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Scientists Detect a Hidden Form of Magnetism for the First Time · The Quark Side - Quantum Physics Podcast

• 0:01
  Speaker 1: Welcome to the Quarkside Quantum Physics Podcast, an exploration of
• 0:05
  Speaker 1: 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: You know, if you take a standard scientific probe and
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  Speaker 2: you hold it right up to an octopolar magnet, your
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  Speaker 2: instruments are going to tell you it's completely dead.
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  Speaker 3: Yeah, absolute zero magnetic field.
• 0:37
  Speaker 2: Right, exactly zero. Like it registers as entirely inert to
• 0:40
  Speaker 2: the outside world. But hiding inside that, well, that seemingly
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  Speaker 2: dead crystal is this completely bizarre quantum state. One that
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  Speaker 2: actually has eight competing magnetic poles existing all at once.
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  Speaker 3: Which is just mind-bending when you really think about it.
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  Speaker 2: It really is. And today, we are getting into a
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  Speaker 2: major breakthrough from a team of physicists at the University
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  Speaker 2: of Toronto. They finally figured out how to, you know,
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  Speaker 2: actually capture this invisible state. And they did it using
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  Speaker 2: twisting light to trigger these tiny, microscopic atomic spirals.
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  Speaker 3: Right, because the overarching challenge with these higher-order magnetic states,
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  Speaker 3: it isn't just their tiny physical scale. It's that their
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  Speaker 3: specific geometry actively hides them from the traditional ways we
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  Speaker 3: measure the universe.
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  Speaker 2: Okay, let's unpack this for a second. We all know
• 1:25
  Speaker 2: the classic fridge magnet, right?
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  Speaker 3: The good old dipole.
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  Speaker 2: Exactly, the dipole. Two poles, it's like a simple AA
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  Speaker 2: battery with a plus and a minus or a north
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  Speaker 2: and a south. But what does an eight-pole magnet even
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  Speaker 2: look like? I mean, is it like a microscopic 3D
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  Speaker 2: compass pointing in eight different directions at once inside a crystal?
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  Speaker 3: Yeah, that's actually a pretty great way to visualize it.
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  Speaker 3: What's fascinating here is that this isn't just a single
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  Speaker 3: atom acting weird. It's an emergent collective behavior across the
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  Speaker 3: entire crystal structure.
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  Speaker 2: Oh, so the structure itself is doing this.
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  Speaker 3: Exactly. You have to picture the crystal not as a
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  Speaker 3: solid brick, but as this intricate 3D grid of atoms.
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  Speaker 3: And the electrons in there have spin. In your standard
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  Speaker 3: fridge magnet, all those spins line up in parallel. They
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  Speaker 3: just point the exact same way.
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  Speaker 2: And I guess that creates the strong magnetic field we
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  Speaker 2: can easily measure.
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  Speaker 1: Right.
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  Speaker 3: But in an octopolar state, the spins arrange themselves in
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  Speaker 3: this highly complex alternating pattern. It's almost like a microscopic
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  Speaker 3: 3D checkerboard of magnetic moments.
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  Speaker 2: So they're all pointing in completely different diverging directions.
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  Speaker 3: Yes, and they perfectly balance each other out within the
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  Speaker 3: basic unit of the crystal. That perfect geometric balance is
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  Speaker 3: exactly why it registers as having zero macroscopic magnetic field.
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  Speaker 2: Wait, so it essentially has eight distinct poles that perfectly
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  Speaker 2: cancel each other out over any real distance. Exactly.
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  Speaker 3: And mathematically, physicists knew this state should exist in certain
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  Speaker 3: rare earth compounds. But proving it experimentally, that was considered
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  Speaker 3: almost impossible.
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  Speaker 2: Because, well, you can't find a footprint if the thing
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  Speaker 2: doesn't leave any tracks.
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  Speaker 3: Exactly right. You can't just sprinkle iron filings on it
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  Speaker 3: and see a neat little pattern.
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  Speaker 2: Right. Normal tools are totally useless here. Which is why
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  Speaker 2: the Toronto team had to get creative. They decided to
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  Speaker 2: stop looking for magnetic tracks and start looking for physical,
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  Speaker 2: mechanical ones. Specifically, they looked at phonons.
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  Speaker 3: Which is such an ingenious pivot.
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  Speaker 2: It really is. But I want to make sure we
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  Speaker 2: define phonons clearly here for anyone new to this. Wait,
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  Speaker 2: so a phonon isn't a physical particle like an electron, right?
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  Speaker 2: It's just a packet of vibration? Is it kind of
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  Speaker 2: like the physical ripples you see when you throw a
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  Speaker 2: stone into a pond, but frozen as a concept inside
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  Speaker 2: a crystal?
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  Speaker 3: Yes, that is a perfect analogy. If we connect this
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  Speaker 3: to the bigger picture, think of the crystal's internal structure
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  Speaker 3: as a microscopic network of masses and springs.
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  Speaker 2: Okay, so the atoms are the masses and the chemical
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  Speaker 2: bonds are the springs.
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  Speaker 3: You got it. And when energy hits that network, the
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  Speaker 3: atoms vibrate. That vibration pulls on neighboring atoms, creating a
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  Speaker 3: mechanical ripple that travels through the whole crystal. That traveling
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  Speaker 3: wave is the phonon. And the researchers used light, almost
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  Speaker 3: like a mallet striking a bell, to create those exact ripples.
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  Speaker 2: But why would physical vibrations reveal a magnetic state? That
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  Speaker 2: sounds like, I don't know, trying to find an electrical
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  Speaker 2: short by checking the room temperature.
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  Speaker 3: I mean, it sounds disconnected, sure, but they are relying
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  Speaker 3: on something called spin lattice coupling. The magnetic layout actually
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  Speaker 3: pulls and pushes on the atoms themselves. Oh, wow.
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  Speaker 2: So even though the magnetic field is canceled out from
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  Speaker 2: the outside... Inside the crystal, it's actually changing the tension
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  Speaker 2: of those microscopic springs.
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  Speaker 3: Exactly. It alters the spring constants. So when the crystal vibrates,
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  Speaker 3: the phonons are forced to travel through a physical structure
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  Speaker 3: that's been fundamentally warped by this invisible magnetic geometry.
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  Speaker 2: Here's where it gets really interesting. The researchers found that
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  Speaker 2: these vibrations had a very specific, bizarre characteristic.
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  Speaker 3: A handedness, right?
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  Speaker 2: They called them pseudochiral phonons.
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  Speaker 3: Yes, chirality is a massive concept here. It's like your
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  Speaker 3: left and right hands. They are mirror images, but you
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  Speaker 3: can't perfectly lay your left hand over your right hand.
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  Speaker 2: So the eight-pole magnetic state essentially forces the atomic vibrations
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  Speaker 2: to twist in a specific direction, like a microscopic spiral
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  Speaker 2: staircase that only spirals clockwise?
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  Speaker 3: Precisely. In a normal crystal, a vibration might just move
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  Speaker 3: straight back and forth. But here, the hidden magnetic order
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  Speaker 3: torques it. It forces the mechanical wave to spiral as
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  Speaker 3: it moves, and it actively stops it from spiraling the
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  Speaker 3: opposite way.
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  Speaker 2: Wait, let me challenge that for a second. If the
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  Speaker 2: crystal is completely magnetically dead to the outside world, how
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  Speaker 2: do we actually detect that spiral? I mean, they used light,
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  Speaker 2: but light is an electromagnetic wave. Shouldn't it just pass
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  Speaker 2: right through a magnetically dead crystal?
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  Speaker 3: That is the exact paradox they had to solve. And
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  Speaker 3: it raises an important question about how light, vibration, and
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  Speaker 3: magnetism interact. The incoming light isn't coupling to a macroscopic
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  Speaker 3: magnetic field, because there isn't one. It's interacting with the
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  Speaker 3: physical structure through a process called Raman scattering.
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  Speaker 2: Striking the bell to see how it rings, like we
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  Speaker 2: were saying earlier. Right.
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  Speaker 3: But to detect a twisting vibration, they needed a tool
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  Speaker 3: capable of interacting with twisting. So they used circularly polarized light.
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  Speaker 2: Where the light wave itself is basically spiraling forward?
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  Speaker 3: Exactly. It carries angular momentum. The rotating light acts like
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  Speaker 3: a key. fitting perfectly into the pseudochiral lock.
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  Speaker 2: Oh, I see. So if you hit the crystal with
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  Speaker 2: right rotating light and the crystal's hidden magnetic structure naturally
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  Speaker 2: wants to twist to the right, boom, you get a
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  Speaker 2: massive reaction.
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  Speaker 3: Exactly. They perfectly couple. The photon transfers its energy into
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  Speaker 3: the lattice. But if you hit it with left rotating light.
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  Speaker 2: It actively resists it.
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  Speaker 1: Yes.
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  Speaker 3: The incoming light tries to force the atoms to twist
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  Speaker 3: the wrong way. and the invisible magnetic architecture just shuts
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  Speaker 3: it down. By comparing how the crystal reacts to right
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  Speaker 3: versus left twisting light, they found the definitive fingerprint of
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  Speaker 3: the 8-pole magnet.
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  Speaker 2: That is just such an elegant workaround. They couldn't read
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  Speaker 2: the magnetic data, so they read the structural echo of
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  Speaker 2: the magnetic data instead.
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  Speaker 1: It's brilliant.
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  Speaker 2: Okay, so what does this all mean? Like, why should
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  Speaker 2: we care about this outside of a high-level physics lab?
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  Speaker 3: Well, it comes down to the future of our everyday technology.
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  Speaker 3: Moving from just detecting this quantum state to actually manipulating
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  Speaker 3: it is the holy grail. Our whole digital world right
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  Speaker 3: now is built on ferromagnets, normal two-pole magnets. Right.
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  Speaker 2: Up is a one, down is a zero.
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  Speaker 3: Exactly. But as we try to pack more and more
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  Speaker 3: data onto smaller hard drives, we are hitting a hard
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  Speaker 3: physical wall. If you put normal dipoles too close together,
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  Speaker 3: their magnetic fields project outward and interfere with each other.
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  Speaker 2: They just start flipping adjacent bits and scrambling the data.
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  Speaker 3: Exactly. You get total data corruption. But an octopolar magnet
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  Speaker 3: has no external field to cause that interference. Oh, wow.
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  Speaker 2: So if a normal hard drive writes data in simple
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  Speaker 2: ones and zeros based on a two-pole magnet, does mastering
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  Speaker 2: an eight-pole magnet mean we can pack exponentially more data
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  Speaker 2: into the exact same space? Is this the secret to
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  Speaker 2: super-dense futuristic computing?
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  Speaker 3: It absolutely is. You can pack these memory bits... Mere
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  Speaker 3: nanometers apart. And they wouldn't even know the other bits existed. Plus,
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  Speaker 3: an 8-pole geometry inherently means you could have multiple stable
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  Speaker 3: configurations in the exact same footprint. It wouldn't just be
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  Speaker 3: binary anymore.
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  Speaker 2: Wait, really? So you could hold way more nuanced information
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  Speaker 2: than just a single 1 or a 0 in each spot.
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  Speaker 3: Exactly. And it wouldn't just be denser. It would be
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  Speaker 3: wildly resilient. You could drag a powerful magnet right over
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  Speaker 3: this kind of hard drive, and the data wouldn't care
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  Speaker 3: at all. The external field just doesn't couple to the
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  Speaker 3: hidden internal state.
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  Speaker 2: That resilience sounds exactly like what we need for quantum computing,
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  Speaker 2: doesn't it? Because I know traditional quantum qubits are famously fragile.
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  Speaker 2: Like a tiny temperature change or a stray magnetic field
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  Speaker 2: and the whole quantum state just instantly collapses.
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  Speaker 3: Decoherence. Yeah, it's the single biggest hurdle in quantum tech
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  Speaker 3: right now. We currently have to hide qubits inside massive,
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  Speaker 3: super-cooled metal dilution refrigerators just to keep them somewhat stable.
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  Speaker 2: So could an octopolar material act as a naturally stable
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  Speaker 2: qubit since it inherently ignores outside magnetic noise?
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  Speaker 3: It is a prime candidate for it. It functions like
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  Speaker 3: a mechanical vault where the internal lock is so complex
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  Speaker 3: that random environmental noise just can't accidentally click the tumblers open.
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  Speaker 3: You need the exact specific key, like that perfectly tuned
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  Speaker 3: twisting laser pulse, to even begin to alter the data.
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  Speaker 2: That is... incredible. So the moment you can reliably see
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  Speaker 2: the phenomenon, you can actually start engineering it.
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  Speaker 3: Always. History shows us that constantly. Seeing the electron gave
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  Speaker 3: us electronics. Understanding the dipole gave us modern hard drives.
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  Speaker 3: Unlocking these pseudo-chiral phonons paves the way for vastly more
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  Speaker 3: powerful decoherence-resisting computers. We are totally reframing how we view
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  Speaker 3: solid materials. They aren't just static rocks sitting on a desk.
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  Speaker 2: Right. They're these incredibly dynamic quantum arenas just constantly negotiating
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  Speaker 2: fundamental forces.
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  Speaker 1: Right out of sight.
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  Speaker 3: And the apparent macroscopic solidity of a crystal is just
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  Speaker 3: an illusion of our immense scale.
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  Speaker 2: Well, that is a perfect summary. We started with that
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  Speaker 2: simple two-pole magnet on your fridge and traveled all the
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  Speaker 2: way down to hidden eight-pole quantum states, discovered just by
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  Speaker 2: using rotating light to trigger twisting atomic vibrations.
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  Speaker 3: A masterpiece of indirect observation.
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  Speaker 2: It really is. And I want to leave you with
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  Speaker 2: one final lingering thought to ponder on your own today.
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  Speaker 2: If scientists are just now finding practical ways to see
• 11:03
  Speaker 2: octopolar magnetism, you know, this fundamental force that's just been
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  Speaker 2: sitting completely invisible to us, And they're doing it using
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  Speaker 2: something as simple as light and vibration. Well, what other
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  Speaker 2: bizarre higher order structures of matter are sitting right in
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  Speaker 2: front of us? Completely invisible, simply because we haven't invented
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  Speaker 2: the exact right flashlight to look at them yet.
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  Speaker 3: We are truly just scratching the surface of what is
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  Speaker 3: structurally possible out there.
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  Speaker 2: We absolutely are. Keep looking closely at the invisible mechanics
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  Speaker 2: of the world around you. Keep asking those big questions.
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  Speaker 2: And most importantly, stay curious. We'll catch you next time.