Alexey Gorshkov is a NIST theorist working at the intersection of physics and computer science research.
Credit: NIST
As the advent 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, such as our bank transfers – it’s enlightening to talk to one of the quantum experts who is 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 qubits – that can be 0 and 1 at the same time, enabling them to perform certain functions exponentially faster, such as trying the various “keys” that can break encryption.
Simple quantum computers already exist, but building powerful versions of them has been extremely challenging. It’s because the quantum world is so delicate; the slightest disturbance from the outside world, such as corrupted 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’s Joint Center for Quantum Information and Computer Science (QuICS) and the Joint Quantum Institute, who works at the intersection of physics and computer science research. His efforts help with the design of quantum computers, reveal what properties they can possess, and show 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 clarify what they can and how?
I’m working on ideas for quantum computer hardware. Quantum computers will be different from the classic computers we all know and they will use memory devices called qubits. One thing I do is suggest ideas for different qubit systems that are made up of different materials, such as neutral atoms. I’m also talking about how to make logical ports and how to connect qubits to a large computer.
Another thing my group does is suggest quantum algorithms: software that one could potentially run on a quantum computer. We also study large quantum systems and find out which ones promise to do useful calculations faster than is possible with classic computers. So our work covers a lot, but there is a lot to do. You have this big, complicated beast in front of you and you’re trying to grab it with whatever tool you have.
You focus on quantum systems. What are they?
I tend to 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 because they can be in two seemingly incompatible states at once, such as 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 consisting of a bunch of atoms are different from individual particles. The strange quantum effects we want to exploit are difficult to maintain in larger systems. Let’s say you have an atom that acts as a quantum memory bit. A small disturbance such as a nearby magnetic field has a chance of causing the atom to lose its information. However, if you have 500 atoms working together, it is 500 times as likely that the disturbance is causing a problem. This is why classical physics worked well enough for so many years: Because classical effects so easily overwhelm strange quantum effects, classical physics is usually enough for us to understand the great objects we know from our everyday lives.
What we do is try to understand and build large quantum systems that “remain quantum” – something we specialists call “coherent” – even when they are large. We will combine lots of ingredients, e.g. 300 qubits, and yet ensure that the environment does not destroy the quantum effects we want to exploit. Large cohesive systems that are not killed by the environment are difficult to create or even simulate on a classic computer, but coherence is also what will make the large systems powerful as quantum computers.
What is convincing about a large quantum system?
One of the first motives for trying to understand large quantum systems is potential technological applications. So far, quantum computers have not done anything useful, but people think they will very soon and that is 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 is also fascinating because of basic physics. You’re trying to understand why this system does some fun things. I think a lot of scientists just enjoy doing that.
Why are you personally so interested in quantum research?
I got my first exposure to it after my teenage years in college. I quickly found out that it has an amazing mix of math, physics, computer science, and interactions with experiments. The intersection of all these fields is the reason why it’s so much fun. I like to see the connections. You end up pulling an idea from one field and applying it to another, and it becomes this beautiful thing.
Many people worry that a quantum computer will be able to break all of our encryption and reveal all of our digitized secrets. What are some less worrying things they might be doing 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 breaks. 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 works on encryption algorithms that can prevent a quantum computer.
What excites me, many do! But here are a few examples.
One thing we can do is simulation. 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 figure out how it goes, you need to be able to simulate a large molecule that has lots of electrons in a cloud around it. It’s a mess and it’s hard to study. A quantum computer can, in principle, answer these questions. So maybe you could use it to find a new drug.
Another option is to find better solutions to what are called classic optimization problems, which give classic computers many problems. An example is, “What are more efficient ways to route 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 follow-up to the previous question: If quantum computers have not actually been built yet, how do we know anything about their capabilities?
We know – or think we know – the microscopic quantum theory that qubits depend on, so if you put these qubits together, we can describe their abilities mathematically, and that would tell us what quantum computers might be capable of. 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 about and that would destroy the ability of large systems to remain coherent. These skeptics are unlikely to be right, but the way to disprove them is to run experiments on larger and larger quantum systems.
Are you pursuing a specific research goal? Some dreams 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 eighth grade, I would try to solve math problems for fun. I just could not help but work on them. And while you’re having fun, you’re discovering things. The types of problems we solve now are just as fun and exciting for me.
Finally, why NIST? Why is it so important to work in a measurement lab with this research?
Quantum is the core of NIST and its people are therefore. We have top experimentalists here, including several Nobel laureates. NIST gives us the resources to do great science. And it’s good to work for a public institution where you can serve society.
In many ways, quantum computing came out of NIST and measurement: It came out of trying to build better watches. Dave Wineland’s work with ions is important here. Jun Yes work with neutral atoms is also. Their work led to the development of amazing control over ions and neutral atoms, and this is very important for quantum computation.
Measurement is the core of quantum computing. An intriguing open question that many people are working on is how to measure the “quantum advantage,” as we call it. Suppose someone says, “Here’s a quantum computer, but how big is its advantage over a classic computer?” We suggest how to measure it.
