655 research outputs found
Absence of a Direct Superfluid to Mott Insulator Transition in Disordered Bose Systems
We prove the absence of a direct quantum phase transition between a
superfluid and a Mott insulator in a bosonic system with generic, bounded
disorder. We also prove compressibility of the system on the
superfluid--insulator critical line and in its neighborhood. These conclusions
follow from a general {\it theorem of inclusions} which states that for any
transition in a disordered system one can always find rare regions of the
competing phase on either side of the transition line. Quantum Monte Carlo
simulations for the disordered Bose-Hubbard model show an even stronger result,
important for the nature of the Mott insulator to Bose glass phase transition:
The critical disorder bound, , corresponding to the onset of
disorder-induced superfluidity, satisfies the relation , with the half-width of the Mott gap in the pure system.Comment: 4 pages, 3 figures; replaced with resubmitted versio
Criticality in Trapped Atomic Systems
We discuss generic limits posed by the trap in atomic systems on the accurate
determination of critical parameters for second-order phase transitions, from
which we deduce optimal protocols to extract them. We show that under current
experimental conditions the in-situ density profiles are barely suitable for an
accurate study of critical points in the strongly correlated regime. Contrary
to recent claims, the proper analysis of time-of-fight images yields critical
parameters accurately.Comment: 4 pages, 3 figures; added reference
Comment on "Direct Mapping of the Finite Temperature Phase Diagram of Strongly Correlated Quantum Models" by Q. Zhou, Y. Kato, N. Kawashima, and N. Trivedi, Phys. Rev. Lett. 103, 085701 (2009)
In their Letter, Zhou, Kato, Kawashima, and Trivedi claim that
finite-temperature critical points of strongly correlated quantum models
emulated by optical lattice experiments can generically be deduced from kinks
in the derivative of the density profile of atoms in the trap with respect to
the external potential, . In this comment we demonstrate
that the authors failed to achieve their goal: to show that under realistic
experimental conditions critical densities can be extracted from
density profiles with controllable accuracy.Comment: 1 page, 1 figur
Grounding the data. A response to: Population finiteness is not a concern for null hypothesis significance testing when studying human behavior
A commentary on
Population finiteness is not a concern for null hypothesis significance testing when studying human behavior. A reply to Pollet (2013)
by Quillien, T. (2015). Front. Neurosci. 9:81. doi: 10.3389/fnins.2015.0008
Disorder-induced superfluidity
We use quantum Monte Carlo simulations to study the phase diagram of
hard-core bosons with short-ranged {\it attractive} interactions, in the
presence of uniform diagonal disorder. It is shown that moderate disorder
stabilizes a glassy superfluid phase in a range of values of the attractive
interaction for which the system is a Mott insulator, in the absence of
disorder. A transition to an insulating Bose glass phase occurs as the strength
of the disorder or interactions increases.Comment: 5 pages, 6 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
Regularization of Diagrammatic Series with Zero Convergence Radius
The divergence of perturbative expansions for the vast majority of
macroscopic systems, which follows from Dyson's collapse argument, prevents
Feynman's diagrammatic technique from being directly used for controllable
studies of strongly interacting systems. We show how the problem of divergence
can be solved by replacing the original model with a convergent sequence of
successive approximations which have a convergent perturbative series. As a
prototypical model, we consider the zero-dimensional
theory.Comment: 4 pages, 3 figure
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