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  • 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 cannot 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)

Let's play a game.

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B2 US TED quantum quantum computer computer coin flip

【TED】Shohini Ghose: A beginner's guide to quantum computing (A beginner's guide to quantum computing | Shohini Ghose)

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    林宜悉 posted on 2019/02/01
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