Eugene Demler

TL;DR: In this paper, an antiferromagnetic long-range order (LRO) was observed in a repulsively interacting Fermi gas on a 2D square lattice of approximately 80 sites.

TL;DR: In this article, the authors study the dynamics of a rapidly and coherently split one-dimensional Bose gas and show that the system dephases to a prethermalized state rather than undergoing thermalization toward a final thermal equilibrium state.

Abstract: Recent experimental achievements in controlling ultracold gases in optical lattices open a new perspective on quantum many-body physics. In these experimental setups it is possible to study coherent time evolution of isolated quantum systems. These dynamics reveal new physics beyond the low-energy properties usually relevant in solid-state many-body systems. In this paper we study the time evolution of antiferromagnetic order in the Heisenberg chain after a sudden change of the anisotropy parameter, using various numerical and analytical methods. As a generic result we find that the order parameter, which can show oscillatory or non-oscillatory dynamics, decays exponentially except for the effectively non-interacting case of the XX limit. For weakly ordered initial states we also find evidence for an algebraic correction to the exponential law. The study is based on numerical simulations using a numerical matrix product method for infinite system sizes (iMPS), for which we provide a detailed description and an error analysis. Additionally, we investigate in detail the exactly solvable XX limit. These results are compared to approximative analytical approaches including an effective description by the XZ-model as well as by mean-field, Luttinger-liquid and sine-Gordon theories. This reveals which aspects of non-equilibrium dynamics can as in equilibrium be described by low-energy theories and which are the novel phenomena specific to quantum quench dynamics. The relevance of the energetically high part of the spectrum is illustrated by means of a full numerical diagonalization of the Hamiltonian.

TL;DR: In this article, the authors considered impurities with two or more internal hyperfine states, and studied their radio-frequency (rf) absorption spectra, which correspond to transitions between two different hyper-fine states.

TL;DR: In this article, the authors use a nonperturbative renormalization group approach to develop a unified picture of the Bose polaron problem, where a mobile impurity is strongly interacting with a surrounding Bose-Einstein condensate (BEC).