399 research outputs found
Relaxation and thermalization in the one-dimensional Bose-Hubbard model: A case study for the interaction quantum quench from the atomic limit
Motivated by recent experiments, we study the relaxation dynamics and
thermalization in the one-dimensional Bose-Hubbard model induced by a global
interaction quench. Specifically, we start from an initial state that has
exactly one boson per site and is the ground state of a system with infinitely
strong repulsive interactions at unit filling. Using exact diagonalization and
the density matrix renormalization group method, we compute the time dependence
of such observables as the multiple occupancy and the momentum distribution
function. Typically, the relaxation to stationary values occurs over just a few
tunneling times. The stationary values are identical to the so-called diagonal
ensemble on the system sizes accessible to our numerical methods and we further
observe that the micro-canonical ensemble describes the steady state of many
observables reasonably well for small and intermediate interaction strength.
The expectation values of observables in the canonical ensemble agree
quantitatively with the time averages obtained from the quench at small
interaction strengths, and qualitatively provide a good description of
steady-state values even in parameter regimes where the micro-canonical
ensemble is not applicable due to finite-size effects. We discuss our numerical
results in the framework of the eigenstate thermalization hypothesis. Moreover,
we also observe that the diagonal and the canonical ensemble are practically
identical for our initial conditions already on the level of their respective
energy distributions for small interaction strengths. Finally, we discuss
implications of our results for the interpretation of a recent sudden expansion
experiment [Phys. Rev. Lett. 110, 205301 (2013)], in which the same interaction
quench was realized.Comment: 19 pages, 22 figure
Nonequilibrium propagation and decay of a bound pair in driven t-J models
We perform an accurate time-dependent numerical study of out-of-equilibrium
response of a bound state within t-J systems on a two-leg ladder and a square
lattice. We show that the bound hole pair decays with the onset of finite
steady current if both mechanisms for binding and the dissipation share
matching degrees of freedom. Moreover, by investigating the mechanism of decay
on the square lattice we find that the dynamics is governed by the decay in the
direction perpendicular to the electric field, leading to much shorter decay
times in comparison to the ladder where such dynamics is topologically
restricted
Average eigenstate entanglement entropy of the XY chain in a transverse field and its universality for translationally invariant quadratic fermionic models
Effective approach to the Nagaoka regime of the two dimensional t-J model
We argue that the t-J model and the recently proposed Ising version of this
model give the same physical picture of the Nagaoka regime for J/t << 1. In
particular, both models are shown to give compatible results for a single
Nagaoka polaron as well as for a Nagaoka bipolaron. When compared to the
standard t-J or t-Jz models, the Ising version allows for a numerical analysis
on much larger clusters by means of classical Monte Carlo simulations. Taking
the advantage of this fact, we study the low doping regime of t-J model for J/t
<< 1 and show that the ground state exhibits phase separation into hole-rich
ferromagnetic and hole-depleted antiferromagnetic regions. This picture holds
true up to a threshold concentration of holes, \delta < \delta_t ~ 0.44
\sqrt{J/t}. Analytical calculations show that \delta_t=\sqrt{J/2\pi t}.Comment: 10 pages, 10 figures, revte
Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta
Long-range order in quantum many-body systems is usually associated with
equilibrium situations. Here, we experimentally investigate the
quasicondensation of strongly-interacting bosons at finite momenta in a
far-from-equilibrium case. We prepare an inhomogeneous initial state consisting
of one-dimensional Mott insulators in the center of otherwise empty
one-dimensional chains in an optical lattice with a lattice constant . After
suddenly quenching the trapping potential to zero, we observe the onset of
coherence in spontaneously forming quasicondensates in the lattice. Remarkably,
the emerging phase order differs from the ground-state order and is
characterized by peaks at finite momenta in the
momentum distribution function.Comment: See also Viewpoint: Emerging Quantum Order in an Expanding Gas,
Physics 8, 99 (2015
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