LMI Seminar: Self-trapped optical vortices and quantum droplets: Siblings in the soliton family

Topic: LMI Seminar - Boris Malomed

Meeting ID: 859 8160 3510

Abstract:

In the course of the past 25 years, several new quantum states of matter have been created in ultracold gases, starting from the celebrated Bose-Einstein condensates (BECs). A recent addition to the set  is provided by quantum droplets (QDs), composed of atomic waves in two-component BECs. This is an extension of BEC beyond the limits of the usual mean-field (quasi-classical) setting, with the action of quantum fluctuations (the Lee-Huang-Yang (LHY) effect) leading to drastic changes in static and dynamical properties of the quantum matter. The result is represented by the Gross-Pitaevskii equation for the BEC wave function with an extra quartic term [1[:
                                          
A striking property of QDs is stability of 3D and quasi-2D self-trapped droplets, which are kept together, as a variety of solitons, by the attraction between two BEC components, against the collapse (catastrophic self-compression), which is a fatal problem impeding the creation of stable 2D and 3D solitons in other systems. Following the prediction [1], QDs were quickly created in experiments [2,3]. It was predicted as well, although not yet demonstrated experimentally, that QDs with embedded vorticity have their stability regions too, on the contrary to the common belief that vortex solitons are unstable against spontaneous splitting. In optics, counterparts of QDs, supported by the cubic-quartic nonlinearity in Eq. (1), are realized in media with the cubic-quintic nonlinearity, which readily maintains stable 2D solitons in the experiment [4].
The objective of the talk is to present an overview of major experimental and theoretical findings made in these areas of atomic and optical physics in the course of the last five years, with emphasis on the prediction and creation of stable multidimensional QDs and solitons, especially those with embedded vorticity. Recent reviews of these results are provided in [5,6].
[1] D. S. Petrov, Quantum mechanical stabilization of a collapsing Bose-Bose mixture, Phys. Rev. Lett. 115, 155302 (2015).
[2] C. R. Cabrera et al., Quantum liquid droplets in a mixture of Bose–Einstein condensates, Science 359, 301 (2018).
[3] G. Semeghini et al, Self-bound quantum droplets in atomic mixtures Phys. Rev. Lett. 120, 235301 (2018).   
[4] L. Edilson et al., Robust two-dimensional spatial solitons in liquid carbon disulfide, Phys. Rev. Lett. 110, 013901 (2013). 
[5] Y. Kartashov, G. Astrakharchik, B. Malomed, L. Torner, Frontiers in multidimensional self-trapping of nonlinear fields and matter, Nature Reviews Physics 1, 185-197 (2019).
[6] Z. Luo, W. Pang, B. Liu, Y. Li, B. Malomed, A new form of liquid matter: quantum droplets, Front. Phys. 16