arXiv subjects

Daniel Greif

Publications and source records attributed to Daniel Greif.

23 records · Page 2Linked to original sources

arXiv2011

Probing nearest-neighbor correlations of ultracold fermions in an optical lattice

We demonstrate a probe for nearest-neighbor correlations of fermionic quantum gases in optical lattices. It gives access to spin and density configurations of adjacent sites and relies on creating additional doubly occupied sites by perturbative lattice modulation. The measured correlations for different lattice temperatures are in good agreement with an ab initio calculation without any fitting parameters. This probe opens new prospects for studying the approach to magnetically ordered phases.

cond-mat.quant-gas↗

arXiv2010

Quantitative Determination of Temperature in the Approach to Magnetic Order of Ultracold Fermions in an Optical Lattice

We perform a quantitative simulation of the repulsive Fermi-Hubbard model using an ultracold gas trapped in an optical lattice. The entropy of the system is determined by comparing accurate measurements of the equilibrium double occupancy with theoretical calculations over a wide range of parameters. We demonstrate the applicability of both high-temperature series and dynamical mean-field theory to obtain quantitative agreement with the experimental data. The reliability of the entropy determination is confirmed by a comprehensive analysis of all systematic errors. In the center of the Mott insulating cloud we obtain an entropy per atom as low as 0.77kB which is about twice as large as the entropy at the Neel transition. The corresponding temperature depends on the atom number and for small fillings reaches values on the order of the tunneling energy.

cond-mat.quant-gas↗

arXiv2010

Observation of Elastic Doublon Decay in the Fermi-Hubbard Model

We investigate the decay of highly excited states of ultracold fermions in a three-dimensional optical lattice. Starting from a repulsive Fermi-Hubbard system near half filling, we generate additional doubly occupied sites (doublons) by lattice modulation. The subsequent relaxation back to thermal equilibrium is monitored over time. The measured doublon lifetime covers two orders of magnitude. In units of the tunneling time h/J it is found to depend exponentially on the ratio of on-site interaction energy U to kinetic energy J. We argue that the dominant mechanism for the relaxation is a high order scattering process involving several single fermions as scattering partners. A many-body calculation is carried out using diagrammatic methods, yielding good agreement with the data.

cond-mat.quant-gas↗

arXiv2010

Lifetime of double occupancies in the Fermi-Hubbard model

We investigate the decay of artificially created double occupancies in a repulsive Fermi-Hubbard system in the strongly interacting limit using diagrammatic many-body theory and experiments with ultracold fermions on optical lattices. The lifetime of the doublons is found to scale exponentially with the ratio of the on-site repulsion to the bandwidth. We show that the dominant decay process in presence of background holes is the excitation of a large number of particle hole pairs to absorb the energy of the doublon. We also show that the strongly interacting nature of the background state is crucial in obtaining the correct estimate of the doublon lifetime in these systems. The theoretical estimates and the experimental data are in fair quantitative agreement.

cond-mat.quant-gas↗

arXiv2009

Versatile transporter apparatus for experiments with optically trapped Bose-Einstein condensates

We describe a versatile and simple scheme for producing magnetically and optically-trapped Rb-87 Bose-Einstein condensates, based on a moving-coil transporter apparatus. The apparatus features a TOP trap that incorporates the movable quadrupole coils used for magneto-optical trapping and long-distance magnetic transport of atomic clouds. As a stand-alone device, this trap allows for the stable production of condensates containing up to one million atoms. In combination with an optical dipole trap, the TOP trap acts as a funnel for efficient loading, after which the quadrupole coils can be retracted, thereby maximizing optical access. The robustness of this scheme is illustrated by realizing the superfluid-to-Mott insulator transition in a three-dimensional optical lattice.

cond-mat.quant-gas↗