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Breakthrough Quantum Material Conducts Electricity With Zero Energy Loss · The Quark Side - Quantum Physics Podcast

0:01
Speaker 1: Welcome to the quart Side Quantum Physics Podcast, an exploration
0:05
Speaker 1: of the fundamental structure of reality, where quantum laws govern matter, energy,
0:11
Speaker 1: and information. Here, uncertainty is a feature, not a flaw,
0:16
Speaker 1: and understanding begins at the smallest scales.
0:27
Speaker 2: Hello everyone, and welcome back. It is Thursday, February twelfth,
0:31
Speaker 2: twenty twenty six. I want to start today's exploration with
0:36
Speaker 2: a feeling, a sensation that I guarantee every single one
0:39
Speaker 2: of you has felt. It's that very specific kind of annoyance.
0:43
Speaker 2: You're sitting there, maybe you're on a long video call,
0:45
Speaker 2: or you're rendering a video, or maybe you're just you know,
0:48
Speaker 2: scrolling on your phone with the brightness all the way up,
0:51
Speaker 2: and then you feel it, the heat, the heat. Your
0:54
Speaker 2: phone starts to feel like a hot little brick. Your
0:57
Speaker 2: laptop fan suddenly kicks in, and it's like a tiny
1:01
Speaker 2: jet engine is about to take off from your desk.
1:03
Speaker 3: And your battery percentage just plummets.
1:05
Speaker 2: It's just nose dives. Yeah, and we treat this as normal.
1:07
Speaker 2: We just think, oh, my device is working hard. But
1:10
Speaker 2: when you really stop and think about the physics of it, yeah,
1:13
Speaker 2: that heat is just failure, isn't it.
1:15
Speaker 3: It's pure failure. It is waste. In physics, we call
1:18
Speaker 3: it dissipation. And it is, without a doubt, the single
1:21
Speaker 3: biggest bottleneck in modern electronics.
1:23
Speaker 2: So that heat is just energy that's not doing what
1:25
Speaker 2: I wanted to do exactly.
1:27
Speaker 3: That heat is literally your batteries, precious energy being turned
1:31
Speaker 3: into useless themal vibration. Instead of you know, running the
1:34
Speaker 3: app you just opened, it's just gone.
1:36
Speaker 2: It's like paying for a gallon of gas and just
1:37
Speaker 2: pour and have it in the ground before you even
1:39
Speaker 2: start the car. So the reason we're talking about this,
1:42
Speaker 2: this very fundamental problem, is because of a paper that
1:45
Speaker 2: just dropped, I mean just dropped two days ago February tenth,
1:48
Speaker 2: twenty twenty six in the journal Nature Physics. It's from
1:52
Speaker 2: a team at the University of Washington led by researcher
1:55
Speaker 2: name Shaodong Shoo.
1:56
Speaker 3: And it is a monster of a paper, truly, it
1:59
Speaker 3: really is.
2:00
Speaker 2: Because they are claiming to have well essentially solved the
2:04
Speaker 2: heat problem. Yeah, and not in some small incremental we
2:08
Speaker 2: made the copper wiring slightly better kind of way.
2:11
Speaker 3: So this is a fundamental shift.
2:13
Speaker 2: They have engineered a material where electricity flows with zero
2:16
Speaker 2: heat loss.
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Speaker 3: Effectively zero no dissipation. It is the first practical, verified
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Speaker 3: realization of what's called a dissipationless fractional churn insulator.
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Speaker 2: Okay, dissipationless fractional churn insulator. That's a mouthful. I feel
2:33
Speaker 2: like we need to put a giant pin in that
2:34
Speaker 2: phrase because there is a lot of physics jargon packed
2:37
Speaker 2: into those forwards. There is will unpack it all you will,
2:41
Speaker 2: but the headline, the big takeaway here is that they
2:44
Speaker 2: have created a state of matter where electrons just flow
2:48
Speaker 2: without resistance. And this is the kicker. They've done it
2:52
Speaker 2: without the massive, room sized magnetic fields that you usually
2:56
Speaker 2: need for this kind of quantum magic, and.
2:59
Speaker 3: That is the holy part of this. We've known about
3:01
Speaker 3: zero resistance states for a long time, but they always
3:04
Speaker 3: always required these insane lab conditions that made them totally
3:08
Speaker 3: impractical for say a microchip. Right this paper, it completely
3:12
Speaker 3: changes the playing field.
3:13
Speaker 2: So here's our roadmap for this analysis. Yeah, first we
3:16
Speaker 2: have to start with the physics of the impossible. You know,
3:18
Speaker 2: how do you even get electrons to stop bumping into things?
3:21
Speaker 2: We need to talk about this whole family of quantum hall.
3:23
Speaker 3: Effects, right, the basics.
3:25
Speaker 2: Then we need to get into the drama of the engineering,
3:28
Speaker 2: because this isn't the first time this team has tried this.
3:31
Speaker 2: They actually took a swing at it back in twenty
3:32
Speaker 2: twenty three and it didn't quite work.
3:35
Speaker 3: It was a fascinating failure, though, one of those successful
3:38
Speaker 3: failures that pushes science forward exactly.
3:41
Speaker 2: So we'll talk about what went wrong then and the
3:44
Speaker 2: incredibly specific, almost artisanal changes they made to the crystal
3:50
Speaker 2: growth and this twisting mechanism to finally make it work
3:54
Speaker 2: this year.
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Speaker 3: And then there's the mystery.
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Speaker 2: Yes, we have to talk about the mystery, because there's
3:58
Speaker 2: a section at the end of this paper that base
4:00
Speaker 2: sickly says, Okay, we built it. It works perfectly, but
4:02
Speaker 2: now it's behaving in a way that makes absolutely no
4:04
Speaker 2: sense to us.
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Speaker 3: The thermal activation gap mystery. It's a genuine plot twist
4:08
Speaker 3: in the data.
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Speaker 2: So let's dive in section one, the physics of the impossible.
4:12
Speaker 2: I want you to explain resistance to me, like I'm well,
4:16
Speaker 2: let's say a smart high school student, Why does my
4:19
Speaker 2: fane get hot? What is actually happening at the atomic level?
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Speaker 3: Okay? Sure, To really get resistance, you have to visualize
4:25
Speaker 3: the life of a single electron trying to get through
4:28
Speaker 3: a wire. We have this mental picture of electricity as
4:32
Speaker 3: like water flowing smoothly through a pipe, a.
4:34
Speaker 2: Nice, clean, continuous stream, right.
4:36
Speaker 3: But at the atomic level, a copper wire is a
4:39
Speaker 3: complete nightmare. It is a chaotic, crowded, messy obstacle course.
4:44
Speaker 2: So the electron isn't just gliding along, not.
4:47
Speaker 3: At all, not even close. Imagine you're on a highway,
4:49
Speaker 3: but this highway has no lanes, no speed limit, and
4:51
Speaker 3: it's just filled with giant, vibrating boulders. The boulders are
4:55
Speaker 3: the atoms of the copper and the highway is also
4:57
Speaker 3: full of other cars, which are all the other electrons.
5:00
Speaker 3: The electron hits the gas that's the voltage you apply,
5:03
Speaker 3: and it zooms forward, but almost immediately whack it smacks
5:08
Speaker 3: into an impurity in the metal. It recovers, zooms again, Whack,
5:12
Speaker 3: it hits an atom that's just vibrating because of temperature.
5:15
Speaker 3: It recovers again, whack, it collides with another electron.
5:18
Speaker 2: In every single one of those collisions, that's the heat.
5:21
Speaker 3: That is the heat precisely in physics we call it scattering.
5:25
Speaker 3: The electron has kinetic energy, energy of motion. When it
5:28
Speaker 3: crashes into an atom, it transfers some of that energy,
5:31
Speaker 3: making the atom vibrate even more violently. That collective violent
5:35
Speaker 3: vibration of all the atoms is what we feel and
5:38
Speaker 3: measure as heat. So resistance is really just a measure
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Speaker 3: of how often your electrons are crashing.
5:43
Speaker 2: It's friction, It's electrical friction.
5:45
Speaker 3: It is the exact same principle. Now, for decades, physicists
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Speaker 3: have been absolutely obsessed with one question, how do we
5:52
Speaker 3: stop the crashing? How can we build a highway where
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Speaker 3: it's physically impossible for the electrons to hit anything?
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Speaker 2: Which sounds well impossible, and that brings us to the
6:01
Speaker 2: quantum hall effect. Okay, I've heard this term thrown around
6:04
Speaker 2: usually when people are talking about Nobel prizes, but what
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Speaker 2: is it actually?
6:07
Speaker 3: Okay, so let's take that chaotic highway, your normal copper wire.
6:12
Speaker 3: The first thing we do is we cool it way
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Speaker 3: way down to near absolute zero, so.
6:17
Speaker 2: Like a few degrees above the coldest possible temperature in.
6:20
Speaker 3: The universe exactly. That slows down the vibrating atoms. It's
6:24
Speaker 3: like clearing most of the boulders off the road. The
6:26
Speaker 3: road is now much smoother, Okay.
6:28
Speaker 2: Smooth road. But the electrons the other cars are still there.
6:32
Speaker 2: They can still crash into each other.
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Speaker 3: They can. So next we turn on a magnet, and
6:37
Speaker 3: not just any magnet, a massive magnet. We're talking about
6:40
Speaker 3: magnetic fields of ten, maybe twenty tesla. These are monsters.
6:46
Speaker 2: Just for context, a hospital MRI machine is what one
6:49
Speaker 2: point five or maybe three tesla.
6:51
Speaker 3: Right, So we were talking about fields that would rip
6:54
Speaker 3: a metal chair across the room. It's an incredibly strong field. Now,
6:58
Speaker 3: when you apply that kind of magnetic force perpendicular to
7:01
Speaker 3: an electron's motion, the electrons path curves.
7:05
Speaker 2: It doesn't go straight anymore, it can't.
7:06
Speaker 3: The field forces it to move in a circle. This
7:09
Speaker 3: is a fundamental principle called cyclotron motion.
7:11
Speaker 2: So now instead of all the cars driving straight down
7:13
Speaker 2: the highway, they're all just driving in tiny little circles
7:15
Speaker 2: in place that doesn't seem very useful.
7:17
Speaker 3: In the middle of the material, what we call the bulk, yes,
7:20
Speaker 3: they're just spinning in pla is completely trapped going nowhere.
7:22
Speaker 3: But think about what happens at the very edge of
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Speaker 3: the material. Think about the guard rail on the side
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Speaker 3: of the highway.
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Speaker 2: Okay, so I'm an electron near the edge. I try
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Speaker 2: to spin in a circle to my right, but before
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Speaker 2: I can complete the circle, I hit the wall.
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Speaker 3: You hit the wall, so you bounce off it. You
7:40
Speaker 3: try to spin again, You hit the wall again, You
7:42
Speaker 3: bounce again. What ends up happening is this beautiful skipping motion.
7:48
Speaker 3: The electrons skip jump along the boundary of the material.
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Speaker 2: Okay, I can picture that.
7:53
Speaker 3: And here is the magic part. Because the magnetic field
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Speaker 3: forces everything to try and turn, let's say to the right,
8:00
Speaker 3: all the electrons on that one edge are forced to
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Speaker 3: move in exactly the same direction.
8:04
Speaker 2: It creates a one way street.
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Speaker 3: A perfect one way dissipationless super highway. There's no oncoming traffic.
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Speaker 3: An electron can't scatter backwards because to do that, it
8:14
Speaker 3: would have to turn left, and the magnetic field makes
8:16
Speaker 3: that physically impossible.
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Speaker 2: So it literally can't crash.
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Speaker 3: It can't. And this is what we call a topological
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Speaker 3: property topology.
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Speaker 2: That's the branch of math about shapes. Right, the whole
8:26
Speaker 2: donut and coffee mug thing exactly.
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Speaker 3: In topology, a coffee mug and a doughnut are considered
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Speaker 3: the same because they both have one hole. You can
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Speaker 3: squish and stretch one into the other. Without tearing it.
8:37
Speaker 3: In the quantum Hall effect, the flow of electrons along
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Speaker 3: the edge is protected by the topology of the system's
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Speaker 3: quantum state.
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Speaker 2: So even if there's a bump, like a defect in
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Speaker 2: the material.
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Speaker 3: The electron just flows smoothly around it. It can't scatter backwards.
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Speaker 3: It's robust. The resistance along that edge just vanishes. It
8:56
Speaker 3: goes to zero.
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Speaker 2: Wow.
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Speaker 3: And when you measure it, the Hall resistance doesn't increase smoothly.
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Speaker 3: It goes up in these perfect quantized steps, like a staircase,
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Speaker 3: step one, step two. It's this beautiful, perfect order emerging
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Speaker 3: from total chaos.
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Speaker 2: Okay, so that's the quantum Hall effect that the paper
9:13
Speaker 2: we're discussing today. It's not just about that. It's about
9:15
Speaker 2: the fractional quantum Hall effect. And this is where my
9:18
Speaker 2: brain starts to hurt a little bit. How can you
9:20
Speaker 2: have a fraction of a step? How on Earth can
9:22
Speaker 2: you have a fraction of an electron?
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Speaker 3: This is one of the coolest, most mind bending concepts
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Speaker 3: in all of physics. And you're right. An electron is
9:30
Speaker 3: a fundamental particle. It's an elementary particle. You can't take
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Speaker 3: a tiny knife and slice it into thirds, right, but
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Speaker 3: you can get a group of electrons to act collectively
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Speaker 3: as if they are fractional particles.
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Speaker 2: Okay, explain that what does that even mean?
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Speaker 3: It all comes down to collective behavior. Think about it
9:47
Speaker 3: like this. Imagine you're in a crowded room. If everyone
9:51
Speaker 3: is just milling about randomly, you just have a collection
9:53
Speaker 3: of individuals. But what if everyone links arms and starts
9:57
Speaker 3: moving together in a very specific, comp plex braided dance.
10:01
Speaker 2: Then the crowd itself becomes a thing. The entity is
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Speaker 2: the pattern of the dance, not the individual person.
10:07
Speaker 3: That's a perfect way to put it. In the fractional
10:09
Speaker 3: quantum Hall effect or FQHG, the conditions are so extreme,
10:13
Speaker 3: the magnetic field is even stronger, the material is even cleaner,
10:17
Speaker 3: that the electrons can't ignore each other anymore. Their mutual
10:20
Speaker 3: repulsion becomes the dominant force. There's force to interact intensely.
10:25
Speaker 3: They organize themselves into this incredibly delicate correlated quantum liquid.
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Speaker 2: A liquid made of electrons, a.
10:32
Speaker 3: Quantum liquid, yes, And the tiny ripples in this liquid,
10:36
Speaker 3: the little vortices or excitations they behave mathematically exactly like
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Speaker 3: particles with a fractional charge, like one third of an electrons.
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Speaker 2: Chart or two thirds, so we're not splitting the particle.
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Speaker 2: We are creating a quasi particle out of the collective
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Speaker 2: dance of the crowd.
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Speaker 3: You've nailed it. That's the can reuse. These are quasi particles.
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Speaker 3: They're often called enians, and they are incredibly important for
11:02
Speaker 3: the future of technology. Why because they're stable, because they're topological.
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Speaker 3: They're born out of this global collective dance, which makes
11:08
Speaker 3: them super robust. If you poke one individual electron, the
11:13
Speaker 3: overall dance just continues. The fractional quasi particle remains intact.
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Speaker 2: And this is the link to quantum computing, right, This
11:20
Speaker 2: is why everyone gets so excited.
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Speaker 3: This is the holy grail of quantum computing. A normal
11:24
Speaker 3: quantum bit aquibit is ridiculously fragile. The slightest vibration a
11:29
Speaker 3: little bit of heat, and the quantum information is lost.
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Speaker 3: It's called decoherence. But if you could build a quibit
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Speaker 3: out of these fractional stakes bulletproof, it would be topologically protected.
11:39
Speaker 3: The idea is you could literally braid these quasi particles
11:43
Speaker 3: around each other to perform calculations, and because the information
11:47
Speaker 3: is stored in the global topology of the braid local
11:50
Speaker 3: noise couldn't mess it up.
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Speaker 2: So a fault tolerant quantum computer.
11:54
Speaker 3: The dream of a fault tolerant quantum computer.
11:56
Speaker 2: Yes, okay, so let's just recap the stakes here. We
11:59
Speaker 2: want this fractional quantum hall state because it's dissipationless, no heat,
12:04
Speaker 2: and it's topologically stable, which is great for computing. But
12:07
Speaker 2: there has always been this one giant show stoffing catch
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Speaker 2: the magnet, the giant room size credit card erasing magnet.
12:16
Speaker 3: Exactly, you cannot put a fifteen tesla magnet inside your iPhone.
12:19
Speaker 3: It's just not going to happen. So for forty years
12:21
Speaker 3: this has been this beautiful laboratory curiosity. Look what amazing
12:26
Speaker 3: things nature can do. Moment, but not a Let's build
12:28
Speaker 3: a product with this moment.
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Speaker 2: Which brings us to the churn insulator. This is the
12:32
Speaker 2: proposed solution to the magnet problem, at least in theory.
12:35
Speaker 3: In theory, yes, a churn insulator is a type of
12:39
Speaker 3: material that, through its own internal quantum mechanics, essentially creates
12:44
Speaker 3: its own magnetic environment. The specific arrangement of the atoms
12:48
Speaker 3: and the way the electrons wave functions interact. It generates
12:51
Speaker 3: an effective magnetic field.
12:53
Speaker 2: So it's like virtual reality for electrons. They think they're
12:57
Speaker 2: in a massive magnetic field. Yeah, so they start doing
12:59
Speaker 2: the quant the Hall dance even though there's no external magnet.
13:02
Speaker 3: That is a fantastic analogy. Yes, a property of the
13:06
Speaker 3: material's electronic structure called Barry curvature acts just like a
13:10
Speaker 3: magnetic field. So you get the protected edge states, you
13:12
Speaker 3: get the one way super highway, you get the zero
13:15
Speaker 3: resistance all at zero external magnetic field.
13:19
Speaker 2: And that's the anomalous part of the name quantum anomalous
13:21
Speaker 2: Hall effect anomalists because the magnet is missing.
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Speaker 3: Correct. So bringing it all back to this week's paper,
13:27
Speaker 3: Sue and his team have been chasing the ultimate prize,
13:30
Speaker 3: not just a quantum anomalous Hall effect, but a fractional
13:33
Speaker 3: quantum anomalist Hall effect.
13:35
Speaker 2: Right. They want the material that has the fractional charges,
13:38
Speaker 2: the one third steps and works with no magnet.
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Speaker 3: That is the goal, a dissipationless fractional churn insulator.
13:45
Speaker 2: And they actually tried to publish this before, didn't they.
13:47
Speaker 2: I was looking at the timeline back in twenty twenty three.
13:49
Speaker 2: They had a paper that claimed they found it, but
13:52
Speaker 2: looking back now, it seems like that was a close
13:55
Speaker 2: but no cigar moment.
13:56
Speaker 3: Oh, it was a heartbreaking moment for the field. Honestly, Ujin,
14:00
Speaker 3: you're a scientist. You spend years designing and building this
14:03
Speaker 3: incredibly complex device. Cool it down. You measure it, and
14:07
Speaker 3: you see it. You see the plateau and the Hall
14:10
Speaker 3: resistance that screams one third fractional charges here.
14:14
Speaker 2: You pop the fambage, you.
14:15
Speaker 3: Pop the champagne. But then then you look at the
14:18
Speaker 3: other measurement. You measure the longitudinal resistance.
14:21
Speaker 2: Okay, remind us again. Hall resistance is the measurement across
14:24
Speaker 2: the current, the one that gives you the nice steps.
14:25
Speaker 3: Longitudinal resistance is it's the resistance along the direction of
14:29
Speaker 3: the current flow. In a perfect dissipationless state. This number
14:34
Speaker 3: should be zero, a flat line at the bottom of
14:37
Speaker 3: your graph, no question.
14:38
Speaker 2: And in their twenty twenty three experiment.
14:40
Speaker 3: It wasn't zero. It was something. It was small, but
14:43
Speaker 3: it was definitely measurably not zero.
14:46
Speaker 2: So the pipe was leaky.
14:47
Speaker 3: The pipe was leaky, exactly. They had the right general idea.
14:50
Speaker 3: The electrons were trying to do the collective dance, but
14:53
Speaker 3: the dance floor was too messy. They were tripping. They
14:56
Speaker 3: were bumping into things. Energy was leaking out as heat.
14:59
Speaker 3: It was not dipationless.
15:00
Speaker 2: I imagine for a physicist in this field, kind of
15:03
Speaker 2: dissipationless is like being kind of pregnant. It's a binary thing.
15:08
Speaker 2: It's either zero or it isn't.
15:10
Speaker 3: Absolutely in this game, if there's any resistance, it means
15:13
Speaker 3: the topological protection is broken. It means there are what
15:17
Speaker 3: we call dissipative channels that the electrons are finding. So
15:21
Speaker 3: for the last three years, big question in the community
15:23
Speaker 3: hasn't been is the theory wrong? The question has been
15:27
Speaker 3: is our sample just too dirty?
15:28
Speaker 2: Too dirty? I love that we're talking about the most
15:31
Speaker 2: esoteric quantum mechanics imaginable, and the problem comes down to
15:34
Speaker 2: basically dirt.
15:36
Speaker 3: Atomic scale dirt disorder in the crystal.
15:38
Speaker 2: Okay, so let's move on to that section three engineering
15:42
Speaker 2: the solution. How did they clean up the dirt? Because
15:45
Speaker 2: this is where the story shifts from abstract physics to
15:48
Speaker 2: really hardcore hands on material science. It really does They
15:52
Speaker 2: used of material called molybdenum detailur ride or multi two
15:55
Speaker 2: to two? Why this particular stuff? Why not good Old's silk?
16:00
Speaker 3: Well, silicon is great for what it does, but it's
16:02
Speaker 3: electronically kind of boring for this kind of work. MOTI
16:06
Speaker 3: two to two is part of a class of materials
16:08
Speaker 3: called transition metal decocogenis or TMDs, And the key thing
16:13
Speaker 3: about them is that they're layered materials like graphite. You
16:16
Speaker 3: can literally peel them apart into sheets that are just
16:19
Speaker 3: a few atoms thick.
16:21
Speaker 2: So they're effectively two dimensional.
16:22
Speaker 3: Exactly two D. And the real magic happens when you
16:25
Speaker 3: take two of these atomically thin sheets and stack them
16:28
Speaker 3: on top of each other. But you don't just stack
16:31
Speaker 3: them like two pieces of paper. You twist them.
16:33
Speaker 2: This is the famous tristronics.
16:35
Speaker 3: This is twistronics. It sounds like a nineteen eighties dance move,
16:38
Speaker 3: but it's one of the hottest fields in physics right now.
16:41
Speaker 3: When you rotate that top layer relative to the bottom
16:43
Speaker 3: layer by a very specific tiny angle, in this case
16:46
Speaker 3: somewhere around three degrees, you create something called a more pattern.
16:49
Speaker 2: I've seen this in the real world. If you look
16:51
Speaker 2: through two layers of fine mash, like two window screens,
16:55
Speaker 2: and you move your head, you see these weird, bigger,
16:59
Speaker 2: wavy patterns that aren't in the original mesh.
17:01
Speaker 3: Yes, that is an optical more pattern. In these stacked crystals,
17:06
Speaker 3: the twisting creates an electronic maree pattern. It's a giant
17:11
Speaker 3: periodic superlattice for the electrons, and this pattern fundamentally changes
17:16
Speaker 3: the energy landscape they live in. It creates what physicists
17:20
Speaker 3: call flat bands.
17:21
Speaker 2: Okay, flat bands, This feels like a key concept. We
17:25
Speaker 2: really need to nail down. What does a flat energy
17:27
Speaker 2: band do to an electron? Right?
17:30
Speaker 3: So, in a normal material, the energy band is curved.
17:33
Speaker 3: That means an electron can have a wide range of
17:35
Speaker 3: kinetic energies. It can zoom around at all.
17:37
Speaker 2: Different speeds, free to move.
17:38
Speaker 3: It's free to move, and it's kinetic energy dominates its life.
17:41
Speaker 3: It's running around so fast that it doesn't really have
17:43
Speaker 3: time to interact or care about the electron next to it.
17:46
Speaker 2: Too busy running to chat with the neighbors.
17:48
Speaker 3: Exactly. But in a flat band, the more superlattice essentially
17:52
Speaker 3: traps the electrons. It dramatically quenches or flattens their kinetic energy.
17:57
Speaker 3: They slow down to a crawl. They all have roughly
17:59
Speaker 3: the same very low energy, and because they aren't zooming
18:03
Speaker 3: around anymore, suddenly the most important force in their life
18:06
Speaker 3: isn't their own speed, it's the electrostatic repulsion from all
18:10
Speaker 3: their neighbors.
18:11
Speaker 2: The chat with the neighbors becomes the loudest thing in
18:13
Speaker 2: the room.
18:14
Speaker 3: The interaction energy becomes dominant, and that is the absolute
18:18
Speaker 3: prerequisite for the fractional quantum hall state. You need strong
18:22
Speaker 3: interactions to force the electrons into that collective correlated dance.
18:27
Speaker 3: The twist creates the flat band, and the flat band
18:30
Speaker 3: turns on the interactions.
18:31
Speaker 2: Okay, so they knew they need a twisted mo call
18:32
Speaker 2: two too. Back in twenty twenty three, they had that recipe.
18:35
Speaker 2: So what change between then and now? What was the
18:38
Speaker 2: big breakthrough?
18:39
Speaker 3: It was two things. First, they realized their starting ingredients,
18:42
Speaker 3: the crystals themselves, just weren't good enough. Even though they
18:45
Speaker 3: looked perfect under a normal microscope at the atomic level,
18:48
Speaker 3: they were full of defects the dirt. So they changed
18:51
Speaker 3: the recipe for how they grew the crystals. And this
18:54
Speaker 3: is where we have to give huge credit to the
18:56
Speaker 3: materials scientists on the team, specifically Ginhachu post doc Chohwehu.
19:02
Speaker 3: They switch to a different growth method called horizontal flux growth.
19:06
Speaker 2: How is that different from the usual way they make
19:08
Speaker 2: these things?
19:08
Speaker 3: Well, the more common way is something called chemical vapor transport.
19:12
Speaker 3: You basically heat up the raw powder, it turns into
19:14
Speaker 3: a gas, It drifts down a tube to a cooler spot,
19:17
Speaker 3: and it crystallizes on a surface. It's fast and it's
19:20
Speaker 3: pretty efficient, but it's a bit chaotic. Atoms can kind
19:24
Speaker 3: of slam into place. Sometimes they land in the wrong spot,
19:27
Speaker 3: creating a defect.
19:28
Speaker 2: It sounds like the fast food version of crystal growth.
19:31
Speaker 3: That's not a bad analogy. Horizontal flex growth is the
19:34
Speaker 3: slow cooked, artisanal, farm to table version. You dissolve the
19:38
Speaker 3: raw molybdenum and tellurium powder and a molten solvent, a
19:41
Speaker 3: liquid salt called a flux. It's a big liquid bath,
19:44
Speaker 3: and then you cool that entire bath down incredibly slowly.
19:47
Speaker 3: We are talking fractions of a degree over many hours
19:50
Speaker 3: or even days.
19:51
Speaker 2: It's like making perfectly clear ice for a fancy cocktail.
19:54
Speaker 2: If you freeze water really fast, it gets cloudy and
19:58
Speaker 2: full of imperfections. If you freeze is it super super slowly,
20:01
Speaker 2: it comes out crystal clear.
20:03
Speaker 3: That is the perfect analogy. By cooling it so slowly
20:07
Speaker 3: that atoms have time to find their absolute lowest energy position,
20:11
Speaker 3: they can wiggle around and slot themselves perfectly into the
20:14
Speaker 3: crystal lattice, no vacancies, no misaligned atoms, just perfection.
20:20
Speaker 2: And did it actually make a difference in the final product.
20:22
Speaker 3: A monumental difference. They measured a property called charge carrier mobility,
20:26
Speaker 3: which is basically a measure of how easily electrons can
20:29
Speaker 3: move through the material without scattering. It's a proxy for
20:32
Speaker 3: crystal quality. It increased by more than an order of magnitude,
20:36
Speaker 3: more than ten times better than the crystals they were
20:38
Speaker 3: using in twenty twenty three.
20:40
Speaker 2: Wow. All from just being more patient during the growth process.
20:43
Speaker 3: All from improving the fundamental ingredients. But that was only
20:46
Speaker 3: half the battle. You can have a perfect, flawless crystal,
20:49
Speaker 3: but you still have to perform the twist and the
20:52
Speaker 3: act of peeling, cutting and stacking these three atom thick
20:55
Speaker 3: layers is well, it's violent.
20:58
Speaker 2: I can't even imagine trying to twist some thing that
21:00
Speaker 2: thin without getting wrinkles and folds all over it.
21:02
Speaker 3: It's an absolute nightmare. And this was the second major
21:05
Speaker 3: problem in twenty twenty three twist angle disorder. Imagine you
21:09
Speaker 3: need that magic more pattern, which requires say exactly three
21:14
Speaker 3: point seven degrees of twist. But in the twenty twenty
21:17
Speaker 3: three devices, the twist angle wasn't uniform across the whole sample.
21:20
Speaker 3: One corner might have been at three point six degrees,
21:23
Speaker 3: the middle at three point seven, and the other corner at
21:25
Speaker 3: three point eight.
21:26
Speaker 2: So the flat band isn't actually flat everywhere it's warped.
21:29
Speaker 3: It's warped. The physics changes from one spot to the next.
21:33
Speaker 3: So an electron moving across the device hits these patches
21:36
Speaker 3: of the wrong angle and it scatters. It breaks the magic,
21:38
Speaker 3: it ruins the topological protection.
21:40
Speaker 2: So how did they iron out the wrinkles? Literally?
21:42
Speaker 3: A student on the team he on June Park gets
21:45
Speaker 3: the credit here. They refine the fabrication technique. They developed
21:47
Speaker 3: a new stamping method that uses specific polymers to handle
21:50
Speaker 3: the layers, reducing mechanical stress and ensuring the tension is
21:54
Speaker 3: perfectly uniform as the pop layer is laid down.
21:56
Speaker 2: So, okay, let's put it all together. They have the
21:59
Speaker 2: slow frozen eyes, ice perfect crystal, and they have the
22:02
Speaker 2: perfectly ironed out uniform twist. This is the twenty twenty
22:06
Speaker 2: six device. The moment of truth arrives.
22:09
Speaker 3: The moment of truth they put the new device in
22:12
Speaker 3: the cryostat, they cool it down to base temperature just
22:15
Speaker 3: millikelvin above absolute zero. They apply the gate voltage to
22:19
Speaker 3: tune the electron density to exactly two thirds filling.
22:23
Speaker 2: Why two thirds specifically.
22:25
Speaker 3: That just happens to be one of the known sweet
22:27
Speaker 3: spots where these fractional states are predicted to be most stable.
22:30
Speaker 3: It means, for every three units of magnetic flux in
22:33
Speaker 3: the Maire super lattice, you have two electrons. It's a
22:36
Speaker 3: particular stable configuration for the dance.
22:39
Speaker 2: Okay, two thirds filling. They flip the switch, they start
22:41
Speaker 2: measuring the resistance.
22:42
Speaker 3: What happens, The hall resistance jumps up and forms a
22:45
Speaker 3: perfect quantized placateau, exactly where theory says the two thirds
22:50
Speaker 3: fractional state should be. That's the good news, same.
22:52
Speaker 2: As twenty twenty three so far. But what about the
22:54
Speaker 2: other one, the longitudinal resistance, the heat loss.
22:57
Speaker 3: It drops to zero, a flat line, fixed flat line.
23:01
Speaker 3: It vanishes into the noise floor of their measurement equipment.
23:05
Speaker 3: In the twenty twenty three paper, there was a clear bump,
23:08
Speaker 3: a peak of resistance there. In the twenty twenty six paper,
23:12
Speaker 3: it is a beautiful flat line at.
23:15
Speaker 2: Zero they did it. A dissipationless fractional churn insulator.
23:18
Speaker 3: They did it, and the significance of this really cannot
23:21
Speaker 3: be overstated. They have proven definitively that you do not
23:25
Speaker 3: need an external magnetic field to get this exotic quantum state.
23:30
Speaker 3: They've proven that the key variable was always material quality.
23:34
Speaker 2: It validates the entire field of twistronics completely.
23:37
Speaker 3: It shows that by engineering these more a patterns, we
23:40
Speaker 3: can create and control some of the most bizarre and
23:43
Speaker 3: wonderful phases of matter imaginable.
23:45
Speaker 2: So if I'm a listener at home, I'm probably asking, Okay,
23:47
Speaker 2: this is super cool physics, but when does this get
23:49
Speaker 2: into my laptop and stop it from burning my legs?
23:51
Speaker 3: Well, we should be clear there are still some major hurdles.
23:53
Speaker 3: The biggest one is temperature.
23:55
Speaker 2: Right, this is still all happening at near absolute zero.
23:57
Speaker 3: It is we are not at room temperature yet, but
24:00
Speaker 3: the size of the energy gap they measured is promising.
24:04
Speaker 3: It suggests that with further improvements we could push that
24:07
Speaker 3: operating temperature up. But the more immediate application isn't about
24:11
Speaker 3: power lines or laptops, not yet.
24:13
Speaker 2: It's the quantum computer.
24:15
Speaker 3: It's the quantum computer. Remember the braiding the enions.
24:18
Speaker 2: The topologically protected quivots.
24:20
Speaker 3: Yes, now that we have a physical platform where these
24:24
Speaker 3: enians demonstrably exist without needing a giant magnet, we can
24:28
Speaker 3: start to actually design circuits. You could, in principle, etch
24:32
Speaker 3: tiny pathways on this Maditude two chip and use electric
24:35
Speaker 3: fields to shuttle these fractional quasi particles around, braid them
24:40
Speaker 3: around each other, and perform a computation.
24:42
Speaker 2: A computation that doesn't just collapse into dust when you
24:44
Speaker 2: look at.
24:44
Speaker 3: It's funny exactly. This transforms topological quantum computing from a
24:48
Speaker 3: beautiful theory on a blackboard into a tangible hardware platform.
24:52
Speaker 3: It's a chip, it exists, it's sitting in a lab
24:54
Speaker 3: in Seattle right now.
24:55
Speaker 2: That is just incredible butt. And there's always a butt
24:58
Speaker 2: in these big discovery stories. As I was reading through
25:00
Speaker 2: the notes here, there's a section labeled the scientific mystery.
25:04
Speaker 3: Ah. Yes, the thermal activation Gap.
25:06
Speaker 2: It sounds like the title of a Robert Ludlam thriller,
25:09
Speaker 2: The thermal activation Gap.
25:11
Speaker 3: It is a thriller, at least for the condensed matter theorists,
25:14
Speaker 3: because what they found when they dug deeple into the
25:16
Speaker 3: data makes absolutely no sense. Based on the old rules
25:20
Speaker 3: of the game.
25:21
Speaker 2: So set the scene for us. They have the device,
25:23
Speaker 2: it's working, zero resistance. The champagne has been popped, and
25:28
Speaker 2: then they decide to just mess with it.
25:30
Speaker 3: Scientists always mess with it, that's the job. They asked
25:33
Speaker 3: a very logical question. Okay, this state is perfect at
25:36
Speaker 3: zero magnetic field, but what happens if we add a
25:39
Speaker 3: small magnetic field?
25:40
Speaker 2: Now, based on everything we just talked about with the
25:42
Speaker 2: original quantum Hall effect, the magnet is the friend. The
25:46
Speaker 2: magnet is what creates the state in the first place,
25:49
Speaker 2: So adding more magnet should make the state even stronger, right,
25:53
Speaker 2: more robust.
25:54
Speaker 3: That is exactly the intuition everyone had in a standard
25:57
Speaker 3: fractional quantum Hall system in say alium arsenide, if you
26:01
Speaker 3: increase the magnetic field, you increase the gap.
26:03
Speaker 2: Okay, define gap for us again quickly. Yeah, the thermal
26:06
Speaker 2: activation gap.
26:07
Speaker 1: Right.
26:08
Speaker 3: Think of the gap as the width of a moat
26:10
Speaker 3: protecting a castle. Inside the castle, all the electrons are
26:14
Speaker 3: safe and sound in their perfect fractional state. Outside the
26:18
Speaker 3: moat is chaos. To destroy the state, an enemy like
26:22
Speaker 3: thermal energy has to kick an electron all the way
26:25
Speaker 3: across the moat.
26:26
Speaker 2: So a wider moat, a larger energy gap is better. Yeah,
26:29
Speaker 2: it means the castle is more secure, the state is
26:31
Speaker 2: more stable.
26:32
Speaker 3: Precisely, so, they turn on the magnetic field, expecting the
26:35
Speaker 3: moat to get wider. It got narrower.
26:37
Speaker 2: It shrank. The magnet made the state weak.
26:39
Speaker 3: It collapsed. As they slowly cranked up the magnetic field
26:43
Speaker 3: from zero, the thermal activation gap dropped rapidly. It became
26:47
Speaker 3: easier to destroy the state. The magnet, their old friend
26:50
Speaker 3: was actively attacking the stability of this new state.
26:53
Speaker 2: That is completely backwards from how it's supposed to work.
26:56
Speaker 3: It is profoundly counterintuitive. There's a line in the paper
26:59
Speaker 3: where you and the team right to our surprise, which
27:02
Speaker 3: is you know, scientists code for we were completely baffled.
27:05
Speaker 3: And this makes no sense. The gap decreased quickly and
27:07
Speaker 3: then eventually plateaued at a lower value.
27:10
Speaker 2: So what is the theory. Why if the magnet is
27:13
Speaker 2: supposed to help, why is it hurting. Here?
27:16
Speaker 3: The leading hypothesis, and it is just a hypothesis at
27:19
Speaker 3: this point, involves a kind of civil war inside the
27:23
Speaker 3: quantum state itself.
27:24
Speaker 2: A civil war, yes.
27:25
Speaker 3: A competition between different quantum properties of the electrons. In
27:30
Speaker 3: these TMD materials, electrons don't just have charge and spin
27:34
Speaker 3: up or down. They also have another property called valley valley.
27:37
Speaker 2: What's that.
27:38
Speaker 3: In the momentum energy landscape of the crystal, there are
27:40
Speaker 3: two distinct lowest energy valleys where electrons can live. They're
27:44
Speaker 3: called the K and K prime valleys. You can think
27:47
Speaker 3: of it as another quantum number, like another flavor of spin.
27:50
Speaker 2: So electrons have spin and they have flavor basically. Yes.
27:53
Speaker 3: Now, the magnetic field is very good at one thing.
27:56
Speaker 3: It loves to align spin. A magnetic field wants all
27:58
Speaker 3: the electrons spins to point in one direction. That's the Zeman effect.
28:01
Speaker 2: Okay, that makes sense. It's aligning all the little internal magnets, right.
28:05
Speaker 3: But the theorists think that the stability of the fractional
28:09
Speaker 3: state in this specific twisted material might depend on a
28:13
Speaker 3: very particular arrangement of the valleys. It might want the
28:16
Speaker 3: valleys to be polarized or mixed in a certain way
28:19
Speaker 3: that has nothing to do with spin.
28:20
Speaker 2: And the magnet comes in and messes up that valley
28:23
Speaker 2: arrangement exactly.
28:23
Speaker 3: The magnet storms in and says, attention, everyone, aligned by
28:26
Speaker 3: your spin. But the delicate fractional state says no, wait,
28:31
Speaker 3: we need to be aligned by our valley to maintain
28:33
Speaker 3: this collective dance. The two orders are competing. The magnet
28:37
Speaker 3: is forcing the system into a spin configuration that is
28:41
Speaker 3: not the optimal configuration for the valley based fractional state.
28:45
Speaker 2: So the mote shrinks because the very foundation of the
28:48
Speaker 2: castle is shaking from this internal conflict.
28:50
Speaker 3: That is a brilliant way to put it. The shrinking
28:52
Speaker 3: gap is the experimental evidence that the topology of this
28:55
Speaker 3: new state is much more complex and richer than the
28:58
Speaker 3: simple quantum hollow effect. It's born from this weird interplay
29:02
Speaker 3: of spin, valley and the more physics.
29:05
Speaker 2: So does this new mystery Does it ruin the discovery
29:09
Speaker 2: at all?
29:10
Speaker 3: Not at all. In many ways, it makes it even
29:12
Speaker 3: more exciting. It's a giant sign post that says new
29:15
Speaker 3: physics here. It means we don't fully understand what we've created,
29:19
Speaker 3: and that's the best place to be in science.
29:21
Speaker 2: It's not a bug, it's a feature.
29:23
Speaker 3: It's a new discovery that's come along for the ride.
29:26
Speaker 3: It gives us a new knob to turn and a
29:28
Speaker 3: new puzzle to solve.
29:29
Speaker 2: This brings us to the final section the future outlook,
29:33
Speaker 2: Shaodong Shoe seems incredibly optimistic. In the paper's conclusion, he
29:37
Speaker 2: has this great quote, the quantum hall community has made
29:41
Speaker 2: repeated breakthroughs by improving sample quality over the last forty years.
29:45
Speaker 3: That's the clean lens philosophy of science.
29:48
Speaker 2: Explain what you mean by that.
29:49
Speaker 3: Think of early astronomers looking at the sky through a dirty,
29:52
Speaker 3: low quality telescope. You see a faint, fuzzy blur. You
29:56
Speaker 3: might think that blur is a single star. But then
29:58
Speaker 3: you spend years grinding a better lens, making it cleaner
30:02
Speaker 3: and more perfect. Okay, you look through the new clean
30:05
Speaker 3: lens and you realize that blaur wasn't a star at all.
30:08
Speaker 3: It was an entire galaxy, or it was binary star system.
30:11
Speaker 3: The dirt in your instrument was hiding the true, more
30:14
Speaker 3: complex reality.
30:16
Speaker 2: The dirt hides the details.
30:18
Speaker 3: For forty years, the atomic scale, dirt and disorder in
30:21
Speaker 3: our materials has been hiding the true bizarre nature of
30:25
Speaker 3: interacting electrons. As we clean the lens with these incredible
30:29
Speaker 3: techniques like horizontal flux growth and low disorder fabrication, we
30:34
Speaker 3: aren't just making things more efficient, We are revealing new
30:37
Speaker 3: laws of physics that were hidden in the noise.
30:40
Speaker 2: Zoo follows that up by saying, we hope that the
30:42
Speaker 2: progress on this new platform will be even faster.
30:45
Speaker 3: And I think he's right to be optimistic, because now
30:47
Speaker 3: we have a recipe. It's not a mystery anymore. We
30:49
Speaker 3: know the key ingredients. High purity MOTI two two, the
30:52
Speaker 3: flux growth method, the low disorder twist. Any lab in
30:55
Speaker 3: the world with the right equipment can now start making
30:57
Speaker 3: these high quality devices and exploring.
31:00
Speaker 2: So the floodgates are about to open.
31:01
Speaker 3: People can try different twist angles, different layer fominations, different
31:05
Speaker 3: TMD materials. It really feels like we are standing on
31:08
Speaker 3: the beach of a new continent and we've just figured
31:10
Speaker 3: out how to build the boats.
31:11
Speaker 2: I want to circle all the way back to where
31:13
Speaker 2: we started this conversation. That hot phone in your pocket,
31:16
Speaker 2: that roaring data center.
31:17
Speaker 3: The radiator world we live in.
31:19
Speaker 2: It really feels like we are living in the steam
31:22
Speaker 2: age of computing. It's loud, it's hot, it's incredibly inefficient.
31:26
Speaker 3: We absolutely are. We are brute forcing electrons through solid
31:29
Speaker 3: rock and just dealing with the heat as a waste product.
31:32
Speaker 2: In this research, this dissipationless fractional churn insulator. This feels
31:38
Speaker 2: like the first real glimpse of the solid state silent electric.
31:43
Speaker 3: Future it is. It's a future where electrical current flows
31:46
Speaker 3: like a superfluid, where heat becomes an engineering choice, not
31:50
Speaker 3: an inevitable byproduct, where quantum information isn't stored on a material,
31:55
Speaker 3: but is braided into the very fabric of the material itself.
31:59
Speaker 2: It's just mind blowing stuff, and the fact that this
32:01
Speaker 2: is happening now in twenty twenty six makes me incredibly
32:04
Speaker 2: excited to see what the landscape looks like by twenty thirty.
32:07
Speaker 3: The pace of discovery here is just breathtaking.
32:10
Speaker 2: I think I want to leave our listener with one
32:11
Speaker 2: final thought, tom all over. We often look for the
32:13
Speaker 2: next big thing in a new app or a new
32:15
Speaker 2: gadget design, but sometimes the biggest revolutions are completely invisible.
32:20
Speaker 2: They're happening at the atomic scale inside a tiny flake
32:23
Speaker 2: of crystal that has been twisted just right.
32:25
Speaker 3: The twist is the key.
32:27
Speaker 2: Thank you so much for walking us through this. I
32:29
Speaker 2: feel like I finally actually understand what a churn insulator is.
32:32
Speaker 3: It was my absolute pleasure. This is the kind of
32:34
Speaker 3: stuff that makes being a physicist fun and.
32:36
Speaker 2: To everyone listening, thank you for being part of this exploration.
32:40
Speaker 2: Keep your devices cool, stay curious, and we will see
32:43
Speaker 2: you in the next deep dive.