Leo Kouwenhoven on "Spooky" Physics at TEDxDelft (Full Transcript)

Leo Kouwenhoven, professor in Applied Physics discusses “Spooky” Physics at TEDxDelft – Transcript

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TRANSCRIPT:

They just told me back there that apparently there is a golden rule in book publishing that says that with every formula you show, you lose half of your audience. And I have two in my first slide.

But I only want to show you these formulas to illustrate that with just a few symbols, like F = m x a, we can describe a wealth of phenomena, from the Earth around the Sun, from a ball game, from your bike ride, everything.

Or if you are a communication person, you may like Maxwell’s equation. Everything we do with our radio or mobile phone, communications or actually the fact that we see each other, is all described by this very simple Maxwell equation that you see here. It is so simple. It describes basically these two equations. It describes basically everything in our daily life.

But there is more. Besides our classical world, there is also a quantum mechanical world. This is the world of atoms, molecules, the very small particles. And again, we have a very simple looking equation. It has a Greek symbol in it, that makes it a little bit obscure, but otherwise it is fairly short.

And please be impressed, that this equation, the Schrödinger’s equation, describes all of Chemistry. So in some sense, because our bodies are big chemical factories, with all the atoms held together by quantum mechanical glue, our existence is thanks to quantum mechanics.

But maybe with this third equation I am losing another half of the audience. Many people think: “Oh, these small particles are not my things.” Or “Formulas, I never have understood them. I am more of the human scale.

I feel things or hear things or even touch things.” In that case, you are the right person for me to talk to because I will not show any more formulas in my presentation. I will actually show you some quantum objects that you can actually see, you can actually hear them, and you can touch them. So let’s start.

It all starts, actually, up to a few minutes ago, before I came on the stage, quantum mechanics was describing very well, very accurately the world of atoms and molecules. Then, at large scale, it had already started at our unit, the biological cell, it kind of stops. The biologist takes the cell as the fundamental unit to build up biology. This is an enormous simplification because it completely ignores quantum mechanics. But it is as best as we can do at this moment. Larger objects like our hair, which is basically the smallest thing we can see with our eyes, or us, you know, that is all classical.

But the small things can be described very accurately. The people who put forward this theory, the quantum theory, actually maybe made the greatest intellectual revolution of mankind. You see a picture here on the first row, very prominent Albert Einstein. You can clearly recognize him in the middle. On his right, left for us, there is Hendrik Lorentz, our Dutch hero. And next to Lorentz, you see Madame Curie. And many of these men in this picture have received a Nobel Price for their great work. There is one person who got the Nobel price twice. And that is actually the only woman in the picture, Madame Curie. So apparently that is true what they say that women have to perform twice as good in order to be part of the gang. She did it. This is a hundred years ago.

What’s new? Well, present day geniuses look like this. This is a group of brilliant people that form our group at the TU Delft. But again, they are at the verge of a new quantum era. We are no longer studying atoms and molecules as given by nature, a concept that we actually design and make, by using very advanced fabrication techniques, new objects, much bigger, but still showed us this absurd quantum mechanical behavior.

So what is actually absurd about quantum mechanics? Why are we so excited about our quantum stuff? Let me give you two examples of absurd quantum mechanics. The first example is quantum superposition. Let’s take a particle, like an electron or something, and bring it into a ring structure. Have the particle then take either the upper arm to get to the exit or take the lower arm to get to the exit.

Now, what actually happens in quantum mechanics is that the electron takes both arms at the same time simultaneously, really sitting in the upper arm as well as in the lower arm at the very same time. And we know this because we follow the particle and we see that at the exit of the ring it actually collides with itself. It bounces into itself. And we observe this as interference. Such a superposition of being at two different locations at the same time has been very thoroughly checked by all kinds of experiments. Quantum superposition.

The next example is an example of entanglement. And we start very simple. We take, say, a red particle and a white particle. Very classical colors. Then the next step is that we bring them together and we make them interact a little bit. So we bring them very close together so they feel each other. By virtue of this interaction they become entangled; they take over each other’s properties. In terms of color they become white-reddish. That’s OK.

The curious thing that happens if we take them, and disentangle them again and bring them apart. And while taking them apart they remain entangled. They are still — the one that is on the left for you, still has some properties of the other particle, which can be at a very large distance, as far as the size of the Universe, in principle. So let’s disentangle them over a very long distance. Particles keep having each other’s properties.

So what can we do? Can we actually measure it? Well, the problem is that if we measure it, we have a classical color measurement apparatus. And the color measurement apparatus is a classical thing that can only give classical answers. So it says that it is red or white. So I say, well, particle on the left, what is actually your color? And I measure it. It has reasons to say red. Maybe you notice that the particle on the right at the same moment became white. Let’s check it again. I measure the left particle, and the one on the right immediately becomes white. That’s because color is a conserved quantity in the Universe. So if something completely turns red, something else which it used to be entangled with is completely turning white. And this action, over a large distance – and remember it — can be the size of the Universe. These particles can be apart, it takes place instantaneously.

Let me put it there. A measurement of the color on the left particle, immediately changes also the color that is far away. So if I do something here, and at the same time I change something there without any signals traveling over, to actually say, well, you just go there. There is nothing in between. Much faster than the speed of light. So this is a prediction from quantum theory. And one guy, Einstein, said: “That must be wrong. Any theory that predicts spooky action on a distance, do something here, change something there, that is a prediction that tells that the theory is wrong.” He doesn’t say it is possible, tells the theory is wrong.

Luckily we also have other heroes in physics. This is a theoretical physicist called Richard Feynman. And he said, “Let’s not be bothered with all these philosophical consequences of our theory. Let’s calculate and see what happens.” And here, at the Delft University of Technology, we educate engineers, actually guys like me, and our approach is that if you feel challenged, we say, okay let’s do it.

So what do we do? We take these two particles, we bring them far apart and we make it a bit more complicated; we bring in a third particle, the green one. The green one we bring to the left one and we make these two interact. We kind of give them some interaction and view the graph carefully. You see that at the same moment, when these two interact and share some color, also the particle on the right, which was still entangled with the first one, also becomes green a little bit.

The next is that I ask for color, “Hey, the left particles, I do a color measurement,” and they for instance become white reddish. At the same time, the one on the right becomes green. So look what I’ve done effectively. Let’s start again. I bring in a green particle, they entangle. They also entangled with the one on the right. I click once more and the one on the right is now green. I have teleported the green particle from the left universe to the right universe over a long distance instantaneously. So this teleportation is, what we call, absurd, strange or very odd.

But we can do it, and we actually do it. And actually we do this in the lab. We have actually done it so many times that we actually made a student proof setup. I can tell you, if a setup is a student proof, then it is a very robust setup. All right.

So what do we make? We want to make some stuff that we can actually use and do something with it. First of all, a very simple example of a light bulb. It is a plain wire; we send a current through the wire, or it gets excited by light, it also luminesces a little bit of its light. But in this case the wire is very small; it is only nanometers in diameter, maybe a micrometer long. At the red arrow that you see we excited system with some laser light. We actually look what comes out of the wire. If you do that, you actually see a little bit of light coming out of the thing. Right? That bright spot.

Now, what is special about this bright spot is that if you analyze it with a good detector, it actually comes out as a stream of individual light particles, one by one. It is no longer a stream of light; it is really granular; one comes out, the next one comes out, et cetera. And these are our photons that we use in this color experiment to teleport.

Let me give you another example. Different type of — if you are more of a hearing person, let me take a string. With all our strings, guitar or a violin, whatever, you put a tension on the string, the tone of the music goes up in frequency. The tone goes up. So we have taken a very thin wire, a nanotube, only one nanometer in diameter, we suspend it over a trench, we clamp it very tightly at two contacts and we excite the nanotube with an electric pulse. It starts to vibrate and we hear the tone.

Now, what is special about this particular vibration is that it is very small. It is also very sensitive. So if we add one electron, one quantization of electrical charge, to this nanotube. It is a little bit of extra tension into the nanotube, that changes the tone a little bit. Let me hear the sounds of the electron (whistle sound). The composition could be a bit more interesting, but the change in tone, if you go from one level to the next level, that change is induced by one particular individual electron. You hear. Let us hear it again. What you hear are individual quantum electrons (whistle sound) And it becomes audible.

Let me give you the most recent example that comes straight from the lab of my colleague Leonardo DiCarlo. Actually we need to do something for this. Because we have — DiCarlo lab actually made a box. You see the box already on the picture, on the upper right, with a few correctional connectors to it. And if I get my gloves on, it’ll actually let me touch the box. And the box is big. I can hold it in my hands. What we do in our group is to make small electronic elements that are so small that they can process information in a completely different way. Instead of having bits of zeros and ones, we want to make superpositions of bits, that superposition of being zero and one at the very same time.

But you want to make them on an electronic circuit. And what Leo DiCarlo has done is to make three cubits. I am going to zoom in a little bit in a few seconds. But you’ve already seen the box with three cubits in it. And these three cubits can be put in a superposition or be entangled together in any arbitrary way that we wish. Let me see if the camera can actually show you the cubits. There must be more zoomed. This is my finger. That is the size of the system. I hope you can see that there are three black spots on this quartz plate. And these three black spots are about a centimeter away from each other. And these are our cubits – the cubits which are in quantum superposition, and we can entangle different cubits together. We are now on a chip of centimeter size. The distance between the different cubits is about a centimeter. And we can perform all these quantum absurdness on this chip at a visible length scale. All right.

So you’ve seen it. Now of course it only works if the details are fabricated very precisely, and the details are on nanometer scale. So it is not just that every centimeter object starts to behave quantum mechanically. But you really have to engineer it very precisely down to the nanometer scale. That is a picture that you see right here.

Let me zoom out a little bit. What are we trying to do here? We actually want to make quantum mechanical systems and use the richness of quantum systems like the extra possibilities of being superpositions and having very fast teleportation over long distances. Also in technology we make applications that are much more efficient than we have today. And particularly because we are in the quantum information business, we want to extend the level of quantum from the atom to a transistor, that is already the case. That is working very well.

But we want to bring even up to a higher level of complexity at a complete electronic circuit that behaves quantum mechanical. And it will win so much in efficiency you would not believe it. And that would also make our gadgets a lot faster.

Now, only a few years ago, people often in our field were saying, that is not going to happen, that is inherently impossible as quantum mechanics to bring them up to a larger scale of size and complexity. With the progress of the last few years, I can really say here, actually I am saying it for the first time in public this clear that it will come. Yes. We will be able to make quantum circuits and a quantum computer will only take maybe a decade later or so.

All right. Let me conclude here with a take home message. I started this with some equations, including one for quantum mechanics, but there is one message, that up to a couple of minutes ago quantum was only restricted to the small objects, but from now on, it has arrived to the human scale. And we can see it, we can hear it and we can touch it.

Thank you very much. And have a great day.

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Leo Kouwenhoven on “Spooky” Physics at TEDxDelft (Full Transcript)

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