What’s So Great About Quantum Computing? Question and answer with NIST theorist Alexey Gorshkov

Alexey Gorshkov poses at a whiteboard, holding a marker.

Alexey Gorshkov is a NIST theorist who works at the intersection of physical and computer research.

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NIST

As the rise of quantum computers becomes the subject of more and more news articles – especially those that prophesy the ability of these devices to break the encryption that protects secure messages, such as our bank transfers – it is enlightening to speak with one of the quantum experts. who are actually developing the ideas behind these as yet unrealized machines. While ordinary computers work with bits of data that can be either 0 or 1, quantum computers work with bits – called quits – that can be 0 and 1 at the same time, enabling them to perform certain functions exponentially faster, such as testing the different “keys”. Which can break encryption.

Simple quantum computers already exist, but it has been extremely challenging to build powerful versions of them. That’s because the quantum world is so delicate; the slightest disturbances in the outside world, such as stray electrical signals, can cause a quantum computer to crash before it can perform useful calculations.

National Institute of Standards and Technology (NIST) public affairs specialist Chad Boutin interviewed Alexey Gorshkov, a NIST theorist at NIST / University of Maryland. Common Center for Quantum Information and Computing (QuICS) and Joint Quantum Institute, who works at the intersection of physical and computer research. His efforts help in the design of quantum computers, revealing what skills they might possess, and showing why we should all be excited about their creation.

We all hear about quantum computers and how many research groups around the world are trying to help build them. What has your theoretical work helped to explain about what they can do and how?

I’m working on ideas for quantum hardware. Quantum computers will be different from the classic computers we all know, and they will use memory units called cubits. One thing I do is propose ideas for various qubit systems consisting of different materials, such as neutral atoms. I’m also talking about how to make logic gates, and how to connect kits to a large computer.

Another thing my group is doing is proposing quantum algorithms: software that can be run on a quantum computer. We also study large quantum systems and find out which ones promise to make useful computing faster than is possible with classic computers. So, our work covers a lot of ground, but there is a lot to do. You have this big, complicated animal in front of you and you are trying to tear it apart with whatever tools you have.

You focus on quantum systems. What are they?

I usually start by saying, on a very small scale the world obeys quantum mechanics. People know about atoms and electrons, which are small quantum systems. Compared to the large objects we know, they are strange because they can be in two seemingly incompatible states at the same time, like particles in two places at the same time. The way these systems work at first is weird, but you get to know them.

Large systems, consisting of a mass of atoms, are different from individual particles. Those weird quantum effects we want to take advantage of are hard to keep in larger systems. Let’s say you have one atom that works as a quantum memory piece. A small perturbation such as a nearby magnetic field has a chance of causing the atom to lose its information. But if you have 500 atoms working together, that disturbance is 500 times more likely to cause a problem. That’s why classical physics has worked so well for so many years: Because classical effects override strange quantum effects so easily, usually classical physics is enough for us to understand the great objects we know from our daily lives.

What we do is try to understand and build large quantum systems that “stay quantum” – something we specialists call “coherent” – even when they are large. We want to combine many ingredients, such as 300 quits, and yet make sure that the environment does not spoil the quantum effects we want to take advantage of. Large coherent systems that are not killed by the environment are difficult to create or even simulate on a classical computer, but coherence is also what will make large systems as powerful as quantum computers.

What is convincing about a large quantum system?

One of the first incentives to try to understand large quantum systems is possible technological applications. So far quantum computers have done nothing useful, but people think they will do it very soon and it is very interesting. Quantum internet would be a secure internet, and it would also allow you to connect many quantum computers to make them more powerful. I am fascinated by these possibilities.

It is also fascinating because of its fundamental physics. You are trying to understand why this system does some fun things. I think a lot of scientists just enjoy doing that.

Why are you so interested in quantum research?

I got my first exposure to it after my young year in college. I quickly found that it has a great mix of math, physics, computer science, and interactions with experimenters. The intersection of all these fields is why it’s so fun. I like to see the relationships. You end up pulling an idea from one field and applying it to another and it becomes this beautiful thing.

Many people are worried that a quantum computer will be able to break all our encryption, revealing all our digitized secrets. What are some less worrying things they could do that excite you?

Before I get into what excites me, let me first say that it is important to remember that not all of our encryption will be broken. Some encryption protocols are based on mathematical problems that will be vulnerable to a quantum computer, but other protocols are not. NIST’s post-quantum cryptography project is working on encryption algorithms that could hinder quantum computing.

What excites me, many do! But here are some examples.

One thing we can do is simulate. We may be able to simulate really complicated things in chemistry, materials science, and nuclear physics. If you have a large complex chemical reaction and you want to find out how it happens, you need to be able to simulate a large molecule that has many electrons in a cloud around it. It’s a mess, and it’s hard to study. A quantum computer can basically answer these questions. So maybe you could use it to find a new drug.

Another possibility is to find better solutions to what are called classic optimization problems that give a lot of problems to classic computers. An example is, “What are more efficient ways to direct shipments in a complex supply chain network?” It is unclear whether quantum computers will be able to answer this question better than conventional computers, but there is hope.

Sequel to the previous question: If quantum computers are not built yet, how do we know anything about their capabilities?

We know – or think we know – the microscopic quantum theory on which quantities rely, so if you put these quantities together, we can describe their abilities mathematically, and that would tell us what quantum computers could do. It is a combination of mathematics, physics and computer science. You just use the equations and go to the city.

There are skeptics who say that there may be effects that we do not yet know that would destroy the ability of large systems to remain coherent. These skeptics are unlikely to be right, but the way to counter them is to do experiments on larger and larger quantum systems.

Are you pursuing a particular research goal? Any dreams you would like to realize someday, and why?

The main motivation is a quantum computer that does something useful. We live in an exciting time. But another incentive is just to have fun. As a kid in eighth grade, I would try to solve math problems for fun. I just couldn’t stop working on them. And while you’re having fun, you’re discovering things. The kinds of problems we solve now are just as fun and exciting for me.

After all, why NIST? Why is working at a measurement lab on this research so important?

Quantum is the heart of NIST, and its people are why. We have leading experimenters here including multiples Nobel laureates. NIST gives us the resources to do great science. And it is good to work for a public institution where society can be served.

In many ways, quantum computing came out of NIST and measurement: It came from trying to build better clocks. Dave WinelandThe work of ions is important here. Jun YeThe work of neutral atoms is also. Their work has led to the development of amazing control over ions and neutral atoms, and this is very important for quantum computing.

Measurement is at the heart of quantum computing. An exciting open question that many people are working on is how to measure the “quantum advantage,” as we call it. Suppose someone says, “This is a quantum computer, but how big is its advantage over a classic computer?” We propose how to measure that.

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