Wave Front Engineering in Systems with Loss and Disorder

Progress in photonics has traditionally been linked to technological advances in fabricating ever more complex optical devices. In this multi-faceted endeavor to create arbitrary dielectric structures, two components that have remained largely untapped are loss and disorder. This is because of the prevailing view that the mere absorption of radiation by the loss and the seemingly random scattering induced by a disordered material are purely detrimental and thus only of academic, but not of any practical interest. Recent theoretical insights and the emerging experimental possibilities to shape and detect very complicated light fields are currently, however, overturning this traditional way of thinking. The goal of this project will be to leverage this paradigm shift by exploring promising concepts for mitigating the adverse influences of loss and disorder and for turning them to an advantage. Based on preliminary results, we aim to build the first "random anti-laser" a disordered and dissipative structure that perfectly absorbs all of an incoming radiation field. In parallel, we will devise a novel framework for focusing radiation on a target embedded in a disordered medium and for manipulating this target. Our approach to cope with the presence of disorder will build on the recent breakthrough to characterize a highly complex medium by measuring its scattering matrix. This set of parameters characterizes how any possible input wave impinging on a system gets scattered into a certain output. To extract these relevant data sets we plan to carry out microwave experiments together with our colleagues in Nice (France). Having the full scattering matrix available will then allow us to calculate how the wave fields have to look like that get perfectly absorbed by the medium or focus inside of it. These special wave states will then be generated in the experiment to test the viability of such novel protocols and how well they work also in a real-world experiment. As outlined in our proposal, the availability of the scattering matrix in a dissipative and disordered medium will allow us to explore also a whole plethora of other research directions - both from a theoretical and an experimental point of view. The two partners involved in this project proposal - the theory group of Stefan ROTTER in Vienna and the experimental group of Waves in Complex Systems (Ulrich KUHL, Fabrice MORTESSAGNE, and Olivier LEGRAND) in Nice - already have a proven track record of successful collaboration as indicated by several joint papers. The ground work that has already been laid in past interactions between the groups will be a solid basis for the execution of this joint project.

Project Summary: WAVELAND (2019-2023) The WAVELAND project, initiated on September 1, 2019, has made significant advances in the field of wavefront engineering in systems with loss and disorder. At its core, the project focuses on controlling waves in complex environments, with significant implications for optical, microwave and ultrasound technologies. Key achievements of WAVELAND were implemented in a collaboration with Allard Mosk's experimental group at Utrecht University. This partnership resulted in significant publications, including a study on shaping laser beams to maximize information extraction about specific system parameters, published in Nature Physics. Another relevant work introduced scattering-invariant modes, which produce consistent output patterns through both scattering media and free space, offering potential for probing highly scattering materials. This study was published in Nature Photonics. The project also explored non-Hermitian media to control light propagation. This research demonstrated that adding gain and loss to disordered media could suppress scattering, with findings published in Optica and Physical Review A. These innovations have potential applications in optical communication and computing. In WAVELAND, we further developed new wavefront shaping techniques to enhance optical trapping and manipulation, and we theoretically demonstrated the periodic exchange of excitations between two quantum emitters, illustrating strong multi-mode coupling. These achievements highlight the project's contributions to fundamental physics. In terms of recognition, the project's work has been widely acknowledged. Two publications were among the top 10 physics breakthroughs of the year by Physics World. The project's research has been featured in numerous high-impact journals, including Nature, Science, and Physical Review Letters. Additionally, the project received significant media attention (such as in Physics Today, New Scientist, Scientific American, etc.). The WAVELAND team also fostered international collaborations, notably with Ulf Leonhardt from the Weizmann Institute of Science. His visits in Vienna led to joint publications on quantum vacuum forces and wavefront shaping with quantum light. These collaborations enriched the project's research and expanded its scope. The project has not only advanced scientific knowledge but also supported the career development of its researchers. For example, PhD student Matthias Kühmayer transitioned to a role in the semiconductor industry, while Lukas Rachbauer became a data scientist in the pharmaceutical sector. Postdoctoral researcher Ivor Kresic obtained a permanent research position at the Institute of Physics in Zagreb (Croatia). These successes demonstrate the project's contribution to workforce development. Also a patent application was filed together on a new matrix imaging method with collaborators in France (including an exploitation agreement with an international medical company). Overall, the WAVELAND project has made substantial contributions to wavefront engineering, resulting in numerous high-impact publications and significant scientific breakthroughs. The project's success is marked by strong international collaborations, wide media coverage, and practical applications in medical technologies.