Diffraction of strongly interacting molecular Bose-Einstein condensate from standing wave light pulses

Abstract

We study the effects of strong inter-particle interaction on diffraction of a Bose-Einstein condensate of 6 Li 2 molecules from a periodic potential created by pulses of a far detuned optical standing wave. For short pulses we observe the standard Kapitza-Dirac diffraction, with the contrast of the diffraction pattern strongly reduced for very large interactions due to interaction dependent loss processes. For longer pulses diffraction shows the characteristic for matter waves impinging on an array of tubes and coherent channeling transport. We observe a slowing down of the time evolution governing the population of the momentum modes caused by the strong atom interaction. A simple physical explanation of that delay is the phase shift caused by the self interaction of the forming mater wave patters inside the standing light wave. The phenomenon can be reproduced with onedimensional mean-field simulation. In addition two contributions to interactiondependent degradation of the coherent diffraction patterns were identified: (i) in-trap loss of molecules during the lattice pulse, which involves dissociation of Feshbach molecules into free atoms, as confirmed by radio-frequency spectroscopy and (ii) collisions between different momentum modes during separation. This was confirmed by interferometrically recombining the diffracted momenta into the zero-momentum peak, which consequently removed the scattering background.