Laser-Induced Kondo Effect in Ultracold Alkaline-Earth Fermions

We demonstrate that laser excitations can coherently induce a novel Kondo effect in ultracold atoms in optical lattices. Using a model of alkaline-earth fermions with two orbitals, it is shown that the optically coupled two internal states are dynamically entangled to form the Kondo-singlet state, overcoming the heating effect due to the irradiation. Furthermore, a lack of $\mathrm{SU}(N)$ symmetry in the optical coupling provides a peculiar feature in the Kondo effect, which results in spin-selective renormalization of effective masses. We also discuss the effects of interorbital exchange interactions, and reveal that they induce novel crossover or reentrant behavior of the Kondo effect owing to control of the coupling anisotropy. The laser-induced Kondo effect is highly controllable by tuning the laser strength and the frequency, and thus offers a versatile platform to study the Kondo physics using ultracold atoms.

Figure 1

(a) Schematic picture of the setup. Fermionic atoms in the ${}^1{S}_0$ state can move between sites of the optical lattice, while those in the ${}^3{P}_0$ state cannot. (b) The energy level shift after the gauge transformation. (c) Renormalized hybridization calculated with parameters $D=1$, ${ϵ}_f=-0.5$, $T_0=0$, ${\mu }_0=-0.1$, and $N=2,6,10$. (d) Effective temperatures calculated with the same parameters. The broken lines show the Kondo temperature $T_K$.

Figure 2

(a) The renormalized quasiparticle band induced by the laser-induced Kondo effect for $N=6$. (b) Population imbalance induced by the Kondo effect. The $N=10$ case is shown, with parameters $D=1$, ${ϵ}_f=-0.8$, $T_0=0$, ${\mu }_0=-0.5$. $N_{\sigma }=n_{\sigma }+n_{-\sigma }$ is the particle number of each spin component.

Figure 3

The renormalization group flow for the case of the Kondo impurity for $N=2$. The blue (red) line shows a trajectory of the coupling constants when we apply the external laser in the case of $V_{\mathrm{ex}}>0$ ($V_{\mathrm{ex}}<0$).