Catching up with QSpec-NewMat: Novel tools to better understand materials phenomena When the QSpec-NewMat project ended in 2021, it had created and implemented a toolbox for complex materials. Two years later, the tools have contributed to the development of new and more efficient materials and technologies for quantum information processing and energy materials. Industrial Technologies © agsandrew/stock.adobe.com Funded by the European Research Council (ERC), the QSpec-NewMat project developed the toolbox by combining the principles of time-dependent density functional theory and quantum electrodynamics (QED). This led to a new approach called quantum electrodynamical density functional theory (QEDFT). The tools use light to understand and control quantum phenomena in complex systems in and out of equilibrium. QSpec-NewMat has continued its line of research by investigating cavity-QED physics of correlated light-matter states, such as integer and fractional quantum Hall states. “A particularly attractive direction here is enhancing superconductivity in an optical cavity,” states Angel Rubio, director of project coordinator Max Planck Institute for the Structure and Dynamics of Matter in Germany. “One of the most exciting aspects of cavity-QED mediated quantum phenomena occurs in the strong-light-matter coupling regime when the ‘light field’ is not provided by an external laser field, but by the vacuum fluctuations of the cavity.” This fact clearly differentiates cavity-QED physics from ordinary non-linear optical phenomena that are induced by a strong external field and inevitably involve excited and/or non-equilibrium states of matter. As a result, this has opened exciting new opportunities for studying the interaction of quantised light with quantum many-body systems. In addition, it has provided several intriguing predictions, including enhancing superconductivity, driving paraelectric-ferroelectric transitions in perovskites, inducing emergent topological phases, and controlling photochemical reactions (inhibit, steer and even catalyse a chemical process and energy transfer). One novel idea is cavity control of many-body interactions. By modifying the single-particle Hamiltonian through cavity matter coupling, one can select the relevant interaction terms and thus control the form of their effective interactions. Another interesting question is whether optical cavities can serve as platforms for solid-state realisation of concepts from high-energy physics and the realisation of new fermionic quasiparticles in cavities. “These advances in materials control rely on having a versatile and accurate first principles setting that incorporates all relevant degrees of freedom – photons, electrons, phonons and the environment – on equal footing,” Rubio concludes. “Thanks in part to ERC funding, the novel theoretical frameworks QEDFT and couple-cluster QED have been developed to meet this challenge.” Keywords QSpec-NewMat, quantum, material, complex material, quantum electrodynamics, quantum electrodynamical density functional theory, cavity, light
