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Beam Shifts: Analogies between light and matter waves
The law of specular reflection in geometrical optics is among the oldest laws known in physics. It does, however, only hold approximately when a real light beam (described as a spatially confined vector field) impinges on a real material surface. Compared to a specularly reflected reference, the reflected beam can be shifted and deflected in and out of the plane of incidence, with the deviation depending on the angle of incidence, the spin angular momentum (polarization), and the orbital angular momentum of the incident beam. Analogous effects also occur for matter waves, such as neutron beams, and in condensed matter physics, where a prominent example is the Spin Hall effect.
The aim of this workshop was to bring together researchers from the relevant communities to explore the interdependence and analogies of the different shift effects. How far do the analogies go, and which novel shift effects can be expected to be discovered in other systems like neutron and electron beams? An intriguing optical beam-shift effect which facilitated this discussion is the “Spin Hall effect of light”, which is a counterpart to the spin Hall effect in condensed-matter physics. Another example is the angular Goos-Hänchen shift, whose analogues for electrons and neutrons had not been considered prior to our workshop.
Through a series of outstanding tutorials, lectures, research talks, and lively discussions between the sessions we achieved a significant step towards a unified understanding of these shift effects. There is now a much improved awareness of their commonalities and important differences, which will stimulate further research in a variety of directions. For instance, the spin Hall effect in condensed matter comprises several subtle effects, some of which require the presence of a periodic potential and external fields. In the conventional setting of optical beam shifts these are not present, and it has been intensely discussed between the different communities how periodic photonic nanostructures offer an excellent testbed to study these analogies more closely. Furthermore, there are now plans to search for the angular Goos-Hänchen shift with neutrons. This workshop has served as a potent catalyst for new collaborations, and at least one joint publication is in preparation.
The first two days of the programme were deliberately intense, with tutorials and more specialized talks by experienced researchers, and flash talks from the more junior participants. In this way we identified a number of questions, which were then addressed in informal and moderated discussion sessions. The second part of the workshop featured no more than 4 talks per day and therefore left room for more extensive discussions. We also offered guided tours through four laboratories, which proved to be a great success as they connected the more abstract discussion from the talks with concrete experimental realizations. This format was met with great enthusiasm by the participants, which were ideally balanced between senior and junior researchers, as well in regard to representation of the relevant communities.
In short, the workshop was a complete success. The participants and scientific organizers wish to express their great appreciation for the work and support of the Lorentz Center. The organizers acknowledge financial support from the following organizations NWO, Leids Universiteits Funds, International Newton Fellowship and the Quantum Optics & Quantum Information Group at Leiden University.