Are quantum computers already super-powerful?
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Today we're looking at a number that, a little bit like Schrodinger's cat, is either a massive number or not a massive number, depending on whether the story holds together. It was sent in by listener David Lawrence, who asked us to look into a figure he'd seen in the press coverage of a new quantum computer chip being developed by Google.

Here's the claim. Chip takes minutes to complete tasks that would otherwise take 10 septillion years. That's 10 with 24 zeros after it, which, as the article in The Guardian newspaper explains, is a length of time that far exceeds the age of our known universe. So it's definitely a big number. But does it mean a new breed of quantum computer is here?

one that will make a normal computer look like an abacus and be able to do scary things that no ordinary computer can do, like break Bitcoin by cracking all encryption. First things first, what the hell is a quantum computer? A quantum computer is a machine which...

harnesses the laws of quantum mechanics to solve certain computing problems. That's Dr Peter Leake, a researcher at Oxford University and Chief Scientific Officer at quantum computing company Oxford Quantum Circuits. To understand a quantum computer, you first need to understand the ordinary bog-standard classical computer that's in your laptop and smartphone.

If you look right deep inside the computer, you're not going to see letters and words. Those words will all be represented by strings of ones and zeros. At a basic physical level, computation is all about moving electricity around the wires on a circuit board.

There'll be some way those ones and zeros are represented, like there'll be a high voltage or a low voltage on the wire. There'll be a kind of string of pulses going along the wire. These long strings of pulses of high or low voltage contain a stream of information. In the language of computing, the unit of information, that thing which can be either one or zero, that's known as a bit.

8 bits make a byte. And thanks to logic and maths and code, with these ones and zeros, all these megabytes of data processing and storage, you can create virtual reality worlds, artificial intelligence and an email. The words in your emails, absolutely everything is boiled down to being represented by ones and zeros. So that's a classical computer. What's different with a quantum computer?

Well, for starters, it's built out of something a bit different. Not just standard brass wires and a circuit board, but superconductors kept at incredibly low temperatures. It turns out that if you try to build circuits from superconductors...

and you cool them to extremely low temperatures, you can make those circuits fully obey the laws of quantum mechanics in a way that you can use for quantum computing. Now, the laws of quantum mechanics describes the frankly weird behaviour of our world at the very smallest scales. Now, we don't have time to go all Ant-Man and get into the weeds of this here, so we're just going to explain what obeying these laws means in practice for a computer.

That goes back to the bits, the stream of zeros and ones. And for a quantum computer... That thing which can be zero or one can also be zero and one at the same time. I'm going to repeat that. The bits in a quantum computer can be both zero and one at the same time.

This is just what happens when quantum mechanics kicks in at very small scales. And I'm afraid you're just going to have to go along with it. The maths works. It describes the results of the scientific experiments that are done.

you accept the counterintuitive nature of it. Moving on, and this bit of quantum mechanics means that basically, instead of being in a fixed position of 1 or 0, the quantum bits in the circuit, or qubits as they're known, are in what's known as a superposition of both 1 and 0 simultaneously.

Because of this weird fact, the complexity of the calculations the quantum computer can do multiplies up very fast. Instead of the simple strings of zeros and ones... The number of possible states that are represented there are now all the possible strings of zeros and ones. ...all the possible combinations, which quickly produces numbers that are... More than the number of atoms in the universe for not too many bits.

OK, enough of the basics of quantum computing. Either you get it or you don't, or maybe both at once. Time for that very big seeming number. Remember, Google claim their quantum chip could process something in five minutes that it would take a normal computer 10 septillion years. What did Dr Leak make of that? My first reaction when I see that number is it's hype.

It's not wrong, but it's hype. The key thing to understand is that they're not talking about the quantum chip being able to do just any calculation that much faster. Yeah, so that's 100% not true. So quantum computers are not just faster computers. They are a certain type of computer, a very specific type of computer that will be able to do certain types of calculation

faster than classical machines. But it's certainly not a machine which will do all of computing faster than any other. And in fact, in terms of raw speed, quantum computers, as are built currently, are not really fast.

when compared to classical machines. Indeed, there are many computational processes that a normal computer could do in five minutes, but which would take one of these quantum computers 10 septillion years or whatever. Yes, absolutely. Absolutely. And I think it's probably fair to say there are far more of those than the other way around right now. Right. So what about the specific tasks that the Google quantum chip did in five minutes?

Should we still be impressed? It's a result of thinking very carefully about what computational task could be run on a quantum computer that is very difficult for a classical computer to run.

And the thing which has been found is this thing called random circuit sampling. This seems to basically involve taking snapshots of the processing that's happening in a quantum computer, which is obviously pretty easy for a quantum computer, and incredibly hard for a normal computer stuck in its binary world. This is not a useful thing to be able to do. It's not virtual worlds or artificial intelligence or even email. And to be fair to Google and their chip...

Peter says they were pretty clear about all of this. If you read carefully what they say, they don't hide that it isn't useful. If you only read the headline, you can draw conclusions that the machine is more useful than it is when you read the full information. Now, Peter obviously does think quantum computers are a good thing. One of his jobs is at a quantum computing company after all. But it all needs a bit more time. I think we're very likely to see in about five years' time, roughly, a

things starting to emerge which are much more clearly of value than these sort of esoteric things which people are showing right now. In the even longer run, it's possible quantum computers will be able to do some very hard computation, where that superposition weirdness is super valuable and super scary. For example, it could break all online encryption. But for Peter, the best fit for quantum computing is the quantum universe itself.

using it to figure out how stuff works at the very, very small scales where quantum mechanics operates. So quantum computers might be able to find new materials, new medicines, that kind of thing. It might seem that simulating quantum mechanics is a kind of fringe thing that we might not find uses for, but simulating quantum mechanics is important for such a huge range of things. So, I mean, it's important for understanding physics,

chemistry, materials, ultimately pharmaceuticals. So if we want to understand how a drug interacts with the body. That's where quantum computers might go. The way there are likely to be some massive and reasonably meaningless numbers. That's it for this week. Please get in touch if you've seen a number we should look at. The email is more or less at bbc.co.uk. Until next time, goodbye.

When you have bars in the sky, onboard showers and award-winning in-flight entertainment, it's no surprise that Emirates was recently named the best airline in the world. We fly you to over 140 destinations and with partners across the globe, we connect you to another 1,700 cities across six continents. So when we say we're also the largest international airline, what we really mean is...

If you're going there, so are we. Book now on emirates.com. Fly Emirates. Fly better. Yoga is more than just exercise. It's the spiritual practice that millions swear by.

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