The Quantum Gas Magnifier as a Coherence Microscope

Imaging is crucial for gaining insight into physical systems. In the case of ultracold atoms in optical lattices, the novel technique of quantum gas magnification opens the way to explore 3D systems with large occupation numbers with sub-lattice site resolution.

We report on the realization of an all-optical quantum gas magnifier for ultracold Lithium-7 atoms. The all-optical approach allows us to address the broad Feshbach resonance of Lithium to control the interaction strength. With this technique, we directly image the Talbot carpet that forms when releasing the atoms from an optical lattice. After certain ballistic expansion times, the wave packets originating from each lattice site overlap and constructively interfere with each other, such that an image of the original density distribution is obtained. We map out the spatial coherence by analyzing the contrast of consecutive Talbot copies. The technique should also allow to reconstruct the fluctuating phase profile of individual samples imaged at a single Talbot copy. This will realize a coherence microscope with spatially resolved access to phase information allowing to study domain walls, thermally activated vortex pairs, or to locally evaluate coherence in inhomogeneous quantum many-body systems.