[show abstract][hide abstract] ABSTRACT: We investigate experimentally and theoretically the dynamical properties of a
Mott insulator in decoupled one-dimensional chains. Using a theoretical
analysis of the Bragg excitation scheme we show that the spectrum of inter-band
transitions holds information on the single-particle Green's function of the
insulator. In particular the existence of particle-hole coherence due to
quantum fluctuations in the Mott state is clearly seen in the Bragg spectra and
quantified. Finally we propose a scheme to directly measure the full, momentum
resolved spectral function as obtained in angle-resolved photoemission
spectroscopy of solids.
[show abstract][hide abstract] ABSTRACT: Using inelastic scattering of light (Bragg spectroscopy), we study the low-energy excitations of strongly correlated phases
of ultracold bosons on the cross-over from correlated 1D superfluids to Mott insulators. As it is commonly performed in solid-state
physics, the use of such a probe allows us to extract important information about the atomic many-body state. In particular
we show that we can extract information about the dynamical structure factor S(q,ω) and about the one-particle spectral function A(q,ω) from the Bragg spectra. This technique could be extended to study more exotic correlated phases of ultracold atoms.
Journal of Low Temperature Physics 04/2012; 158(1):5-15. · 1.18 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have used inelastic light scattering to study correlated phases of an array of one-dimensional interacting Bose gases. In the linear response regime, the observed spectra are proportional to the dynamic structure factor. In particular we have investigated the superfluid to Mott insulator crossover loading the one-dimensional gases in an optical lattice and monitoring the appearance of an energy gap due to finite particle-hole excitation energy. We attribute the low frequency side of the spectra to the presence of some superfluid and normal phase fraction between the Mott insulator regions with different fillings produced in the inhomogeneous systems. In the Mott phase we also investigated excitations to higher excited bands of the optical lattice, the spectra obtained in this case being connected to the single particle spectral function. In one-dimensional systems the effect of thermal fluctuations and interactions is enhanced by the reduced dimensionality showing up in the dynamic structure factor. We measured the dynamic structure factor of an array of one-dimensional bosonic gases pointing out the effect of temperature-induced phase fluctuations in reducing the coherence length of the system.
Journal of Physics Conference Series 01/2011; 264(1):012018.
[show abstract][hide abstract] ABSTRACT: We investigate the coherence properties of an array of one-dimensional Bose gases with short-scale phase fluctuations. The momentum distribution is measured using Bragg spectroscopy, and an effective coherence length of the whole ensemble is defined. In addition, we propose and demonstrate that time-of-flight absorption imaging can be used as a simple probe to directly measure the coherence length of one-dimensional gases in the regime where phase fluctuations are strong. This method is suitable for future studies such as investigating the effect of disorder on the phase coherence.
Physical Review A 01/2011; 83:031604. · 3.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: We investigate the coherence properties of an array of one-dimensional Bose gases with short-scale phase fluctuations. The momentum distribution is measured using Bragg spectroscopy and an effective coherence length of the whole ensemble is defined. In addition, we propose and demonstrate that time-of-flight absorption imaging can be used as a simple probe to directly measure the coherence-length of 1D gases in the regime where phase-fluctuations are strong. This method is suitable for future studies such as investigating the effect of disorder on the phase coherence. Comment: 4 pages, 4 figures
[show abstract][hide abstract] ABSTRACT: Light scattering is used to extract information on the state of ultracold bosonic gases trapped in optical lattices. Different regimes of interactions are explored, ranging from weakly interacting 3D Bose-Einstein condensates to strongly interacting 1D gases in the crossover from superfluid to Mott-insulating states.
[show abstract][hide abstract] ABSTRACT: We report the Bragg spectroscopy of interacting one-dimensional Bose gases loaded in an optical lattice across the superfluid to the Mott-insulator phase transition. Elementary excitations are created with a nonzero momentum and the response of the correlated 1D gases is in the linear regime. The complexity of the strongly correlated quantum phases is directly displayed in the spectra which exhibit novel features. This work paves the way for a precise characterization of the state of correlated gases in optical lattices.
[show abstract][hide abstract] ABSTRACT: We report on the experimental investigation of the response of a three-dimensional Bose-Einstein condensate (BEC) in the presence of a one-dimensional (1D) optical lattice. By means of Bragg spectroscopy we probe the band structure of the excitation spectrum in the presence of the periodic potential. We selectively induce elementary excitations of the BEC choosing the transferred momentum and we observe different resonances in the energy transfer, corresponding to the transitions to different bands. The frequency, the width and the strength of these resonances are investigated as a function of the amplitude of the 1D optical lattice. Comment: 5 pages, 4 figures
Physical Review A 01/2009; 79:043623. · 3.04 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this work, we use inelastic scattering of light to study the response of inhomogeneous Mott-insulator gases to external excitations. The experimental setup and procedure to probe the atomic Mott states are presented in detail. We discuss the link between the energy absorbed by the gases and accessible experimental parameters as well as the linearity of the response to the scattering of light. We investigate the excitations of the system in multiple energy bands and a band-mapping technique allows us to identify band and momentum of the excited atoms. In addition the momentum distribution in the Mott states which is spread over the entire first Brillouin zone enables us to reconstruct the dispersion relation in the high energy bands using a single Bragg excitation with a fixed momentum transfer. Comment: 19 pages, 7 figures
New Journal of Physics 01/2009; 11:103030. · 4.06 Impact Factor