What’s so good about quantum computing? A question and answer session with NIST theorist Alexey Gorshkov

Alexey Gorshkov poses in front of a whiteboard, holding a marker.

Alexey Gorshkov is a NIST theorist who works at the intersection of physics and computer science 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 crack the encryption that protects secure messages, like our bank transfers, it’s illuminating to talk to one of the quantum experts who is actually developing the ideas behind these unrealized machines. While ordinary computers run on data bits that can be 0 or 1, quantum computers run on bits, called qubits, that can be 0 and 1 simultaneously, allowing them to perform certain functions exponentially faster, such as testing different “keys”. ” which can break the encryption.

Simple quantum computers already exist, but building powerful versions of them has been extremely challenging. That’s because the quantum world is so delicate; the smallest disturbances from the outside world, such as stray electrical signals, can cause a quantum computer to crash before it can perform any 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. Joint Center for Quantum Information and Computing (QuICS) and Joint Quantum Institute, which works at the intersection of physics and computer science research. His efforts are aiding in the design of quantum computers, revealing what capabilities 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 helped clarify your theoretical work on what they can do and how?

I work on ideas for quantum computer hardware. Quantum computers will be different from the classical computers we all know and will use memory units called qubits. One thing I do is come up with ideas for various qubit systems made of different materials, like neutral atoms. I also talk about how to make logic gates and how to connect qubits to a big computer.

Another thing my group does is come up with quantum algorithms: software that you can potentially run on a quantum computer. We also study large quantum systems and find out which ones show promise for performing useful calculations faster than is possible with classical computers. So our work covers a lot of ground, but there is a lot to do. You have this big, complicated beast in front of you and you’re trying to undermine it with the tools you have.

You focus on quantum systems. What are they?

I usually start by saying that, on very small scales, 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 peculiar in that they can be in two seemingly incompatible states at once, like particles being in two places at the same time. The way these systems work is strange at first, but you get to know them.

Large systems, made up of a group of atoms, are different from individual particles. Those weird quantum effects we want to take advantage of are hard to maintain in larger systems. Let’s say you have an atom that works like a bit of quantum memory. A small disturbance, such as a nearby magnetic field, has the potential to cause 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 worked well enough for so many years: because classical effects outweigh weird quantum effects so easily, classical physics is usually enough for us to understand the large objects we know from our lives. daily life.

What we are doing is trying to understand and build large quantum systems that “stay quantum,” something we specialists call “coherent,” even when they are large. We want to combine a lot of ingredients, say 300 qubits, and still make sure the environment doesn’t mess up the quantum effects we want to harness. 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 compelling about a large quantum system?

One of the first motivations to try to understand large quantum systems is the possible technological applications. Until now, quantum computers haven’t done anything useful, but people think they will very soon and it’s very interesting. A 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’s also fascinating because of the fundamental physics. You try to understand why this system does some weird things. I think a lot of scientists just enjoy doing that.

Why are you personally so interested in quantum research?

I had my first exposure to it after my junior year in college. I quickly discovered that he has a great mix of math, physics, computer science, and interactions with experimenters. The intersection of all these fields is why he is so much fun. I like to see the connections. You end up taking an idea from one field and applying it to another and it becomes something beautiful.

Many people worry that a quantum computer could break all of our encryption, revealing all of our digitized secrets. What are some less worrying things that might make you excited?

Before I get into what gets me excited, let me first say that it’s important to remember that not all of our encryption will break. 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 thwart a quantum computer.

As for what excites me, a lot! But here are a couple of examples.

One thing we can do is simulation. We might be able to simulate really complicated things in chemistry, materials science, and nuclear physics. If you have a big complex chemical reaction and you want to figure out how it works, you need to be able to simulate a big molecule that has a lot of electrons in a cloud around it. It’s a mess, and it’s hard to study. In principle, a quantum computer can answer these questions. So maybe you could use it to find a new drug.

Another possibility is to find better solutions to so-called classical optimization problems, which give classical computers many problems. An example is: “What are the most efficient ways to direct shipments in a complex supply chain network?” It is not clear whether quantum computers will be able to answer this question better than classical computers, but there is hope.

A continuation of the previous question: if quantum computers are not yet built, how do we know anything about their abilities?

We know, or think we know, the microscopic quantum theory that qubits are based on, so if you put these qubits together, we can describe their capabilities mathematically, and that would tell us what quantum computers could do. It is a combination of mathematics, physics and computer science. Just use the equations and go to town.

There are skeptics who say there could be effects we don’t yet know about that would destroy the ability of large systems to remain coherent. These skeptics are unlikely to be right, but the way to refute them is to conduct experiments on larger and larger quantum systems.

Do you pursue a particular research objective? Do you have a dream that you would like to realize one day, and why?

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

Finally, why NIST? Why is it so important to work in a measurement laboratory in this research?

Quantum is at the heart of NIST, and its people are why. We have the best experimenters here, including multiple Nobel Prizes. NIST gives us the resources to do great science. And it is good to work for a public institution, where you can serve society.

In many ways, quantum computing grew out of NIST and measurement: It grew out of trying to build better clocks. dave land of wine‘s work with ions is important here. jun yeThe work of with neutral atoms is also. His work 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 a lot of people are working on is how to measure the “quantum advantage,” as we call it. Suppose someone says, “Here is a quantum computer, but what is its advantage over a classical computer?” We are proposing how to measure that.

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