Boaz Almog "levitates" a superconductor

772,929 views ・ 2012-07-02

TED


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Translator: Morton Bast Reviewer: Thu-Huong Ha
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The phenomenon you saw here for a brief moment
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is called quantum levitation and quantum locking.
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And the object that was levitating here
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is called a superconductor.
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Superconductivity is a quantum state of matter,
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and it occurs only below a certain critical temperature.
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Now, it's quite an old phenomenon;
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it was discovered 100 years ago.
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However, only recently,
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due to several technological advancements,
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we are now able to demonstrate to you
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quantum levitation and quantum locking.
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So, a superconductor is defined by two properties.
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The first is zero electrical resistance,
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and the second is the expulsion of a magnetic field from the interior of the superconductor.
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That sounds complicated, right?
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But what is electrical resistance?
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So, electricity is the flow of electrons inside a material.
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And these electrons, while flowing,
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they collide with the atoms, and in these collisions
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they lose a certain amount of energy.
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And they dissipate this energy in the form of heat, and you know that effect.
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However, inside a superconductor there are no collisions,
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so there is no energy dissipation.
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It's quite remarkable. Think about it.
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In classical physics, there is always some friction, some energy loss.
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But not here, because it is a quantum effect.
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But that's not all, because superconductors don't like magnetic fields.
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So a superconductor will try to expel magnetic field from the inside,
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and it has the means to do that by circulating currents.
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Now, the combination of both effects --
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the expulsion of magnetic fields and zero electrical resistance --
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is exactly a superconductor.
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But the picture isn't always perfect, as we all know,
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and sometimes strands of magnetic field remain inside the superconductor.
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Now, under proper conditions, which we have here,
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these strands of magnetic field can be trapped inside the superconductor.
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And these strands of magnetic field inside the superconductor,
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they come in discrete quantities.
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Why? Because it is a quantum phenomenon. It's quantum physics.
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And it turns out that they behave like quantum particles.
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In this movie here, you can see how they flow one by one discretely.
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This is strands of magnetic field. These are not particles,
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but they behave like particles.
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So, this is why we call this effect quantum levitation and quantum locking.
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But what happens to the superconductor when we put it inside a magnetic field?
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Well, first there are strands of magnetic field left inside,
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but now the superconductor doesn't like them moving around,
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because their movements dissipate energy,
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which breaks the superconductivity state.
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So what it actually does, it locks these strands,
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which are called fluxons, and it locks these fluxons in place.
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And by doing that, what it actually does is locking itself in place.
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Why? Because any movement of the superconductor will change their place,
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will change their configuration.
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So we get quantum locking. And let me show you how this works.
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I have here a superconductor, which I wrapped up so it'd stay cold long enough.
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And when I place it on top of a regular magnet,
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it just stays locked in midair.
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(Applause)
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Now, this is not just levitation. It's not just repulsion.
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I can rearrange the fluxons, and it will be locked in this new configuration.
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Like this, or move it slightly to the right or to the left.
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So, this is quantum locking -- actually locking -- three-dimensional locking of the superconductor.
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Of course, I can turn it upside down,
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and it will remain locked.
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Now, now that we understand that this so-called levitation is actually locking,
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Yeah, we understand that.
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You won't be surprised to hear that if I take this circular magnet,
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in which the magnetic field is the same all around,
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the superconductor will be able to freely rotate around the axis of the magnet.
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Why? Because as long as it rotates, the locking is maintained.
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You see? I can adjust and I can rotate the superconductor.
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We have frictionless motion. It is still levitating, but can move freely all around.
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So, we have quantum locking and we can levitate it on top of this magnet.
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But how many fluxons, how many magnetic strands are there in a single disk like this?
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Well, we can calculate it, and it turns out, quite a lot.
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One hundred billion strands of magnetic field inside this three-inch disk.
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But that's not the amazing part yet, because there is something I haven't told you yet.
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And, yeah, the amazing part is that this superconductor that you see here
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is only half a micron thick. It's extremely thin.
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And this extremely thin layer is able to levitate more than 70,000 times its own weight.
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It's a remarkable effect. It's very strong.
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Now, I can extend this circular magnet,
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and make whatever track I want.
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For example, I can make a large circular rail here.
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And when I place the superconducting disk on top of this rail,
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it moves freely.
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(Applause)
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And again, that's not all. I can adjust its position like this, and rotate,
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and it freely moves in this new position.
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And I can even try a new thing; let's try it for the first time.
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I can take this disk and put it here,
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and while it stays here -- don't move --
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I will try to rotate the track,
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and hopefully, if I did it correctly,
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it stays suspended.
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(Applause)
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You see, it's quantum locking, not levitation.
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Now, while I'll let it circulate for a little more,
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let me tell you a little bit about superconductors.
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Now -- (Laughter) --
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So we now know that we are able to transfer enormous amount of currents inside superconductors,
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so we can use them to produce strong magnetic fields,
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such as needed in MRI machines, particle accelerators and so on.
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But we can also store energy using superconductors,
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because we have no dissipation.
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And we could also produce power cables, to transfer enormous amounts of current between power stations.
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Imagine you could back up a single power station with a single superconducting cable.
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But what is the future of quantum levitation and quantum locking?
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Well, let me answer this simple question by giving you an example.
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Imagine you would have a disk similar to the one I have here in my hand,
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three-inch diameter, with a single difference.
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The superconducting layer, instead of being half a micron thin,
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being two millimeters thin, quite thin.
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This two-millimeter-thin superconducting layer could hold 1,000 kilograms, a small car, in my hand.
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Amazing. Thank you.
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(Applause)
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