Optically Induced Spin-Hall Effect in Atoms

Abstract

We propose an optical means to realize a spin hall effect (SHE) in neutral atomic system by coupling the internal spin states of atoms to radiation. The interaction between the external optical fields and the atoms creates effective magnetic fields that act in opposite directions on "electrically" neutral atoms with opposite spin polarizations. This effect leads to a Landau level structure for each spin orientation in direct analogy with the familiar SHE in semiconductors. The conservation and topological properties of the spin current, and the creation of a pure spin current are discussed. PACS numbers: 72.25.Fe, 32.80.Qk, 72.25.Hg, 03.75.Lm Information devices based on spin states of particles require a lot less power consumption than equivalent charge based devices [1]. To implement practical spin-based logical operations, a basic underlying theory, i.e. spin hall effect (SHE) has been widely studied for the creation of spin currents in semiconductors [2,3,4,5]. Nearly all current publications on SHE involve some form of spinorbit coupling, including the interaction between charged particles in semiconductors and external electric field. The physics of SHE in semiconductors is: in the presence of spin-orbit coupling, the applied electric field leads to a transverse motion (perpendicular to the electric field), with spin-up and spin-down carriers moving oppositely to each other, creating a transverse spin current. However, spin current can also be generated by interacting optical fields with charged particles in semiconductors [6,7], even in absence of spin-orbit coupling [8].In this letter, we show how SHE can be induced by optical fields in neutral atomic system. Quantum states of atoms can be manipulated by coupling their internal degrees of freedom (atomic spin states) to radiation, making it possible to control atomic spin propagation through optical methods. We consider here an ensemble of cold Fermi atoms interacting with two external light fields (Fig. 1). The ground (|g ± , ± 1 2 ) and excited (|e ± , ± 1 2 ) states are hyperfine angular momentum states (atomic spins) with their total angular momenta F g = F e = 1/2. The transitions from |g − , − 1 2 to |e + , 1 2 and from |g + , 1 2 to |e − , − 1 2 are coupled respectively by a σ + light with the Rabi-frequency Ω 2 = Ω 20 exp(i(k 2 · r + l 2 ϑ)) and by a σ − light with the Rabi-frequency Ω 1 = Ω 10 exp(i(k 1 · r + l 1 ϑ)), where k 1,2 = k 1,2êz are the wave-vectors and ϑ = tan −1 (y/x). l 1 and l 2 indicate that σ + and σ − photons are assumed to have the orbital angular momentum l 1 and * Electronic address: phylx@nus.edu.sg † Electronic address: phyohch@nus.edu.sg FIG. 1: Fermi atoms with four-level internal hyperfine spin states interacting with two light fields. This can be experimentally realized with alkali atoms, such as 6 Li atomsl 2 along the +z direction, respectively [10]. For simplicity, we replace the notations |α ± , ± 1 2 by |α ± (α = e, g). The r-representation atomic wave function is denoted by Φ α (r, t). It is helpful to introdu...

Spin-orbit-coupling-induced half-skyrmion excitations in rotating and rapidly quenched spin-1 Bose-Einstein condensates

“…Recently, spin-orbit coupled Bose-Einstein condensate (BEC) has been realized experimentally in NIST [10]. Unlike the previous experiment, their work has factually explored the bosons system in the nonAbelian gauge field [11][12][13][14][15][16][17][18]. This opens up a new avenue in cold atom physics and attracts much attention.…”

Influences of a topological defect on the spin Hall effect

“…This effect, which occurs as a result of the spin-orbit coupling (SOC) between electrons and impurities, is called extrinsic [4]. Conversely, there are intrinsic forms of the SHE [5][6][7][8], which is caused by spin-orbit coupling in the band structure of the semiconductor and survives in the limit of zero disorder, and has became an active field of research in recent years [9][10][11][12][13]. Generally, the spin current is non conserved because of the exchange of angular momentum between the electrons and acting fields through the spin-orbital coupling.…”

Vortex structures of rotating spin-orbit-coupled Bose-Einstein condensates

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