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arXiv:1505.08152 · Physical Review Letters

Probing the Excitations of a Lieb-Liniger Gas from Weak to Strong Coupling

Florian Meinert, Miłosz Panfil, Manfred J. Mark, Katharina Lauber, Jean-Sébastien Caux, Hanns‐Christoph Nägerl

Published Aug 20, 2015• 166 citations
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Abstract

We probe the excitation spectrum of an ultracold one-dimensional Bose gas of cesium atoms with a repulsive contact interaction that we tune from the weakly to the strongly interacting regime via a magnetic Feshbach resonance. The dynamical structure factor, experimentally obtained using Bragg spectroscopy, is compared to integrability-based calculations valid at arbitrary interactions and finite temperatures. Our results unequivocally underlie the fact that holelike excitations, which have no counterpart in higher dimensions, actively shape the dynamical response of the gas.

DOI
10.1103/physrevlett.115.085301

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While the one-dimensional (1D) Bose gas appears to exhibit superfluid response under certain conditions, it fails the Landau criterion according to the elementary excitation spectrum calculated by Lieb. The apparent riddle is solved by calculating the dynamic structure factor of the Lieb-Liniger 1D Bose gas. In a dual representation, strongly interacting bosons are mapped into weakly interacting fermions, which are treated in the Hartree-Fock and generalized random-phase approximations. The dynamic structure factor is calculated analytically in this approximation, which is valid to first order in $1∕\ensuremath{\gamma}$, where $\ensuremath{\gamma}$ is the dimensionless interaction strength of the model. The results clearly indicate a suppression of superfluidity-breaking umklapp excitations near the Tonks-gas limit, which should be observable by Bragg scattering in current experiments.
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We address the problem of calculating finite-temperature response functions of an experimentally relevant low-dimensional, strongly correlated system: the integrable one-dimensional Bose gas with a repulsive $\ensuremath{\delta}$-function interaction (the Lieb-Liniger model). Focusing on the dynamical density-density function, we present a Bethe ansatz-based method allowing for its accurate evaluation in finite but large systems, over broad ranges of momenta, frequencies, temperatures, and interaction parameters which are difficult to access using other methods. This allows us to quantify the reshaping of the zero-temperature critical behavior by thermal fluctuations, in experimentally accessible regimes.