A new form of liquid matter: Quantum droplets
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Front. Phys. 16(3), 32201 (2021)
Review article A new form of liquid matter: Quantum droplets Zhi-Huan Luo1 , Wei Pang2 , Bin Liu3 , Yong-Yao Li3,† , Boris A. Malomed4,5 1
Department of Applied Physics, South China Agricultural University, Guangzhou 510642, China Department of Experiment Teaching, Guangdong University of Technology, Guangzhou 510006, China 3 School of Physics and Optoelectronic Engineering, Foshan University, Foshan 528000, China Department of Physical Electronics, School of Electrical Engineering, Faculty of Engineering, and Center for Light-Matter Interaction, Tel Aviv University, Tel Aviv 69978, Israel 5 Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile Corresponding author. E-mail: † [email protected] Received September 2, 2020; accepted October 19, 2020 2
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This brief review summarizes recent theoretical and experimental results which predict and establish the existence of quantum droplets (QDs), i.e., robust two- and three-dimensional (2D and 3D) selftrapped states in Bose–Einstein condensates (BECs), which are stabilized by effective self-repulsion induced by quantum fluctuations around the mean-field (MF) states [alias the Lee–Huang–Yang (LHY) effect]. The basic models are presented, taking special care of the dimension crossover, 2D → 3D. Recently reported experimental results, which exhibit stable 3D and quasi-2D QDs in binary BECs, with the inter-component attraction slightly exceeding the MF self-repulsion in each component, and in single-component condensates of atoms carrying permanent magnetic moments, are presented in some detail. The summary of theoretical results is focused, chiefly, on 3D and quasi-2D QDs with embedded vorticity, as the possibility to stabilize such states is a remarkable prediction. Stable vortex states are presented both for QDs in free space, and for singular but physically relevant 2D modes pulled to the center by the inverse-square potential, with the quantum collapse suppressed by the LHY effect. Keywords quantum droplet, Bose–Einstein condensate, Lee–Huang–Yang correction, votex state
Contents
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Introduction Theoretical models of quantum droplets 2.1 Models of QDs in three, two, and one dimensions 2.2 Dimensional crossover for quantum droplets 3 Experimental observations of two-component quantum droplets (QDs) 3.1 Oblate (quasi-two-dimensional droplets) 3.2 Three-dimensional (isotropic) droplets 3.3 Collisions between quantum droplets 3.4 Droplets in a heteronuclear bosonic mixture 4 Single-component QDs in dipolar condensates 4.1 Quantum droplets in the condensate of dysprosium 4.2 Quantum droplets in the condensate of erbium
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The list of acronyms 10
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for a View & Perspective. This article can also be found at http://journal.hep.com.cn/fop/EN/10.1007/ s11467-020-1020-2 and arXiv: 2009.01061.
Theoretical results: Stable quantum droplets with embedded vorticity 5.1 Three-dimensional vortex rings 5.2 Two-dimensional vortex rings and necklaces 5.2.1 Basic results 5.2.2 Semidis
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