Carlo Beenakker: narrative CV (2023)

I had the fortune to join the research laboratory of Philips Electronics at a time that the first experiments were finding quantum interference effects in semiconductor nanostructures. One such experiment was the discovery of the conductance quantization in a point contact. I was the theorist of the team that reported this discovery in 1988. This launched me into the wonderful quantum world, and keeps fascinating me to this day. My training as a theoretical physicist was in classical physics, so I felt a bit out of my comfort zone in the quantum world. I was not fluent in the language used by more experienced researchers, and felt a need to develop my own way to approach problems. Random matrices provided that different view point. The theory of random matrices originated from nuclear physics, where Wigner and Dyson had used it to describe scattering resonances of heavy nuclei. Scattering of electrons in nanostructures looked like a similar problem, although the energy scales were competely different. I had found a powerful tool that allowed me to solve problems that had resisted solution by more conventional methods of quantum theory.

Initially I stayed close to the type of scattering problems studied earlier in nuclear physics, but when I moved to superconducting systems an altogether different range of applications emerged. These involved the peculiar effect known as "Andreev reflection", where an electron is reflected from a superconductor as its antiparticle. I formulated a theory of Andreev reflection that expresses the conductance in terms of properties of the scattering matrix, which can be seen as the superconducting analogue of the Landauer formula of non-superconducting systems. With that formulation I could predict a wide range of physical effects, many of which have since been observed in the laboratory.

All of this was for "ordinary" electrons. When in 2005 massless electrons where discovered in graphene an entirely new world opened up. My discovery of "specular Andreev reflection" in graphene points to a unique property of this carbon monolayer. This research prepared me for the emergence of topological superconductors. These materials are characterized by a topological invariant which signals the presence of a Majorana fermion: a particle that is its own antiparticle. With my group of students we developed the random matrix theory of topological superconductivity. We identified a computational signature of Majorana fermions (the sign of the determinant of the reflection matrix) that is widely used as an efficient and reliable indicator.

Majorana fermions are not yet conclusively observed in the laboratory, but if they can be produced reliably, they could be a game changer for a quantum computer. Much of my research in the last decade has been devoted to the development of methods to create and manipulate Majorana fermions. The impact of this line of research is still open ended.

While conducting research with my students is the occupation I am most passionate about, I try to serve the community of physicists as best I can in other ways as well. I am in the leadership of a major national program in The Netherlands to develop quantum technology. I serve on the panel that evaluates grant proposals for the European Research Council. I am involved in a variety of editorial activities, both in traditional journals (Science, PRX Quantum) and in community-run initiatives (Quantum, SciPost).