Ground-State Phase Diagram of a Spin-Orbital-Angular-Momentum Coupled Bose-Einstein Condensate

Abstract

Orbital angular momentum (OAM) of light represents a fundamental optical freedom that can be exploited to manipulate quantum state of atoms. In particular, it can be used to realize spinorbital-angular-momentum (SOAM) coupling in cold atoms by inducing an atomic Raman transition using two laser beams with differing OAM. Rich quantum phases are predicted to exist in manybody systems with SOAM coupling. Their observations in laboratory, however, are often hampered by the limited control of the system parameters. In this work we report, for the first time, the experimental observation of the ground-state quantum phase diagram of the SOAM coupled Bose-Einstein condensate (BEC). The discontinuous variation of the spin polarization as well as the vorticity of the atomic wave function across the phase boundaries provides clear evidence of firstorder phase transitions. Our results open up a new way to the study of phase transitions and exotic quantum phases in quantum gases. arXiv:1806.06263v2 [cond-mat.quant-gas]

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.…”

“…The method works if the frequency of the magnetic level splitting ω 0 is much larger than the driving frequency ω. In the experiment [99] with 87 Rb atoms, the magnetic splitting frequency ω 0 = 2π × 4.81MHz far exceeds the recoil frequency ω rec which equals to 2π × 3.77kHz for the 780nm 5 2 S 1/2 → 5 2 P 3/2 optical transition. Note that the bias magnetic field induces also the quadratic Zeeman shift (QZS) with a frequency equal approximately to 6ω rec in the experiment [99].…”

Novel quantum states with laser cooling and their detection

“…Three phases are denoted by the quasi-orbital-angular momentum, l z =1, 0, -1, respectively. The solid curves denote the calculated phase boundaries including the many-body interaction [29].…”

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]. However, in current studies, only the Abelian type spin-orbital-angular-momentum (SOAM) coupled interaction L z F z is considered, where L z and F z represent the atomic OAM and internal spin operators in the z-direction respectively.…”