Realization of a fractional period adiabatic superlattice

We propose and realize a deeply sub-wavelength optical lattice for ultracold neutral atoms using $N$ resonantly Raman-coupled internal degrees of freedom. Although counter-propagating lasers with wavelength $\lambda$ provided two-photon Raman coupling, the resultant lattice-period was $\lambda \mathrm{/}2N$, an $N$-fold reduction as compared to the conventional $\lambda \mathrm{/}2$ lattice period. We experimentally demonstrated this lattice built from the three $F=1$ Zeeman states of a ${}^{87}\mathrm{R}\mathrm{b}$ Bose-Einstein condensate, and generated a lattice with a $\lambda \mathrm{/}6=132\mathrm{n}\mathrm{m}$ period from $\lambda =790\mathrm{n}\mathrm{m}$ lasers. Lastly, we show that adding an additional RF coupling field converts this lattice into a superlattice with $N$ wells uniformly spaced within the original $\lambda \mathrm{/}2$ unit cell.