77 research outputs found
Quench Dynamics in a Model with Tuneable Integrability Breaking
We consider quantum quenches in an integrable quantum chain with
tuneable-integrability-breaking interactions. In the case where these
interactions are weak, we demonstrate that at intermediate times after the
quench local observables relax to a prethermalized regime, which can be
described by a density matrix that can be viewed as a deformation of a
generalized Gibbs ensemble. We present explicit expressions for the
approximately conserved charges characterizing this ensemble. We do not find
evidence for a crossover from the prethermalized to a thermalized regime on the
time scales accessible to us. Increasing the integrability-breaking
interactions leads to a behaviour that is compatible with eventual
thermalization.Comment: 22 pages, 35 figures, minor updates to manuscrip
Comment on "Novel Superfluidity in a Trapped Gas of Fermi Atoms with Repulsive Interaction Loaded on an Optical Lattice"
In a recent letter Machida et al. [Phys. Rev. Lett. 93, 200402 (2004)]
concluded that in a trapped gas of fermions with repulsive interactions a
superfluid phase appears around the Mott-insulator at the center of the trap.
They base their conclusion on a negative binding energy, and a large weight for
a singlet formed by particles located at opposite sides of the Mott-insulator.
We show here that the observed effects are not related to superfluidity.Comment: Revtex file, 1 page, 1 figure, published versio
Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field
Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2
antiferromagnetic chain with alternating -tensor and Dzyaloshinskii-Moriya
interactions that exhibits a field-induced spin gap, are probed by means of
pulsed-field electron spin resonance spectroscopy. In particular, we report on
a minimum of the gap in the vicinity of the saturation field T
associated with a transition from the sine-Gordon region (with soliton-breather
elementary excitations) to a spin-polarized state (with magnon excitations).
This interpretation is fully confirmed by the quantitative agreement over the
entire field range of the experimental data with the DMRG investigation of the
spin-1/2 Heisenberg chain with a staggered transverse field
Topological invariants and interacting one-dimensional fermionic systems
We study one-dimensional, interacting, gapped fermionic systems described by
variants of the Peierls-Hubbard model and characterize their phases via a
topological invariant constructed out of their Green's functions. We
demonstrate that the existence of topologically protected, zero-energy states
at the boundaries of these systems can be tied to the values of their
topological invariant, just like when working with the conventional,
noninteracting topological insulators. We use a combination of analytical
methods and the numerical density matrix renormalization group method to
calculate the values of the topological invariant throughout the phase diagrams
of these systems, thus deducing when topologically protected boundary states
are present. We are also able to study topological states in spin systems
because, deep in the Mott insulating regime, these fermionic systems reduce to
spin chains. In this way, we associate the zero-energy states at the end of an
antiferromagnetic spin-one Heisenberg chain with the topological invariant 2.Comment: 15 pages, 11 figures, Final Version as published in PR
Melting of Discrete Vortices via Quantum Fluctuations
We consider nonlinear boson states with a nontrivial phase structure in the
three-site Bose-Hubbard ring, {\em quantum discrete vortices} (or {\em
q-vortices}), and study their "melting" under the action of quantum
fluctuations. We calculate the spatial correlations in the ground states to
show the superfluid-insulator crossover and analyze the fidelity between the
exact and variational ground states to explore the validity of the classical
analysis. We examine the phase coherence and the effect of quantum fluctuations
on q-vortices and reveal that the breakdown of these coherent structures
through quantum fluctuations accompanies the superfluid-insulator crossover.Comment: Revised version, 4 pages, 5 figures, Accepted for publication in
Physical Review Letter
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