06 March 2019 Frontiers of Light Trapping in Nature Reviews

Topological solitons in a liquid crystal.

The review, published in Nature Reviews Physics, provides an update status on multidimensional trapping of light and matter. Soliton-like bound states — self-sustained localized packets of light or matter waves in nonlinear media — are a matter of intense study in several areas of physics, such as nonlinear photonics, Bose–Einstein condensates (BECs), plasmas, superconductors, semiconductors, magnetic materials, gravitation and cosmology, to name a few. Experimental observations of solitons have been reported in many systems, but in their vast majority only in 1D settings.

Observing 2D and 3D soliton geometries could open a window to a new variety of new physical phenomena. However, this remains a long-standing challenge since the simplest fundamental solutions of the corresponding nonlinear wave equations are often subject to very strong instabilities. Thus, the central task so far has been to stabilize multidimensional states, and bearing this in mind, numerous approaches have been proposed over the years, approaches that have made far more advances in the theoretical field than with experimental demonstrations.

In this paper in Nature Reviews Physics, ICFO researchers Yaroslav Kartashov and Prof. and Director of ICFO Lluis Torner, Gregory Astrakharchik from the UPC and Boris Malomed from the Tel Aviv University, provide an overview of the recent theoretical and experimental progress that has been made in the creation of dynamically stable, multidimensional, soliton-like states, with a focus on optical materials, matter-wave condensates and ultradilute quantum liquids, liquid crystals and ferrofluids.

The review aims to bridge different communities to promote the exchange of ideas and to facilitate the implementation of concepts, which were originally developed for a specific physical setting and that now aim for completely different settings. The motivation of such attempt is harnessing the opportunities offered by multidimensional settings for the creation of localized states with rich internal structures that are not possible in 1D geometries.

The review highlights the recent breakthrough regarding the experimental creation of quantum droplets, which are stable in 2D and 3D geometries and that owe their stability to quantum fluctuations and are topic in which ICFO Prof Leticia Tarruell and co-workers have made important landmark contributions recently.

The Review stresses that over the past decade, photonic settings and BECs in optical lattices proved to be powerful tools to mimic the behaviour of other physical systems that are much harder to access experimentally. Thus, the research on the formation of multidimensional self-trapped states should be seen from a similar perspective, hence its fundamental and far-reaching importance.