TEDxUCLA 2016: Push. Pull. Stretch.
How quantum computers are different
Let me begin to tell you a story. I was a fifth grader. One day my sister came to me and she said, “You’re just reading story books. It’s time to read some science.” Then she took me to a bookstore and bought me this book about atoms. And that was the beginning of my fascination with the world of quantum physics.
This journey continued. Twenty-five years later, now I’m a part of a team of scientists at Google and we are working to build a new type of computer based on principles of quantum physics.
What is quantum physics? In the 19th century, we had a good understanding of how nature works for a large object. For example, we could explain how the Earth moves around the sun or how steam can move a locomotive. But in the early 20th century, scientists started going deeper. They wanted to know that if we look at the tiniest building blocks of nature, like atoms or molecules, does nature still behave the same way as we humans sense it?
So they designed a number of clever experiments and they played with light interacting with matter and they found that what they observed in those experiments cannot be explained with the physics of the 19th century. So they invented new physical laws for nature, and these new laws are called principles of quantum mechanics, which are different from how we experience our world in our daily lives.
Let me tell you what one way that quantum physics tells us nature works, behaves differently from how we sense it. For us, any object that any moment of time had a certain position. Like I’m standing on this stage, I’m here. None of you see me at a different location in this room. I guess. But quantum physics tells us that for tiny objects like an atom, or like a particle, or like an electron, you cannot specifically say where they are located. If I want to exaggerate, like if I were in a particle like an electron, you couldn’t tell where I was standing. There was a chance that every one of you will find me at a different location in this room.
This property is called a superposition. That means being in all possibilities at the same time. We use this property of superposition to make faster computers. The computers that we have now, like our laptops or like my cell phone that I am using, a core of them is nothing but a bunch of electric switches that each electric switch can store one bit of data at a time. It can be either zero or one. Just one number. It’s pretty boring, because these computers are from the last century.
Now we can make a quantum switch. A quantum switch, or what we call the quantum bit, doesn’t need to be either zero or one, but it can be in a superposition of zero and one. It can absorb saw a combination of two numbers. So when we have a number of these quantum bits, they do not store or show just one binary number, but they can store a combination of all possible binary numbers. And that’s one main reason that quantum computers can compute certain things way way much faster than classical computers that we have.
Let’s make a simple comparison. Suppose we have a quantum computer with 400 quantum bits. Four hundred is a small number. Imagine: like, my cell phone has more than a billion bits. Classical bits. We are talking about 400 for quantum.
Now if we want to transfer the information or write down the information that is stored in 400 quantum bits, on a number of classical computers, like a number of laptops, how many laptops you can imagine we need to make this transfer of data from quantum to classical? Make a, use your imagination to make it wildest guess. Like a thousand, a million laptops, and a billion trillion.
The answer is that the number of laptops we need is more than the number of atoms in the whole visible universe. And that was only about storing the same amount of information.
So from this simple comparison you can see that it may take forever for a classical computer to do the same computation that a quantum computer with a few hundred quantum bits can do. Therefore, quantum computers will make some impossible calculations possible. I will talk more about this in a few minutes.
Now you may want to see what a higher quantum computer look like. This, in this picture you see a piece of quantum computer built by our hardware team in Santa Barbara. This electric circuit shows nine, this electric circuit of nine quantum bits, and each of those white crosses you see is the head of one of those quantum bits.
And actually I have it here, in this. In this box, there is a spot of size one centimeter wide by one centimeter. And this is basically the circuit that you see in this picture. You can come and find me and we’ll have a look at it. But with your bare eyes, you can see each of those quantum bits that you see in this picture.
Now you may say, “Wait a second: you are just telling us that quantum physics is important when we are talking about small objects and small sizes, but this is pretty large.” Well, I haven’t told you the whole story.
Quantum physics is, it becomes important and relevant, not only at small sizes but at low temperatures. So in principle we can take any object of any size and cool it down, and eventually it’ll start behaving like in quantum objects.
Imagine somehow this room becoming colder and colder. Suddenly, our bodies start going into superposition all over this room. So to make this electric circuit quantum, we put them in this special fridge. That this fridge cooled down the circuit to near-absolute zero temperature.
Inside this cylinder is the — one of the coldest places you can find in the whole universe. Okay, cool. So this is the… This seems to be an amazing technology you’re developing and it sounds this quantum computer would have some extraordinarily powerful computation.
But the main question is that how this computer can improve our daily lives, right? Because for us humans, when we make a new tool, we want to do something useful with that.
Now let me tell you how a quantum computer can have a serious impact on our daily life. This picture shows a basic cycle of food production in our ecosystem. In this chain between the nitrogen in the air and to the food that discovers consuming, there is an unsolved puzzle that the quantum computer can solve. What’s that? Nitrogen in the air is absorbed by some bacteria in the soil that, with some chemical process, turns nitrogen into ammonia. The details of this process, how nitrogen turns into ammonia, is unknown. And why it is important to find a solution for to find the answer for that because then we can learn from bacteria how to cheaply and efficiently produce ammonia that is widely used as fertilizer for agriculture.
Now where do quantum computers come into play to solve this puzzle? It all goes into solving the properties, finding the properties of this molecule, that plays a central role in conversion of nitrogen to ammonia. The challenge is that the classical computers that we have now are not capable to solve the equation that describes this molecule. Why? Because a molecule is a quantum system, and we know that a classical system are not abled or not capable to do a detailed modelling of even a quantum, even a small quantum system.
But that’s not a problem for a quantum computer. It’s natural for a quantum computer to solve the details of another quantum system like a molecule. And this was one example of how a quantum computer can seriously change the way we design molecules and new materials.
Therefore, from the material science perspective, quantum computers can have serious impact in helping us solving so often make major problems that we have in the world, like fighting global warming, making more efficient car batteries, or better drugs for our health industry.
With that I want to say stay tuned for big news from the world of quantum computers. Thank you.