Localization of Cold Atoms in State-Dependent Optical Lattices via a Rabi Pulse

We propose a novel realization of Anderson localization in nonequilibrium states of ultracold atoms in an optical lattice. A Rabi pulse transfers part of the population to a different internal state with infinite effective mass. These frozen atoms create a quantum superposition of different disorder potentials, localizing the mobile atoms. For weakly interacting mobile atoms, Anderson localization is obtained. The localization length increases with increasing disorder and decreasing interaction strength, contrary to the expectation for equilibrium localization.

Figure 1

Sketch of atom localization in state-dependent optical lattices. The $a$ atoms, initially prepared in the ground state of the lattice, are converted to a quantum superposition $\cos (\alpha /2)|a⟩+\sin (\alpha /2)|b⟩$ by a Rabi pulse, where the $b$ atoms are frozen by the lattice. The state of the system can be viewed as $a$ atoms (red) moving in a quantum superposition of random potentials created by the frozen $b$ atoms (blue).

Figure 2

Time evolution of the density profile $n(x)=⟨n_{x/d}^a⟩$ for the noninteracting gas, $U_a=0$, after a pulse of duration $\alpha =\pi /2$ and with interspecies interaction $U_{ab}=7J_a$.

Figure 3

(a),(b): transferred energy per $a$ boson (a) for a noninteracting gas of $a$ bosons ($U_a=0$), and (b) for interacting $a$ bosons with $U_{ab}=7J_a$. (c),(d): corresponding localization length (in units of the lattice spacing $d$) of the evolved cloud.

Figure 4

Relative coherent fraction $R$ after time evolution (see text) for $U_{ab}=7J_a$.