Leo Kouwenhoven is a professor in Applied Physics specialized in the field of Quantum NanoScience. His team at the QU Tech Lab designs experiments to place electrons in superpositions.
Here is the full text of Leo’s talk titled “Can we make quantum technology work?” at TEDxAmsterdam.
Leo Kouwenhoven – TEDx Talk Transcript
Good morning, everybody.
Does anybody recognize the picture behind me? What is it? That computer — it was in fact, a mechanical computer, the computer that was used by Alan Turing, which helped to end the Second World War.
What is interesting is that here the wheels are turned, and by registering clicks and no clicks, they could break encrypted messages. So it’s a mechanical motion that actually can do some calculations for us.
Now we use of course electronic computers, where electrical signals encode for our bits zeros and ones. But clicks or no clicks, or zeros and ones, actually is the same principle for encoding information, no difference between the Turing machine and our computers.
What is amazing is that — and what happened in the last 50-60 years is that this machine now fits around your wrist, and it sells as a SmartWatch – the same computing power. Anybody else who has a SmartWatch here? I see a few. Aha! So you fell for the same commercial as I did, I guess.
But it’s smaller, and you see that the revolution in making things smaller is very visible, but what is maybe even more amazing is that the underlying principles of the Turing machine of clicks and no clicks, and in my SmartWatch, it’s still the same; that has not changed – clicks or no clicks, zeros or ones.
Some time ago, a very interesting new idea started to become popular. And there’s not really a single inventor, and in fact, it is not really an invention, it’s rather a change of perspective and the idea is that nature also calculates.
For instance, when light hits a green leaf, it induces all kinds of chemistry, which at the end of the chemistry reaction, it produces oxygen among other things. And the process in between the input light and the output oxygen can be viewed as a calculation.
Why this is an interesting change of perspective is because nature actually calculates a lot faster and a lot smarter than our computers do. The key ingredient that nature uses is, in fact, quantum mechanics.
And the beautiful thing of quantum mechanics is that you don’t have to be a zero or a one, you can be zero and one at the same time, and this option of being zero and one at the same time is used in nature. Zeroes and ones at the same time that they sound acceptable, but clicks and no clicks at the same time that is absurd.
Nevertheless, people like me started to use these principles of quantum mechanics to build a new very powerful computer, it’s called a quantum computer.
How does the quantum computer work?
Why is it actually good? That’s going to be my story today.
Let me first tell you a little bit about myself. I grew up in a small town in the Netherlands on a farm. I was actually doing okay in high school, and I was allowed to go to university. But the only people in my town that I knew who had a university degree was our town veterinarian and our priest.
Now, becoming a priest was not an option for me, so I was going to become a vet. However and unfortunately, my university had no entrance exam, but instead a lottery, which I lost, so I ended up at my second choice which was physics. But my roots remain.
As a farmer son, I keep this pragmatic approach. And nowadays as a professor, if I hear some of my colleagues make very profound theoretical predictions, I think, “Wow, that sounds profound.” Can we actually do something useful with it? And that is also my attitude towards quantum mechanics.
And quantum mechanics is certainly among the most profound scientific ideas that we have around. People like Bohr, and Einstein, discovered the deeper principles of quantum mechanics about 100 years ago. And those principles of quantum mechanics are absurd for us, humans, but not for small particles like electrons.
So what a small particle like an electron can do is for instance not be confined to one single point in space, it can actually occupy different points in space at the same time. How that is possible is actually very impossible to explain in words in our language.
The best thing we can do is just accept that what is absurd for us, is OK for small particles like electrons. So think about this for a moment, because it’s actually very essential for my story that a single particle, the single object can actually be at different locations at the same time. We call this superposition.
When you accept superposition, then you can actually also understand things like chemistry. For instance, a very simple example – the oxygen molecule, and we draw it like two oxygen atoms that are held together by these horizontal lines in the oxygen molecule.
What do these horizontal lines actually stand for?
Well, they share an electron, but this electron does not sit still in the middle between these two atoms. No, it actually divides itself up, goes into a superposition, and occupies the space around each of these two oxygen atoms.
Since these two parts of the same single-electron doesn’t want to be too separated, it actually keeps the oxygen atoms together, so it’s actually a superposition that binds atoms in molecules. Since actually our body consists of molecules, so without superposition, our body would fall apart; and without superposition, all our molecules would fall apart in loose atoms.
So superposition is a good thing. You should like it on Facebook.
Since Einstein, and Bohr, and also other genius scientists developed the principles of quantum mechanics, we’ve been using mostly formulas — formulas to describe nature, as it is given to us.
But now 100 years later, it’s actually time for something new. We now view nature as an information processor, and instead of formulas, we use this symbol to describe that there is an information flow in nature.
And we no longer study nature as it is given to us. We actually have started to design and construct actual subprogram — the machines that we make ourselves; and study how our own designed machines can actually solve quantum problems.
So my job has become to make qubits. Instead of a farmer, instead of a vet, I have become a qubit maker, or a superposition maker. And I want to illustrate that with electrons in boxes.
What you see here in the upper row are two boxes and one electron. In our world, that electron has to choose it can sit on the left or in the right box. In an information description of the same thing, what we say is that in the upper case, when the electron is in the left box, I call it a bit zero; or if it’s in the right box, I call it a bit one. This is actually how we encode information in our normal computers – that’s a bit zero and a bit one.
The special thing that we do in our lab in Delft, is that we can do also superposition. So we can take a single electron and put it in both boxes at the same time, kind of similar the oxygen at a molecule. But now we’ve boxes that we have made ourselves, and if we can also control and program.
When the electron is in both boxes at the same time, in an information description, we say the system is in a qubit state, and the qubit is in a superposition of a bit zero and a bit one at the same time. So it encodes for that information at the same time.
If we have these qubits, we made actually a little animation to illustrate how it can be used to speed up calculations. You see here a labyrinth, and if we put a classical electron into this labyrinth, then the way electrons actually solve classically this problem to find the exit of the labyrinth is what we would do. We try path by path. Every time, we find it’s not the solution, we try again.