Lattice Solitons in Quasicondensates

We analyze finite temperature effects in the generation of bright solitons in condensates in optical lattices. We show that even in the presence of strong phase fluctuations solitonic structures with a well defined phase profile can be created. We propose a novel family of variational functions which describe well the properties of these solitons and account for the nonlinear effects in the band structure. We discuss also the mobility and collisions of these localized wave packets.

Figure 1

Density and phase (inset) profile (a) of magnetically trapped (${\omega }_x=14\times 2\pi \mathrm{Hz}$) ${}^{87}\mathrm{R}\mathrm{b}$ ground state condensate with $N=500$ at $T=0.8T_c$, (b) after the adiabatic growing of the optical lattice ($V_0=1E_r$ and $\lambda =795\mathrm{nm}$), (c) of lattice soliton 100 ms after the imprinting of a phase difference of $\pi$ between consecutive wells and after the magnetic trap is switched off, and (d) of lattice soliton generated under the same conditions of (c) but at $T=0$.

Figure 2

Collisions between two identical lattice solitons ($N=200$) at an initial distance of $2x_0=246d$ and with an initial phase difference of (a) $\Delta \varphi =0\mathrm{rad}$, (b) $\Delta \varphi =\pi /2\mathrm{rad}$, (c) $\Delta \varphi =0.3\mathrm{rad}$, and (d) $\Delta \varphi =0.9\mathrm{rad}$. The initial transfer of momentum is $0.1k\hslash$ in all the cases.