TED日本語 - ショヒーニ・ゴーシュ: 10分で分かる量子コンピュータ

Let's play a game. Imagine that you are in Las Vegas, in a casino, and you decide to play a game on one of the casino's computers, just like you might play solitaire or chess. The computer can make moves in the game, just like a human player. This is a coin game. It starts with a coin showing heads, and the computer will play first. It can choose to flip the coin or not, but you don't get to see the outcome. Next, it's your turn. You can also choose to flip the coin or not, and your move will not be revealed to your opponent, the computer. Finally, the computer plays again, and can flip the coin or not, and after these three rounds, the coin is revealed, and if it is heads, the computer wins, if it's tails, you win.

So it's a pretty simple game, and if everybody plays honestly, and the coin is fair, then you have a 50 percent chance of winning this game. And to confirm that, I asked my students to play this game on our computers, and after many, many tries, their winning rate ended up being 50 percent, or close to 50 percent, as expected. Sounds like a boring game, right?

But what if you could play this game on a quantum computer? Now, Las Vegas casinos do not have quantum computers, as far as I know, but IBM has built a working quantum computer. Here it is.

But what is a quantum computer? Well, quantum physics describes the behavior of atoms and fundamental particles, like electrons and photons. So a quantum computer operates by controlling the behavior of these particles, but in a way that is completely different from our regular computers. So a quantum computer is not just a more powerful version of our current computers, just like a light bulb is not a more powerful candle. You can not build a light bulb by building better and better candles. A light bulb is a different technology, based on deeper scientific understanding. Similarly, a quantum computer is a new kind of device, based on the science of quantum physics, and just like a light bulb transformed society, quantum computers have the potential to impact so many aspects of our lives, including our security needs, our health care and even the internet.

So companies all around the world are working to build these devices, and to see what the excitement is all about, let's play our game on a quantum computer. So I can log into IBM's quantum computer from right here, which means I can play the game remotely, and so can you. To make this happen, you may remember getting an email ahead of time, from TED, asking you whether you would choose to flip the coin or not, if you played the game. Well, actually, we asked you to choose between a circle or a square. You didn't know it, but your choice of circle meant "flip the coin," and your choice of square was "don't flip." We received 372 responses. Thank you. That means we can play 372 games against the quantum computer using your choices. And it's a pretty fast game to play, so I can show you the results right here.

Unfortunately, you didn't do very well.

(Laughter)

The quantum computer won almost every game. It lost a few only because of operational errors in the computer.

(Laughter)

So how did it achieve this amazing winning streak? It seems like magic or cheating, but actually, it's just quantum physics in action. Here's how it works. A regular computer simulates heads or tails of a coin as a bit, a zero or a one, or a current flipping on and off inside your computer chip. A quantum computer is completely different. A quantum bit has a more fluid, nonbinary identity. It can exist in a superposition, or a combination of zero and one, with some probability of being zero and some probability of being one. In other words, its identity is on a spectrum. For example, it could have a 70 percent chance of being zero and a 30 percent chance of being one or 80-20 or 60-40. The possibilities are endless. The key idea here is that we have to give up on precise values of zero and one and allow for some uncertainty. So during the game, the quantum computer creates this fluid combination of heads and tails,zero and one, so that no matter what the player does, flip or no flip, the superposition remains intact. It's kind of like stirring a mixture of two fluids. Whether or not you stir, the fluids remain in a mixture, but in its final move, the quantum computer can unmix the zero and one, perfectly recovering heads so that you lose every time.

(Laughter)

If you think this is all a bit weird, you are absolutely right. Regular coins do not exist in combinations of heads and tails. We do not experience this fluid quantum reality in our everyday lives. So if you are confused by quantum, don't worry, you're getting it.

(Laughter)

But even though we don't experience quantum strangeness, we can see its very real effects in action. You've seen the data for yourself. The quantum computer won because it harnessed superposition and uncertainty, and these quantum properties are powerful, not just to win coin games, but also to build future quantum technologies. So let me give you three examples of potential applications that could change our lives.

First of all, quantum uncertainty could be used to create private keys for encrypting messages sent from one location to another so that hackers could not secretly copy the key perfectly, because of quantum uncertainty. They would have to break the laws of quantum physics to hack the key. So this kind of unbreakable encryption is already being tested by banks and other institutions worldwide. Today, we use more than 17 billion connected devices globally. Just imagine the impact quantum encryption could have in the future.

Secondly, quantum technologies could also transform health care and medicine. For example, the design and analysis of molecules for drug development is a challenging problem today, and that's because exactly describing and calculating all of the quantum properties of all the atoms in the molecule is a computationally difficult task, even for our supercomputers. But a quantum computer could do better, because it operates using the same quantum properties as the molecule it's trying to simulate. So future large-scale quantum simulations for drug development could perhaps lead to treatments for diseases like Alzheimer's, which affects thousands of lives.

And thirdly, my favorite quantum application is teleportation of information from one location to another without physically transmitting the information. Sounds like sci-fi, but it is possible, because these fluid identities of the quantum particles can get entangled across space and time in such a way that when you change something about one particle, it can impact the other, and that creates a channel for teleportation. It's already been demonstrated in research labs and could be part of a future quantum internet. We don't have such a network as yet, but my team is working on these possibilities, by simulating a quantum network on a quantum computer. So we have designed and implemented some interesting new protocols such as teleportation among different users in the network and efficient data transmission and even secure voting.

So it's a lot of fun for me, being a quantum physicist. I highly recommend it.

(Laughter)

We get to be explorers in a quantum wonderland. Who knows what applications we will discover next. We must tread carefully and responsibly as we build our quantum future. And for me, personally, I don't see quantum physics as a tool just to build quantum computers. I see quantum computers as a way for us to probe the mysteries of nature and reveal more about this hidden world outside of our experiences. How amazing that we humans, with our relatively limited access to the universe, can still see far beyond our horizons just using our imagination and our ingenuity. And the universe rewards us by showing us how incredibly interesting and surprising it is.

The future is fundamentally uncertain, and to me, that is certainly exciting.

Thank you.

(Applause)