1,745 research outputs found
A continuous-time solver for quantum impurity models
We present a new continuous time solver for quantum impurity models such as
those relevant to dynamical mean field theory. It is based on a stochastic
sampling of a perturbation expansion in the impurity-bath hybridization
parameter. Comparisons to quantum Monte Carlo and exact diagonalization
calculations confirm the accuracy of the new approach, which allows very
efficient simulations even at low temperatures and for strong interactions. As
examples of the power of the method we present results for the temperature
dependence of the kinetic energy and the free energy, enabling an accurate
location of the temperature-driven metal-insulator transition.Comment: Published versio
Quantum Phase Transitions in Coupled Dimer Compounds
We study the critical properties in cubic systems of antiferromagnetically
coupled spin dimers near magnetic-field induced quantum phase transitions. The
quantum critical points in the zero-temperature phase diagrams are determined
from quantum Monte Carlo simulations. Furthermore, scaling properties of the
uniform magnetization and the staggered transverse magnetization across the
quantum phase transition in magnetic fields are calculated. The critical
exponents are derived from Ginzburg-Landau theory. We find excellent agreement
between the quantum Monte Carlo simulations and the analytical results.Comment: 7 pages, 9 eps-figure
Thermalization of strongly interacting bosons after spontaneous emissions in optical lattices
We study the out-of-equilibrium dynamics of bosonic atoms in a 1D optical
lattice, after the ground-state is excited by a single spontaneous emission
event, i.e. after an absorption and re-emission of a lattice photon. This is an
important fundamental source of decoherence for current experiments, and
understanding the resulting dynamics and changes in the many-body state is
important for controlling heating in quantum simulators. Previously it was
found that in the superfluid regime, simple observables relax to values that
can be described by a thermal distribution on experimental time-scales, and
that this breaks down for strong interactions (in the Mott insulator regime).
Here we expand on this result, investigating the relaxation of the momentum
distribution as a function of time, and discussing the relationship to
eigenstate thermalization. For the strongly interacting limit, we provide an
analytical analysis for the behavior of the system, based on an effective
low-energy Hamiltonian in which the dynamics can be understood based on
correlated doublon-holon pairs.Comment: 8 pages, 5 figure
Discerning Incompressible and Compressible Phases of Cold Atoms in Optical Lattices
Experiments with cold atoms trapped in optical lattices offer the potential
to realize a variety of novel phases but suffer from severe spatial
inhomogeneity that can obscure signatures of new phases of matter and phase
boundaries. We use a high temperature series expansion to show that
compressibility in the core of a trapped Fermi-Hubbard system is related to
measurements of changes in double occupancy. This core compressibility filters
out edge effects, offering a direct probe of compressibility independent of
inhomogeneity. A comparison with experiments is made
Efficient DMFT-simulation of the Holstein-Hubbard Model
We present a method for solving impurity models with electron-phonon
coupling, which treats the phonons efficiently and without approximations. The
algorithm is applied to the Holstein-Hubbard model in the dynamical mean field
approximation, where it allows access to strong interactions, very low
temperatures and arbitrary fillings. We show that a renormalized
Migdal-Eliashberg theory provides a reasonlable description of the phonon
contribution to the electronic self energy in strongly doped systems, but fails
if the quasiparticle energy becomes of order of the phonon frequency.Comment: Published versio
Quench dynamics and non equilibrium phase diagram of the Bose-Hubbard model
We investigate the time evolution of correlations in the Bose-Hubbard model
following a quench from the superfluid to the Mott insulating phase. For large
values of the final interaction strength the system approaches a distinctly
non-equilibrium steady state that bears strong memory of the initial
conditions. In contrast, when the final interaction strength is comparable to
the hopping, the correlations are rather well approximated by those at thermal
equilibrium. The existence of two distinct non-equilibrium regimes is
surprising given the non-integrability of the Bose-Hubbard model. We relate
this phenomena to the role of quasi-particle interactions in the Mott
insulating state
Supersolid phase induced by correlated hopping in spin-1/2 frustrated quantum magnets
We show that correlated hopping of triplets, which is often the dominant
source of kinetic energy in dimer-based frustrated quantum magnets, produces a
remarkably strong tendency to form supersolid phases in a magnetic field. These
phases are characterized by simultaneous modulation and ordering of the
longitudinal and transverse magnetization respectively. Using Quantum Monte
Carlo and a semiclassical approach for an effective hard-core boson model with
nearest-neighbor repulsion on a square lattice, we prove in particular that a
supersolid phase can exist even if the repulsion is not strong enough to
stabilize an insulating phase at half-filling. Experimental implications for
frustrated quantum antiferromagnets in a magnetic field at zero and finite
temperature are discussed.Comment: 4 pages; 4 figures; published versio
A supersymmetric multicritical point in a model of lattice fermions
We study a model of spinless fermions with infinite nearest-neighbor
repulsion on the square ladder which has microscopic supersymmetry. It has been
conjectured that in the continuum the model is described by the superconformal
minimal model with central charge c=3/2. Thus far it has not been possible to
confirm this conjecture due to strong finite-size corrections in numerical
data. We trace the origin of these corrections to the presence of unusual
marginal operators that break Lorentz invariance, but preserve part of the
supersymmetry. By relying mostly on entanglement entropy calculations with the
density-matrix renormalization group, we are able to reduce finite-size effects
significantly. This allows us to unambiguously determine the continuum theory
of the model. We also study perturbations of the model and establish that the
supersymmetric model is a multicritical point. Our work underlines the power of
entanglement entropy as a probe of the phases of quantum many-body systems.Comment: 16 pages, 8 figure
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