings on a stable

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<v Speaker 3>passive device is the turning point. It proves we don't

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<v Speaker 3>need a perfectly pristine, constantly adjusted, million dollar laboratory to read.

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<v Speaker 2>These networks, which means we can actually take the technology outside.

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<v Speaker 2>We can out of the lab and start bolting it

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<v Speaker 2>into actual city infrastructure.

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<v Speaker 3>Exactly, we can put it in the real world.

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<v Speaker 2>And that transition into the real world brings us to

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<v Speaker 2>the actual teleportation networks. Just to be absolutely clear for

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<v Speaker 2>everyone listening, we are talking about beaming data instantaneously, not

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<v Speaker 2>beaming humans like on Star Trek, right, right.

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<v Speaker 3>It is vital to be precise with the terminology. Quantum

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<v Speaker 3>teleportation is the transfer of quantum information from one location

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<v Speaker 3>to another without physically moving any matter through the space

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<v Speaker 3>between them.

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<v Speaker 2>So we aren't mailing a photon.

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<v Speaker 3>No, you aren't sending a photon in a microscopic FedEx

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<v Speaker 3>box from point A to point B. You are utilizing

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<v Speaker 3>that entangled link we talked about at the beginning to

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<v Speaker 3>instantly transfer the exact quantum state of a particle in

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<v Speaker 3>location A onto a completely different waiting particle in location B.

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<v Speaker 2>And what blows my mind is the timeline of how

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<v Speaker 2>fast this is moving. The source of show that in

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<v Speaker 2>late twenty twenty five researchers achieved all photonic quantum teleportation

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<v Speaker 2>in a hybrid urban network. Yes, a major milestone, and

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<v Speaker 2>they did it using something called quantum dots. What exactly

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<v Speaker 2>is a quantum dot doing in a city network?

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<v Speaker 3>A quantum dot is essentially a tiny nanoscale semiconductor crystal.

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<v Speaker 3>You can think of them as artificial atoms. Artificial atoms, yeah,

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<v Speaker 3>because of their size, they trap electrons in a way

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<v Speaker 3>that allows them to emit single photons on demand. Very predictably.

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<v Speaker 2>Oh, I see, in a.

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<v Speaker 3>Hybrid urban network, you need a reliable, high quality source

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<v Speaker 3>of single photons to carry the quantum information, and quantum

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<v Speaker 3>dots act as those perfect little photon factories interfacing between

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<v Speaker 3>different types of quantum hardware across the city.

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<v Speaker 2>So they are generating the data carriers. And the pace

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<v Speaker 2>of this is just staggering, because right after that urban

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<v Speaker 2>network test in twenty twenty five, twenty twenty six saw

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<v Speaker 2>another massive leap.

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<v Speaker 3>It really did.

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<v Speaker 2>The reports show a completely different team built an integrated

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<v Speaker 2>photonic chip capable of manipulating and measuring complex multipart entanglement

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<v Speaker 2>all on a single tiny device.

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<v Speaker 3>Incredible miniaturization right.

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<v Speaker 2>And perhaps most impressively, also in twenty twenty six, researchers

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<v Speaker 2>tested a three node quantum network right across existing standard

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<v Speaker 2>fiber optic cables in New York.

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<v Speaker 3>City using standard cables.

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<v Speaker 2>Yeah, they did this using a process called entanglement swapping.

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<v Speaker 2>How exactly do you swap entanglement under the streets of Manhattan.

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<v Speaker 3>Entanglement swapping is essentially a quantum relay race. Imagine you

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<v Speaker 3>have three nodes in the network, Alice, Bob and Charlie Okay,

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<v Speaker 3>Alice and Bob are far apart and have never interacted,

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<v Speaker 3>but they both share an entangled link with Charlie, who

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<v Speaker 3>is sitting in the middle.

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<v Speaker 2>So Charlie is the hub.

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<v Speaker 3>Right, Charlie performs a specific entangled measurement on his particles.

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<v Speaker 3>Because of the rules of quantum mechanics, the very act

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<v Speaker 3>of Charlie taking that measurement instantly causes Alice and Bob's

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<v Speaker 3>particles to become entangled with each other, even though they've

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<v Speaker 3>never met.

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<v Speaker 2>Wait, really that fast.

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<v Speaker 3>Instantly, Charlie just swapped the entanglement to them. This is

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<v Speaker 3>how you route a quantum connection over long distances, bouncing

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<v Speaker 3>it from node to node through the messy temper fluctuating

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<v Speaker 3>fiber cables under New York.

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<v Speaker 2>And if we connect the dots here, the Japanese team's

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<v Speaker 2>W state breakthrough is the ultimate missing piece for that

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<v Speaker 2>relay race. You can have the fiber cables, you can

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<v Speaker 2>use entanglement swapping to rout the signal, and you can

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<v Speaker 2>use quantum dots to generate the photons. But to make

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<v Speaker 2>it work at scale without lagging, you need to be

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<v Speaker 2>able to verify that the robust W state information actually

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<v Speaker 2>arrived correctly yes, you need an ultrafast single shot scanner.

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<v Speaker 2>Without this new Kyoto and Hiroshima circuit, the New York

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<v Speaker 2>network would just get bogged down trying to read the

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<v Speaker 2>cake crumb by chrome.

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<v Speaker 3>If we connect this to the bigger picture, yes, they

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<v Speaker 3>have provided the high speed optical scanner for the future Internet,

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<v Speaker 3>and they were already planning their next moves.

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<v Speaker 2>Oh, what's next.

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<v Speaker 3>The researchers intend to extend this passive method to larger

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<v Speaker 3>multiphoton states, well beyond just three photons, and they're actively

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<v Speaker 3>working to develop on ship photonic circuits to make it

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<v Speaker 3>even small. They want to make the process of reading

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<v Speaker 3>these states faster, smaller, and vastly more practical for mass production.

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<v Speaker 3>They are literally laying the bricks for a fundamentally unhackable Internet.

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<v Speaker 2>Completely unhackable because.

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<v Speaker 3>In a quantum network, information cannot be intercepted or copied

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<v Speaker 3>by a hacker without instantly destroying the state and alerting

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<v Speaker 3>the sender. It represents the absolute pinnacle of data security.

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<v Speaker 2>So what does this all mean. Let's pull all these

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<v Speaker 2>threads together. We started with the basic reality of quantum entanglement,

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<v Speaker 2>a concept so bizarre that it made Einstein's headspin.

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<v Speaker 3>It definitely did.

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<v Speaker 2>For decades. Even as we learned to create that spooky

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<v Speaker 2>action in pristine labs, we were stuck at a massive

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<v Speaker 2>engineering bottleneck. We could make the magic clay, but we

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<v Speaker 2>couldn't read it efficiently because quantum tomography was just too

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<v Speaker 2>slow and destructive, way too slow. Then this massive twenty

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<v Speaker 2>twenty six breakthrough happens. Researchers in Japan finally figure out

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<v Speaker 2>how to instantly read the highly complex durable W state.

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<v Speaker 3>In a single shot, such a huge deal.

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<v Speaker 2>They use cyclic shift symmetry to physically listen for the

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<v Speaker 2>underlying musical cord of the photons using a completely passive

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<v Speaker 2>light based circuit. And this is all happening concurrently with

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<v Speaker 2>massive real world strides miniaturized quantum chips, single photon quantum dots,

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<v Speaker 2>and actual teleportation networks swapping entanglement through the dirty fiber

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<v Speaker 2>optic cables under New York City.

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<v Speaker 3>It's all coming together at once, it really is.

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<v Speaker 2>I really want you the listener, to think about how

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<v Speaker 2>this transforms the reality you interact with every day. We

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<v Speaker 2>are moving away from fragile science experiments and toward actual

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<v Speaker 2>durable chips that will power the communication networks you will

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<v Speaker 2>use in the near future. The quantum Internet isn't one

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<v Speaker 2>hundred years away, It's actively being built right beneath our feet.

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<v Speaker 3>It truly is the dawn of a new era of infrastructure,

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<v Speaker 3>and as we transition from struggling to read just three

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<v Speaker 3>entangled photons to eventually networking billions of them across global

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<v Speaker 3>fiber optics, it forces us to ask a profound question,

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<v Speaker 3>what happens to our traditional concepts of distance, time, and security.

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<v Speaker 3>If massive amounts of information can be shared instantly and

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<v Speaker 3>intrinsically across the globe without ever physically traveling the space

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<v Speaker 3>between two points, are we on the verge of building

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<v Speaker 3>a world where distance simply ceases to exist. Wow, just

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<v Speaker 3>like the teleportation we imagined at the very beginning. We

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<v Speaker 3>might not be beaming humanity through space, but we are

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<v Speaker 3>absolutely beaming reality.