Bragg spectroscopy of strongly interacting bosons in optical lattices

Inelastic light scattering is an experimental technique largely used in condensed-matter physics, providing important information about the dynamics of the excitations of a system. We are interested in many-body quantum systems of ultracold atoms with strong correlations between the particles. They are among the most intriguing physical systems, since no simple picture captures their behaviour. In this work, we study one-dimensional (1d) ultracold gases in optical lattices: they allows us to create strongly correlated quantum phases in a highly controllable way. We induce the crossover between a strongly correlated superfluid and an inhomogeneous Mott insulator phase by the presence of an optical lattice in the direction of the 1d gases. Using light scattering (Bragg spectroscopy [1]) we probe the excitations of the system in a linear response regime unaccessible to previous works. Low-energy excitations of the system exhibits signficant modification when the system is driven into the insulating phase by tuning the amplitude of the lattice [2]. The presence of the optical lattice also induces an energy band structure in the system: combining Bragg spectroscopy with a band-mapping technique, we probe the dispersion relation in such higher energy bands. [1] M. Kozuma et al., Phys. Rev. Lett. 82,871 (1999); J. Stenger et al., Phys. Rev. Lett. 82, 4569 (1999); R. Ozeri et al. Rev. Mod. Phys. 77, 187 (2005) [2] D. Clément, N. Fabbri, L. Fallani, C. Fort and M. Inguscio, Phys. Rev. Lett. 102, 155301 (2009)