Ignacio Cirac: "Quantum computers will accelerate the learning capacity of artificial intelligence"

The laws of physics that explain how the world we see and surrounds us works stop being valid when we scrutinize everything that happens in the microscopic realm. There, the most elementary particles that make up matter, such as atoms, but also smaller ones, such as electrons, have very exotic properties that challenge all intuition and seem almost impossible, as exemplified by Schrödinger's famous cat, alive and dead at the same time inside a box until he observes it.

The theory that explains the rules of this particle world is quantum mechanics or physics and has allowed us to make extraordinary advances, such as electronics: from computers to mobile phones, LED lights, solar panels and medical equipment in hospitals, among others.

The physicist Ignacio Cirac (Manresa, 1965) is one of the world's leading experts in this field. And his name is heard every year in the pools for the Nobel Prize in Physics for his major contributions, especially in quantum computing. His theoretical work has opened new avenues of experimental research in areas such as materials science, high-energy physics, chemistry and cryptography, which has earned him numerous awards, such as the Prince of Asturias and the prestigious Wolf, as well as the Max Planck Medal. Now his research focuses on how to use quantum physics to communicate more efficiently and securely, and at increasingly greater distances.

Since 2001 he has been the director of the theoretical division of the Max Planck Institute for Quantum Optics in Garching (Munich, Germany) and is a guest researcher and scientific advisor at the Institute of Photonic Sciences (ICFO), located in Castelldefels. Last week he visited Barcelona to participate in the debate programRadical Science, curated by physicist and science journalist Toni Pou, ARA collaborator, at the Centre for Contemporary Culture of Barcelona (CCCB).

UNESCO has declared in 2025 theInternational Year of Quantum Science and Technology. Because?

— Firstly, because it has been a hundred years since the theory was developed that has allowed us to understand how matter works at a microscopic scale and that has led us to design the electronic systems that we have in almost all the devices we use every day: semiconductor materials, LEDs, lasers. We call this the first quantum revolution, and with this international year we pay tribute to it. But, in addition, we want to celebrate that in recent years quantum technologies have made great progress and have generated many expectations, even making headlines in the media and appearing in political speeches.

So, are we already in the second quantum revolution?

— It hasn't arrived yet. This second revolution is based on trying to explain other laws of quantum physics that we knew before, but that we couldn't exploit. And they are the strangest of all, because they are the least intuitive.

Nothing in quantum seems intuitive!

— Yes, but there are different levels. As with planets, electrons can only move and be in certain orbits, while others are forbidden, and this can challenge our imagination. But if I say that an object has no defined where it will be, that it does not even know where it is, nor can it know, that completely defies intuition. And these are according to laws, stranger ones, that we have now managed to master in laboratories and that we want to use.

What will they allow?

— Above all, working with information. They will allow us to process it on computers in a somewhat different way than now. We will have communication systems based on quantum physics that will be much more secure than those we have today.

Will quantum computers be needed?

— That's right. Although we've been hearing about it for a long time, in recent years we've made substantial progress. If you have a few million euros, you can now buy one. And not only that, but you can invest, buy shares on the market. Although right now they are machines that don't solve much, they do more than the ones we had twenty years ago, of course. Back then they were small prototypes that basically demonstrated the operating principle. In that time they have been developed further and have increased in size. However, they are still far from the quantum computer that we want to have in the future.

Do they do anything better than today's computers or supercomputers?

— At the moment, they are dedicated to solving academic problems. In 2019, Google announced that it had achieved quantum supremacy, news that went around the world. They invented an academic problem to obtain random numbers following specific guidelines. With a quantum computer, the problem could be solved in a matter of minutes, while with a normal computer, obtaining these random numbers would take millions and millions and millions of years, surely more than the age of the Universe. In the future, they will also be able to decrypt messages. Thus, if you buy something with your credit card and I have a quantum computer, I will be able to find out what your card number is, something that we cannot do with current computers and that is why they are secure transactions.

But then they will create a security problem!

Yes, indeed. But on the other hand, quantum communication technologies, not computers, allow messages to be securely encrypted, even against quantum computers themselves. In the end, we have no gains in this area, because quantum computers damage something that we must also fix with quantum physics. But there are more examples of applications, such as scientific calculations. Scientists want to solve many problems and we cannot do so due to lack of computing power. Quantum computers will allow us to solve them. Also problems of how materials behave at very low temperatures, issues related to theories of gravity, quantum many-body theories. Or in the design of materials or products that come from a chemical reaction, such as a drug, for which very complicated calculations are needed for a normal computer that quantum computers can easily do. Or problems related to industrial optimization processes. Of course, there are also some questions of artificial intelligence, because quantum computers can speed up how AI learns. But perhaps the clearest application of quantum computers that we know of is trying to simulate complex quantum processes.

It's a bit of a paradox.

— True. If we have a problem that we need to describe with quantum physics, such as those in chemistry or materials, they are difficult or impossible to solve with supercomputers. Quantum simulation uses quantum computers to simulate what will happen in the future, to make predictions with them, because in these areas there are problems that require the rules of quantum physics. In fact, many of the discoveries that have been made with quantum simulations have led to research with classical computers and have allowed the development of better algorithms for classical computers. The most important thing is that all these are just some examples that we now know of the many applications that they will have and that we are not even able to imagine now.

How do quantum computers work?

— It's not that they are faster than classical computers, but that they use a different way of solving problems and processing information. It is based on the laws of quantum physics, it works with what we call quantum superpositions, which is something that does not exist in the macroscopic world, only in the microscopic: the same object can do several things at once. So, quantum computers can solve several tasks at once, work in parallel and that allows us to speed up. But while they are working and performing these operations we cannot look at them, because otherwise they will stop working. And for that reason, it is necessary to isolate them very well, which is the great battle today. We need to build quantum computers that are large enough, but that are well isolated so that we can exploit them.

Where are they being built?

— Some companies in the US, China and also Europe are building small prototypes. Each one uses a different technology and we still don't know which one will prevail. But this is important, because in this race to build quantum computers many technologies will be developed that may be even more important than the quantum computers themselves. The entire ecosystem that is created in a place is more important than building the computer, which is why it is crucial that cities like Barcelona start to develop Start-ups and interested industry.

The Barcelona Supercomputing Center will have one of the first quantum computers in Europe.

— Yes, in Catalonia and Spain, in Europe in general, there is a significant investment in quantum technologies. In Germany, where I live, a lot of funding is being injected. However, it is difficult to compete with our colleagues in China, where funding is enormous, on a larger scale, or with the Americans, because they have a very powerful industry that we do not have in Europe, especially in terms of information technology. It is very positive that an initiative such as the Quantum Spain project has been launched, where the ICFO plays a leading role and stands out in quantum communications. Other Catalan institutions, recognised throughout the world, are also playing a crucial role and are leading the way in some quantum technologies. This is impressive, that a country that does not have a solid industry is leading the way. It is also very positive that Catalan politicians are convinced of the importance of quantum technologies and support their development.

Is it important for Catalonia, for Europe, to develop its own quantum computer?

— Let us imagine that one were built in a country that is not friendly to the West. This computer would be able to decipher our secret messages, create better drugs, better materials; it would generate many patents; it would probably revolutionize industry, optimize its processes better, and have an economic and even military advantage. This, which is an exaggeration, would be a problem.