36,220 research outputs found
Non-Gaussian distribution of collective operators in quantum spin chains
We numerically analyse the behavior of the full distribution of collective
observables in quantum spin chains. While most of previous studies of quantum
critical phenomena are limited to the first moments, here we demonstrate how
quantum fluctuations at criticality lead to highly non-Gaussian distributions
thus violating the central limit theorem. Interestingly, we show that the
distributions for different system sizes collapse after scaling on the same
curve for a wide range of transitions: first and second order quantum
transitions and transitions of the Berezinskii-Kosterlitz-Thouless type. We
propose and carefully analyse the feasibility of an experimental reconstruction
of the distribution using light-matter interfaces for atoms in optical lattices
or in optical resonators.Comment: 15 pages, 5 figures; last version close to published versio
Broadening of HO rotational lines by collision with He atoms at low temperature
We report pressure broadening coefficients for the 21 electric-dipole
transitions between the eight lowest rotational levels of ortho-HO and
para-HO molecules by collisions with He at temperatures from 20 to 120 K.
These coefficients are derived from recently published experimental
state-to-state rate coefficients for HO:He inelastic collisions, plus an
elastic contribution from close coupling calculations. The resulting
coefficients are compared to the available experimental data. Mostly due to the
elastic contribution, the pressure broadening coefficients differ much from
line to line, and increase markedly at low temperature. The present results are
meant as a guide for future experiments and astrophysical observations.Comment: 2 figures, 2 table
The Bose-Hubbard model on a triangular lattice with diamond ring-exchange
Ring-exchange interactions have been proposed as a possible mechanism for a
Bose-liquid phase at zero temperature, a phase that is compressible with no
superfluidity. Using the Stochastic Green Function algorithm (SGF), we study
the effect of these interactions for bosons on a two-dimensional triangular
lattice. We show that the supersolid phase, that is known to exist in the
ground state for a wide range of densities, is rapidly destroyed as the
ring-exchange interactions are turned on. We establish the ground-state phase
diagram of the system, which is characterized by the absence of the expected
Bose-liquid phase.Comment: 6 pages, 10 figure
Entanglement properties of spin models in triangular lattices
The different quantum phases appearing in strongly correlated systems as well
as their transitions are closely related to the entanglement shared between
their constituents. In 1D systems, it is well established that the entanglement
spectrum is linked to the symmetries that protect the different quantum phases.
This relation extends even further at the phase transitions where a direct link
associates the entanglement spectrum to the conformal field theory describing
the former. For 2D systems much less is known. The lattice geometry becomes a
crucial aspect to consider when studying entanglement and phase transitions.
Here, we analyze the entanglement properties of triangular spin lattice models
by considering also concepts borrowed from quantum information theory such as
geometric entanglement.Comment: 19 pages, 8 figure
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