Increased Dimensionality of Raman Cooling in a Slightly Nonorthogonal Optical Lattice

TL;DR

This paper demonstrates that slight nonorthogonality in a 2D optical lattice allows for rotated eigenmodes, enabling efficient two-dimensional Raman ground-state cooling of a single atom, expanding cooling capabilities in optical trapping.

Contribution

It introduces a method to rotate eigenmodes via trap frequency tuning in a nonorthogonal lattice, enabling 2D Raman cooling where it was previously impossible.

Findings

Achieved 2D Raman ground-state cooling in a nonorthogonal lattice.

Eigenmodes can be rotated by tuning trap frequencies.

The scheme is adaptable to various experimental setups.

Abstract

We experimentally study the effect of a slight nonorthogonality in a two-dimensional optical lattice onto resolved-sideband Raman cooling. We find that when the trap frequencies of the two lattice directions are equal, the trap frequencies of the combined potential exhibit an avoided crossing and the corresponding eigenmodes are rotated by 45 degrees relative to the lattice beams. Hence, tuning the trap frequencies makes it possible to rotate the eigenmodes such that both eigenmodes have a large projection onto any desired direction in the lattice plane, in particular, onto the direction along which Raman cooling works. Using this, we achieve two-dimensional Raman ground-state cooling in a geometry where this would be impossible, if the eigenmodes were not rotated. Our experiment is performed with a single atom inside an optical resonator but this is inessential and the scheme is expected to work equally well in other situations.