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

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. PACS numbers: 73.43.Nq,03.75.Kk,05.30.Jp,03.75.Lm The observation of the Superfluid (SF) to Mottinsulator (MI) phase transition of ultracold atoms in optical lattices [1] marked an experimental breakthrough in the study of many-body physics in an atomic system. This development provided the first tangible exampl

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