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A beginner’s guide to quantum computing | Shohini Ghose


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)

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