Photonics Initiative Seminar: Angel Rubio

Abstract – A central challenge in computational physics is the accurate modeling and control of quantum materials under the influence of light. Traditional approaches such as Time-Dependent Density Functional Theory (TDDFT) have enabled progress in simulating light-driven phenomena, but new frameworks are required to capture the effects of quantized electromagnetic fields on matter at equilibrium. In this context, Cavity Materials Engineering has emerged as a powerful paradigm, enabling ground-state modifications of materials by embedding them in optical cavities and leveraging vacuum fluctuations, rather than external driving or photon excitation. This “dark” regime departs from conventional polaritonic physics by targeting the material ground state directly. When coupled to intrinsic nonlinearities—such as anharmonic phonon modes or metastable phases—vacuum fluctuations can induce macroscopic changes in material properties, including superconductivity, magnetism, and structural transitions. The mechanism is conceptually similar to boson-mediated interactions in condensed matter, yet uniquely exploits the electromagnetic vacuum as the mediating field. To model these phenomena, we present the conceptual foundations of Quantum Electrodynamical Density Functional Theory (QEDFT)—a first-principles framework that seamlessly incorporates light-matter interactions into electronic structure theory. We will introduce its key theoretical principles and highlight recent applications demonstrating how cavity quantum electrodynamics can be used to predict and control emergent phases of quantum matter. This approach opens new frontiers in material design at the intersection of quantum optics and many-body physics.

• Engineering quantum materials with chiral optical cavities , H. Hübener, U. D. Giovannini, C. Schäfer, J. Andberger, M. Ruggenthaler, J. Faist, and A. Rubio Nature materials 20, 438-442 (2021)
• Quantum materials engineering by structured cavity vacuum fluctuations}\\H. Hübener, E. Vi\~nas Bostr\”om, M. Claassen, S. Latini, A. Rubio Mater. Quantum. Technol. {\bf 4} 023002 (2024) (link https://iopscience.iop.org/article/10.1088/2633-4356/ad4e8b/pdf)
• Cavity engineered phonon-mediated superconductivity in MgB2 from first principles quantum electrodynamics, I-T. Lu, Dongbin Shin, Mark Kamper Svendsen, Hannes Hübener, Umberto De Giovannini, Simone Latini, Michael Ruggenthaler, Angel Rubio, Proceedings of the National Academy of Science USA (PNAS) 121, e2415061121 (2024) 
• Controlling the magnetic state of the proximate quantum spin liquid α-RuCl3 with an optical cavity,  Emil Vinas Boström, Adithya Sriram, Martin Claassen, Angel Rubio, npj Computational Materials 9, 202 (2023)
• The ferroelectric photo ground state of SrTiO3: Cavity materials engineering, S. Latini, D. Shin, S. A. Sato, C. Schäfer, U. D. Giovannini, H. Hübener, and A. Rubio PNAS 118, e2105618118 (2021)
• Understanding polaritonic chemistry from ab initio quantum electrodynamics, M. Ruggenthaler, D. Sidler, A. Rubio, Chemical Reviews 123, 11191 (2023)
• Theory of quantum light-matter interaction in cavities: Extended systems and the long wavelength approximation, Mark Kamper Svendsen, Michael Ruggenthaler, Hannes Hübener, Christian Schäfer, Martin Eckstein, Angel Rubio, Simone Latini  arXiv: arXiv:2312.17374
• Cavity Spectroscopy for Strongly Correlated Systems, Lukas Grunwald, Emil Viñas Boström, Mark Kamper Svendsen, Dante M. Kennes, Angel Rubio, arXiv:2410.21515

Bio – Prof. Angel Rubio received his PhD in Physics with honors from the University of Valladolid in 1991 where he did fundamental work on the structural and optical properties of metallic clusters. Then moved to a postdoctoral position at UC Berkeley-Physics (92-95) where he predicted a new type of boron-nitride nanotubes (PRB1994) triggering their ensuing experimental synthesis. Between 1994 and 2001 as Professor at UVA he started the ab initio materials research open-source project octopus used now by over 1000 groups worldwide. Diverse Professorships at École Polytechnique Paris, FU Berlin and Montpellier followed. In 2001 he moved as Chair of Condensed Matter Physics at UPV/EHU. There he engaged in highly successful work on modeling of excited-state properties of materials and nanostructures setting the foundations of modern theoretical spectroscopy (RMP2002). In August 2014 he accepted the position as Max Planck Director. There he has pioneered the development of quantum electrodynamical density functional theory (QEDFT), a novel theoretical framework for strong light-matter phenomena in chemistry and materials sciences (PNAS2015, Nat.Rev.Chem.2018). His work has been recognized by several awards, including the 2023 Spanish National Physics Prize “Blas Cabrera” 2018 Max Born medal and prize, 2016 Medal of the Spanish Royal Physical Society and the 2014 Premio Rey Jaime I for basic research, and more, and elected member of different academies, including the German Leopoldina Academy and Berlin-Brandenburgischen Akademie der Wissenschaften, the European Academy of Sciences, the Academia Europaea, and a foreign associate member of the National Academy of Sciences (USA).