Martí Perarnau Llobet, physicist: ‘We understand the quantum world well and the laws to describe it work wonderfully’

Martí Perarnau Llobet, 36, is researching the extravagant and hidden world that hides the answers to what reality is, beyond what we perceive and to which we apply the classical laws of physics to manage the world. Winner of the Young Researcher Award in Theoretical Physics, awarded by the BBVA Foundation and the Royal Spanish Society of Physics, he works with the Ramón y Cajal program at the Autonomous University of Barcelona, unraveling the behavior of open quantum systems, those that are not isolated from their environment. This field will facilitate computing with lower energy consumption and the manufacture of extremely precise sensors, a great hope for personalized medicine, among other fields.

Question. Multinationals such as Microsoft, Google and IBM have announced significant advances in quantum computing. Is the hype around this technology justified?

Answer. There are great expectations surrounding quantum computing due to its immense potential. A quantum computer can be more powerful at performing certain calculations than all the computers on the planet working at the same time. But they are still very imperfect and this means that, although it may seem like you have a very powerful machine, the reality is that it is not that powerful. But the path to getting one is already interesting in itself, because it allows us to improve the control of quantum systems and, at the same time, provides new ideas to improve conventional computers. What is undeniable is that it is leading to great scientific and technological progress.

Q. What is an open quantum system?

A. It is a system that is in contact with an environment, which is not isolated. This is a condition of almost all systems. If you have an atom in a vacuum, you could say that there is no environment, but there is; when you put energy into it, it interacts with the vacuum and the energy is lost in the form of a photon. The environment is there and quantum systems are susceptible to its presence. This is very important because it allows us to understand, for example, decoherence, why we go from a quantum world where there are superpositions to our reality, where things do not exist in two places at the same time. Open systems are very important for our understanding of the transition from the quantum world to the classical world. And also in practice because, if we want to improve quantum computers, we have to understand the interaction with the environment very well.

Q. Is your research a bridge between the quantum and classical worlds, between the laboratory and the everyday environment?

A. We understand the quantum world well and we have laws to describe it that work wonderfully, but it is true that it is very un-intuitive and, conceptually, really shocking and disruptive. What we do is relevant to exploit quantum phenomena that occur under very ideal conditions, understand them in more realistic situations and describe that transition.

Q. Can quantum phenomena be controlled in open environments?

A. What we can do is understand them and look for efficient ways to describe the environment to use it to our advantage. There are some quantum states with a strong interaction with the environment and they lose energy very quickly, but there are others that practically do not do so, that are like protected, and this, for example, can be very relevant for quantum computing. Understanding the physics of open systems helps us find ways to use it to our advantage.

Q. In practice, what can we achieve by understanding an open quantum system?

A. An important example is found in quantum metrology, which seeks to use quantum phenomena to improve the precision of measurements. In this field, quantum sensors are being developed that, even though they are open to the environment, can be very useful for measuring very small variations in physical magnitudes, such as a magnetic field or temperature. Today, atomic magnetometers can already be used to measure, in a very non-invasive way, magnetic fields that occur in the brain. Another possible application would be in cells, to measure temperature and its variations inside them.

Q. What is the main challenge?

A. Apart from quantum metrology, I also work on quantum thermodynamics, which seeks to understand the origin of irreversibility, of dissipation, why energy degrades into heat. A challenge in this field, which has so far been very theoretical, would be to find applications, to use these theoretical ideas about our understanding of thermodynamics at this quantum scale to, for example, develop new ways of computing with much lower energy consumption.

Q. How do you do research? What is a quantum laboratory like?

A. A quantum lab can be a really impressive thing, however, as a theoretical physicist my office is much more down to earth. Most of my work can be done with pen and paper, also through computer simulations. We also use the whiteboard a lot, to discuss possible ideas or calculations and projects – science is a very collaborative thing.

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