The following is a Q&A originally published on Taking Measure, the official blog of the National Institute of Standards and Technology (NIST). Photo credit: NIST.
As the rise of quantum computers becomes the subject of more and more news articles — especially those that prophesy these devices’ ability to crack the encryption that protects secure messages, such as our bank transfers — it’s illuminating to speak with one of the quantum experts who is actually developing the ideas behind these as-yet-unrealized machines. Whereas 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 simultaneously, enabling them to perform certain functions exponentially faster, such as trying out the different “keys” that 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 tiniest disturbances from the outside world, such as stray electrical signals, can cause a quantum computer to crash before it can carry out 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 Joint Quantum Institute, who works at the intersection of physics and computer science research. His efforts are helping in the design of quantum computers, revealing what capabilities they might possess, and showing why we all should 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 clarify about 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 they will use memory units called qubits. One thing I do is propose ideas for various qubit systems made up of different materials, such as neutral atoms. I also talk about how to make logic gates, and how to connect qubits into a big computer.
Another thing my group does is propose quantum algorithms: software that one can potentially run on a quantum computer. We also study large quantum systems and figure out which ones have promise for doing useful computations faster than is possible with classical computers. So, our work covers a lot of ground, but there’s a lot to do. You have this big, complicated beast in front of you and you’re trying to chip away at it with whatever tools you have.
You focus on quantum systems. What are they?
I usually start by saying, at very small scales the world obeys quantum mechanics. People know about atoms and electrons, which are small quantum systems. Compared to the big 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 weird at first, but you get to know them.
Large systems, made up of a bunch of atoms, are different from individual particles. Those weird quantum effects we want to harness are hard to maintain in bigger systems. Let’s say you have one atom that’s working as a quantum memory bit. A small disturbance like 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 as likely to cause a problem. That’s why classical physics worked well enough for so many years: Because classical effects overwhelm weird quantum effects so easily, usually classical physics is enough for us to understand the big objects we know from our everyday life.
What we’re 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 lots of ingredients, say 300 qubits, and yet ensure that the environment doesn’t mess up the quantum effects we want to harness. Large coherent systems that are not killed by the environment are hard to create or even simulate on a classical computer, but coherence is also what will make the large systems powerful as quantum computers.
What is compelling about a large quantum system?
One of the first motivations for trying to understand large quantum systems is potential technological applications. So far 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 also would allow you to connect many quantum computers to make them more powerful. I’m fascinated by these possibilities.
It’s also fascinating because of fundamental physics. You try to understand why this system does some funny stuff. 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 junior year in college. I quickly found it has a great mix of math, physics, computer science and interactions with experimentalists. The intersection of all these fields is why it’s so much fun. I like seeing the connections. You end up pulling an idea from one field and applying it to another and it becomes this beautiful thing.
Lots of people worry that a quantum computer will be able to break all our encryption, revealing all our digitized secrets. What are some less worrying things they might be able to do that excite you?
Before I get into what excites me, let me say first that it’s important to remember that not all of our encryption will break. Some encryption protocols are based on math problems that will be vulnerable to a quantum computer, but other protocols aren’t. NIST’s post-quantum cryptography project is working on encryption algorithms that could foil a quantum computer.
As for what excites me, lots does! 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’s taking place, you have to be able to simulate a big 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 possibility is finding better solutions to what are called classical optimization problems, which give classical computers a lot of trouble. An example is, “What are more efficient ways to direct shipments in a complex supply chain network?” It’s not clear whether quantum computers will be able to answer this question any better than classical computers, but there’s hope.
A follow-up to the previous question: If quantum computers aren’t actually built yet, how do we know anything about their abilities?
We know — or think we know — the microscopic quantum theory that qubits rely on, so if you put these qubits together, we can describe their capabilities mathematically, and that would tell us what quantum computers might be able to do. It’s a combination of math, physics and computer science. You just use the equations and go to town.
There are skeptics who say that there might be effects we don’t know about yet that would destroy the ability of large systems to remain coherent. It’s unlikely that these skeptics are right, but the way to disprove them is to run experiments on larger and larger quantum systems.
Are you chasing a particular research goal? Any dreams you’d like to realize someday, and why?
The main motivation is a quantum computer that does something useful. We’re living in an exciting time. But another motivation is just having 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 as you have fun, you discover things. The types of problems we are solving now are just as fun and exciting to me.
Lastly, why NIST? Why is working at a measurement lab on this research so important?
Quantum is at the heart of NIST, and its people are why. We have top experimentalists here including multiple 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 clocks. Dave Wineland’s work with ions is important here. Jun Ye’s work with neutral atoms is too. Their 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 lots 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 just how big is its advantage over a classical computer?” We’re proposing how to measure that.