In-situ Observation of Incompressible Mott-Insulating Domains of Ultracold Atomic Gases

TL;DR

This study uses high-resolution imaging to directly observe the spatial structure and local properties of a two-dimensional Mott insulator formed by ultracold atoms, revealing detailed phase boundaries and fluctuation suppression.

Contribution

It provides the first direct, spatially resolved measurements of density, compressibility, and fluctuations in a 2D ultracold atomic Mott insulator, confirming theoretical predictions.

Findings

Strong suppression of compressibility in the Mott phase

Fluctuation suppression in the insulator

Consistency with fluctuation-dissipation theorem

Abstract

We present a direct measurement of the density profile of a two-dimensional Mott Insulator formed by ultracold atoms in an optical lattice. High resolution absorption imaging is used to probe the "wedding-cake" structure of a trapped gas as it crosses the boundary from a unit-filled Mott insulating phase to the superfluid phase at finite temperature. Detailed analysis of images yields measurements of temperature and local compressibility; for the latter we observe a strong suppression deep in the Mott-insulating phase, which is recovered for the superfluid and normal phases. Furthermore, we measure spatially resolved fluctuations in the local density, showing a suppression of fluctuations in the insulator. Results are consistent with the fluctuation-dissipation theorem for insulator, superfluid and normal gas.