Relaxation of Phonons in the Lieb-Liniger Gas by Dynamical Refermionization.

Motivated by recent experiments, we investigate the Lieb-Liniger gas initially prepared in an out-of-equilibrium state that is Gaussian in terms of the phonons, namely whose density matrix is the exponential of an operator quadratic in terms of phonon creation and annihilation operators. Because the phonons are not exact eigenstates of the Hamiltonian, the gas relaxes to a stationary state at very long times whose phonon population is a priori different from the initial one. Thanks to integrability, that stationary state needs not be a thermal state.

Generalized hydrodynamics in strongly interacting 1D Bose gases.

The dynamics of strongly interacting many-body quantum systems are notoriously complex and difficult to simulate. A recently proposed theory called generalized hydrodynamics (GHD) promises to efficiently accomplish such simulations for nearly integrable systems. We test GHD with bundles of ultracold one-dimensional (1D) Bose gases by performing large trap quenches in both the strong and intermediate coupling regimes.

Quantum Generalized Hydrodynamics.

Physical systems made of many interacting quantum particles can often be described by Euler hydrodynamic equations in the limit of long wavelengths and low frequencies. Recently such a classical hydrodynamic framework, now dubbed generalized hydrodynamics (GHD), was found for quantum integrable models in one spatial dimension. Despite its great predictive power, GHD, like any Euler hydrodynamic equation, misses important quantum effects, such as quantum fluctuations leading to nonzero equal-time correlations between fluid cells at different positions.

Large-Scale Description of Interacting One-Dimensional Bose Gases: Generalized Hydrodynamics Supersedes Conventional Hydrodynamics.

The theory of generalized hydrodynamics (GHD) was recently developed as a new tool for the study of inhomogeneous time evolution in many-body interacting systems with infinitely many conserved charges. In this Letter, we show that it supersedes the widely used conventional hydrodynamics (CHD) of one-dimensional Bose gases. We illustrate this by studying "nonlinear sound waves" emanating from initial density accumulations in the Lieb-Liniger model.

Exact solution of the anisotropic special transition in the O(n) model in two dimensions.

The effect of surface exchange anisotropies is known to play an important role in magnetic critical and multicritical behavior at surfaces. We give an exact analysis of this problem in d=2 for the O(n) model using the Coulomb gas, conformal invariance, and integrability techniques. We obtain the full set of critical exponents at the anisotropic special transition-where the symmetry on the boundary is broken down to O(n1)xO(n-n1)--as a function of n1.