2024 Joseph Thomson Medal and Prize

Professor Janne Ruostekoski has made pioneering and long-lasting theoretical contributions that have profoundly reshaped our fundamental understanding of cooperative interactions between light and atomic ensembles. Thanks to this work, we now understand how the collective optical response of cold-atom ensembles and trapped atomic arrays differs drastically from the conventional response of optical media experiencing dissipation or thermal motion, as encountered in thermal atomic vapours and conventional solid-state systems. The observable signatures of these collective phenomena deviate dramatically from the predictions by standard continuous media electrodynamics and have been verified in multiple dedicated experiments. 
 
These contributions have initiated and stimulated significant theoretical and experimental research, and Ruostekoski has actively collaborated with leading experimentalists. In a groundbreaking application to utilise and harness these collective effects, Ruostekoski has pioneered the studies of atomic planar arrays cooperatively responding to light, showcasing their potential as quantum metasurfaces for manipulating and controlling light. As a result of these endeavours, light-manipulating atomic planar arrays have emerged as a forefront research area in quantum optics of atoms, with high-profile experimental demonstrations including a single atomic layer mirror and transmission resonance linewidth narrowing below the fundamental quantum limit of a single atom. 

In the exploration of interactions of atoms with light, Ruostekoski has pioneered powerful methods for utilising light in controlled engineering of topologically non-trivial defects, textures and energy landscapes for atoms. This work has not only inspired experimentalists and theorists within the atomic physics community but has also reached into photonics, and solid-state and elementary particle physics communities. 

This framework of cooperative interactions between light and atomic ensembles has enabled Ruostekoski to extend the atomic concepts to universal settings, involving, for example, nanofabricated circuits interacting with electromagnetic fields, in which case giant, spatially extended subradiance was demonstrated in collaboration with experimentalists. These methods form a general, widely adapted framework that sheds light on the emergence of macroscopic electrodynamics from microscopic principles at the atomic level.