The Ultimate Parallel Processor: Quantum Bits

IRA FLATOW: This is Science Friday. I’m Ira Flatow.

Few things are more frustrating when you’re in a hurry to load a web page, than waiting and waiting for that little spinning beach ball to go away. You know what I’m talking about. Well, imagine trying to solve a problem that won’t take just a few minutes. No. How about a problem that would take the lifetime of the universe to solve. Like, oh, 14 billion years. I think I’d run out of patience by then.

But a different type of computer, a quantum computer, could solve that quandary way faster by harnessing the weird physics of the quantum world. And last week, researchers reported in the journal, Science, that they had built a quantum computer using only five atoms. And they say they could scale it up to a much larger, more powerful device.

Here to tell us about it is Krysta Svore. She’s a senior researcher and research manager at Microsoft Research in Redmond, Washington. And just a note, she wasn’t involved in this particular research paper. But she knows all about this kind of stuff.

Welcome to Science Friday, Dr. Svore.

KRYSTA SVORE: Thank you, Ira.

IRA FLATOW: Let’s talk about this paper. They built a quantum computer with five atoms. How does that work?

KRYSTA SVORE: Well, so what this research team did is they actually looked at using what we call an ion trap quantum computer. So they take an atom and then they remove, essentially, electrons to make it charged. And then they hold these atoms, suspend them in a trap. And this experiment, they built up in the lab.

And as you mentioned, with five atoms, they can run a very small quantum algorithm. Namely, an algorithm we call Shor’s algorithm that actually allows us to factor numbers. That is, to find the two prime numbers that you multiply together to get a number. And in their case, they looked at factoring the number 15, which, of course, they find to be five times three.

IRA FLATOW: Well, they didn’t need a quantum computer for that, though.

KRYSTA SVORE: Yeah. Yes, of course, we can solve that today on pretty much every device we have.

IRA FLATOW: Our phone number, 844-724-8255, 844-SCI-TALK. You can also tweet us @SciFri.

Now of course, that was a very simple factor of 15. But was it there just to demonstrate that it could be done?

KRYSTA SVORE: Well, that’s exactly right. This is really a demonstration of being able to perform a sequence– what we call a quantum circuit– of logic gates on these atoms that store information in a quantum mechanical way. So this is a start towards building up towards a larger algorithm.

And this algorithm factoring can actually do things once scaled up. It can do things like break the RSA cryptosystem. RSA, of course, is a mainstay of e-commerce today. It’s the predominant public key encryption system that we use on the internet. Every time you put your credit card on the internet it actually encodes it into this problem called factoring.

So being able to factor large numbers, much larger than 15, would in fact enable us to learn the credit cards being placed, for example, on the internet.

IRA FLATOW: And a quantum computer could potentially do that.

KRYSTA SVORE: That’s exactly right. Shor, Peter Shor, who is now a professor at MIT, actually found a quantum algorithm. So he found the mathematical theory and proved that if we have a quantum computer, indeed a quantum computer could solve this problem, and break RSA encryption.

IRA FLATOW: So we should assume the holy grail of computing is to come up with a working quantum computer.

KRYSTA SVORE: Yeah, I definitely see it as a holy grail of computing. Perhaps more exciting even than being able to solve something like factoring is the potential of a quantum computer for other problems outside of cryptography. Being able to do things that we simply can’t compute today, that may be able to solve some of the world’s largest problems.

Thinking about being able to more readily produce artificial fertilizer with less resources, less cost. Being able to extract waste carbon from the environment. These types of problems are very, very hard to solve and to study on digital computers, even supercomputers.

But a quantum computer actually promises to be able to solve some of these problems, or help solve some of these problems, like identifying a catalyst that would allow us to more efficiently capture carbon and help solve global warming. You know, that’s something we hope to solve on a scalable quantum computer.

IRA FLATOW: Now let’s try to talk about why. I know this is a difficult subject to get your head around. Why a quantum computer works differently than the normal digital computer. The ones and zeroes that we use now.

KRYSTA SVORE: Right. So our digital computers, when we dig down underneath the hood, a digital computer works on binary states. So we think of things in terms of zeros and ones. It’s like a light switch. When you think about a normal light switch, the light is on or off. You switch it on, you switch it off. That’s what’s happening in transistors in our digital computers.

But a quantum computer actually allows you to be in a continuous state. It allows you to be what we call in a superposition of states. So you can simultaneously, that’s at the same time, be in the zero state and the one state. That’s something we can’t do on digital computers. So the superposition is one of the things behind these quantum computers that really helps with the parallelism and the speed ups that we can achieve.

And of course, there’s other things we take advantage of as well. Quantum mechanical principles like interference, entanglement. The ability to entangle two quantum bits of information, send one across the universe– and when I actually perturb the state of my quantum bit that I held on to, it immediately does something to the quantum bit that was sent to the other side of the universe.

So we really take advantage of entanglement, this idea of interference, and this idea of superposition that gives us some parallelism.

IRA FLATOW: This is just so hard to fathom. How much more powerful a quantum computer is. Can you put a number? Is their a number of how much more powerful one is equal to the other?

KRYSTA SVORE: Yes. So in the case of a digital computer where we have just zeros and ones, and you can only be in the state zero or one– in the quantum computer, I can be in both states simultaneously. And this allows us to scale what we call exponentially better in terms of the storage capacity of the device. So if we can only store as a zero or a one, if we need to store both of those bits in a classical computer, we actually need to store the zero and the one in separate bits.

But quantum mechanically, we store both in the same bit of information, this qubit. So we get a problem that requires, say, N bits. We can store two to the N states in N qubits, instead of requiring a full N states for that amount.

IRA FLATOW: Getting into the weeds a little bit. But we like to do that. How much do you need to know to make a quantum computer? I guess what I’m asking is, can anybody with a Ph.D. Or an advanced computing or physics degree make a quantum computer at this point?

KRYSTA SVORE: Well, making a quantum computer at this time really requires some specialized experimental setups. And definitely, there are labs around the world working on this in various countries, including the United States. And this work that we’re speaking about today was done in Innsbruck, Austria, jointly with folks at MIT.

So really, you need some special experimental setups. In particular, you may need to be able to apply high magnetic fields. You may need a dilution refrigerator that operates at the coldest temperatures on Earth of minus 459 degrees Fahrenheit, for example. Not all of us have those refrigerators in our homes.

IRA FLATOW: No. I’m getting one next week. This week, Bill Gates held an ask me anything session on Reddit, where, in response to a question, he said, quote, “Microsoft and others are working on quantum computing. It isn’t unclear when it will work or become mainstream. There is a chance that within 6 to 10 years, cloud computing will offer super computation by using quantum.”

You know Bill Gates? You work there, over at Microsoft?

KRYSTA SVORE: Yes.

IRA FLATOW: I hope he’s listening. Quantum in the cloud. So the cloud would be made of quantum computers. Could you explain that?

KRYSTA SVORE: Well, I think perhaps one way to think about this is that a quantum computer is not going to be a device that’s sitting on your desk or in your pocket. It’s really more like a supercomputer. Right? You can actually connect with a supercomputer over a network, and then solve computations on that supercomputer. But the supercomputer is not sitting in your office.

Similarly, a quantum computer will be a resource that you could connect to in the cloud. So potentially, it would be sitting in a cloud environment. It’s not going to be physically in your office.

IRA FLATOW: We have some interesting questions on our phones. 844-724-8255. Let’s see if we can get to some of those questions. Let’s go to Jacob in Bay City, Michigan. Hi, Jacob.

JACOB: Hi, Ira. How you doing today?

IRA FLATOW: Hey there. Go ahead.

JACOB: Yeah. I work in IT and I do programming on the side. I’m just wondering, how is this going to translate into modern day architecture? Are we going to need new programming languages for quantum computers?

IRA FLATOW: All right, good question.

KRYSTA SVORE: That’s a wonderful question, and actually, something we’re working on here at Microsoft. So you’ll perhaps be happy to hear that we actually have a software architecture we recently released on GitHub. That actually allows you to program quantum circuits, quantum algorithms, and then actually simulate them on your classical, your digital hardware today, in advance of having a fully scalable quantum computer.

But indeed, your question raises the issues in programming and a very exotic hybrid technology. What’s really interesting about a quantum computer is it’s actually controlled by a digital computer. A potentially very large digital computer will actually control the quantum computer.

So when we think about a software architecture and a programming stack for a quantum computer, we really need to think about the fact that we will have mixed instructions. Both classical or digital instructions, as well as quantum instructions. And we’ll really have to build up a different set of compilation techniques than we have for our digital computers. And that’s something we’re addressing with a software architecture we call Liquid.

IRA FLATOW: Besides breaking codes and things, is there something in nature, a question about nature, the universe, that you know could be answered if you had a quantum computer? But we don’t have one yet.

KRYSTA SVORE: Right. So I think this is a great area for quantum computers to really have impact. Actually, going back to Feynman– even as early as the late 1950s, Feynman said, using something like a quantum computer, we’ll be able to better simulate physical systems and understand our world. In particular, understanding the ground state of a molecule, understanding dynamics of molecules, understanding these properties of molecules. It’s very, very hard to understand these on digital computers.

So I mentioned previously about carbon capture, about nitrogen fixation, which is a way to help produce catalysts and understand artificial fertilizer production. When we think about wanting to find a material that actually super conducts at room temperature, which would enable lossless power transmission, these questions are much better answered on a quantum computer than on a digital computer. Because in fact, on a digital computer, solving these problems could take longer than the lifetime of our universe, but only a mere hours or days of computation on a quantum computer.

IRA FLATOW: Now that certainly puts in perspective how strong a quantum computer is. It’s quite interesting. And it’s interesting to hear that Richard Feynman was still talking about– or how far back people were talking about quantum computers. Back in the 1950s.

I want to thank you for taking time to be with us today.

KRYSTA SVORE: Thank you so much for having me.

IRA FLATOW: Krysta Svore is a senior researcher and research manager at Microsoft Research in Redmond, Washington. Thanks again.

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