Quantum phases of Bose-Einstein condensates with synthetic spin–orbital-angular-momentum coupling

Abstract

The experimental realization of emergent spin-orbit coupling through laser-induced Raman transitions in ultracold atoms paves a way for exploring novel superfluid physics and simulating exotic many-body phenomena. A recent proposal with the use of Laguerre-Gaussian lasers enables another fundamental type of coupling between spin and orbital angular momentum (SOAM) in ultracold atoms. We hereby study quantum phases of a realistic Bose-Einstein condensate (BEC) with this synthetic SOAM coupling in a disk-shaped geometry, respecting radial inhomogeneity of the Raman coupling. We find that the experimental system naturally resides in a strongly interacting regime in which the phase diagram significantly deviates from the single-particle picture. The interplay between SOAM coupling and interaction leads to rich structures in spin-resolved position and momentum distributions, including a stripe phase and various types of immiscible states. Our results would provide a guide for an experimental investigation of SOAM-coupled BECs.

Spin–Orbital-Angular-Momentum Coupled Bose-Einstein Condensates

“…The nature of transition between different superfluid phases may be characterized by calculating the derivative of the mean-field energy with respect to the Rabi frequency [16,17], ∂ǫ/∂Ω, as shown in Fig. 2(c) with vertical dashed and dotted lines for the second-and first-order transitions, respectively.…”

“…In addition to the Raman SOC, a new type of SOC, the so-called spin-orbital-angular-momentum coupling (SOAMC), has been recently proposed in pioneering theoretical works [15][16][17][18][19]: by utilizing two co-propagating Laguerre-Gaussian (LG) laser beams to induce an offdiagonal Stark shift, the atomic pseudospin can be coupled to its angular momentum. The resulting SOAMC is of a two-dimensional (2D) nature with an axial symmetry, which gives rise to intriguing quantum phases, such as the vortex-antivortex pair phase (see the phase I in Fig.…”

Non-Abelian geometric potentials and spin-orbit coupling for periodically driven systems

“…On the other hand, the term L xFx + L yFy = L +F− + L −F+ represents transitions between different spin and OAM projection states described by the raising / lowering operators L ± = L x ± iL y andF ± =F x ± iF y . Therefore the present SOC has some similarities to the coupling between the spin and OAM induced by Raman laser beams carrying optical vortices [76][77][78][79][80][81][82][83][84][85][86][87]. Yet, unlike the Raman case now the coupling between the spin and OAM is described by all three OAM projections L x , L y and L z as long as α ⊥ = 0 and α z = 0, so the coupling is truly three dimensional.…”

Topological spinor vortex matter on spherical surface induced by non-Abelian spin-orbital-angular-momentum coupling

“…Although most current investigations focus on SLM coupled quantum gases, as another type of spin-orbit coupled physics, coupling between atomic spin with its orbital angular momentum (OAM) degree of freedom has also received considerable attention recently [36][37][38][39][40][41][42][43][44][45]. Experimentally, this has been achieved by coupling different atomic spin states with laser beams carrying different OAMs [42][43][44].…”