Exploring multiband excitations of interacting Bose gases in a one-dimensional optical lattice by coherent scattering

We use a coherent Bragg diffraction method to impart an external momentum to ultracold bosonic atoms trapped in a one-dimensional optical lattice. This method is based on the application of a single light pulse, with conditions where scattering of photons can be resonantly amplified by atomic density grating. An oscillatory behavior of the momentum distribution resulting from the time evolution in the lattice potential is then observed. By measuring the oscillating frequencies, we extract multiband energy structures of single-particle excitations with zero pseudomomentum transfer for a wide range of lattice depths. The excitation energy structures reveal the interaction effect through the whole range of lattice depths.