Properties of spin–orbit-coupled Bose–Einstein condensates

Abstract

The experimental and theoretical research of spin-orbit-coupled ultracold atomic gases has advanced and expanded rapidly in recent years. Here, we review some of the progress that either was pioneered by our own work, has helped to lay the foundation, or has developed new and relevant techniques. After examining the experimental accessibility of all relevant spin-orbit coupling parameters, we discuss the fundamental properties and general applications of spin-orbit-coupled Bose-Einstein condensates (BECs) over a wide range of physical situations. For the harmonically trapped case, we show that the ground state phase transition is a Dicke-type process and that spin-orbit-coupled BECs provide a unique platform to simulate and study the Dicke model and Dicke phase transitions. For a homogeneous BEC, we discuss the collective excitations, which have been observed experimentally using Bragg spectroscopy. They feature a roton-like minimum, the softening of which provides a potential mechanism to understand the ground state phase transition. On the other hand, if the collective dynamics are excited by a sudden quenching of the spin-orbit coupling parameters, we show that the resulting collective dynamics can be related to the famous Zitterbewegung in the relativistic realm. Finally, we discuss the case of a BEC loaded into a periodic optical potential. Here, the spin-orbit coupling generates isolated flat bands within the lowest Bloch bands whereas the nonlinearity of the system leads to dynamical instabilities of these Bloch waves. The experimental verification of this instability illustrates the lack of Galilean invariance in the system.

Two-dimensional solitons and quantum droplets supported by competing self- and cross-interactions in spin-orbit-coupled condensates

“…It was predicted too that 2D and 3D solitons can be stabilized in spinor (two-component) BECs with the help of the spin-orbit coupling (SOC) of the Rashba type [13][14][15][16][17][18][19][20][21]. There are two types of multidimensional solitons in this system, viz ., semi-vortices (SVs) and mixed modes (MMs).…”

Optical-lattice-assisted magnetic phase transition in a spin-orbit-coupled Bose-Einstein condensate

“…Spin-orbit-coupled Bose-Einstein condensates (BECs) are characterized by a rich variety of quantum phases, which have already been the subject of theoretical and experimental investigations (see the recent reviews [1][2][3][4][5][6][7] and references therein). In particular, in the case of a BEC of pseudospin 1/2 with equal Rashba [8] and Dresselhaus [9] spin-orbit couplings, by tuning the value of the Raman coupling between the two pseudospin states one can explore different phase transitions.…”

Spin–orbit coupling in the presence of strong atomic correlations

“…The effect SOC has in BECs can be understood within the mean-field approximation of a two-component gas by calculating the dispersion relation and the related phase diagram [8][9][10][11]. In this regime three distinct phases can exist when the two components are in the miscible regime and when all interactions are repulsive.…”