# Realization of a fractional period adiabatic superlattice

## TL;DR

This paper demonstrates a novel optical lattice for ultracold atoms with a fractional period significantly smaller than the wavelength, achieved through resonant Raman coupling, and introduces a superlattice structure.

## Contribution

The work introduces a method to create sub-wavelength optical lattices using Raman coupling, achieving periods as small as one-sixth of the laser wavelength, and demonstrates a superlattice configuration.

## Key findings

- Achieved a lattice period of λ/6 (132 nm) from 790 nm lasers.
- Demonstrated the creation of a superlattice with multiple wells within the original lattice period.
- Experimental realization using a Bose-Einstein condensate of rubidium-87 atoms.

## Abstract

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 $\lambda/2N$, an $N$-fold reduction as compared to the conventional $\lambda/2$ lattice period. We experimentally demonstrated this lattice built from the three $F=1$ Zeeman states of a $^{87}{\rm Rb}$ Bose-Einstein condensate, and generated a lattice with a $\lambda/6= 132\ {\rm nm}$ period from $\lambda=790 \ {\rm nm}$ 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 $\lambda/2$ unit cell.