82 research outputs found
Equilibrium phases of dipolar lattice bosons in the presence of random diagonal disorder
Ultracold gases offer an unprecedented opportunity to engineer disorder and
interactions in a controlled manner. In an effort to understand the interplay
between disorder, dipolar interaction and quantum degeneracy, we study
two-dimensional hard-core dipolar lattice bosons in the presence of on-site
bound disorder. Our results are based on large-scale path-integral quantum
Monte Carlo simulations by the Worm algorithm. We study the ground state phase
diagram at fixed half-integer filling factor for which the clean system is
either a superfluid at lower dipolar interaction strength or a checkerboard
solid at larger dipolar interaction strength. We find that, even for weak
dipolar interaction, superfluidity is destroyed in favor of a Bose glass at
relatively low disorder strength. Interestingly, in the presence of disorder,
superfluidity persists for values of dipolar interaction strength for which the
clean system is a checkerboard solid. At fixed disorder strength, as the
dipolar interaction is increased, superfluidity is destroyed in favor of a Bose
glass. As the interaction is further increased, the system eventually develops
extended checkerboard patterns in the density distribution. Due to the presence
of disorder, though, grain boundaries and defects, responsible for a finite
residual compressibility, are present in the density distribution. Finally, we
study the robustness of the superfluid phase against thermal fluctuations
Equilibrium Phases of Tilted Dipolar Lattice Bosons
The recent advances in creating nearly degenerate quantum dipolar gases in
optical lattices are opening the doors for the exploration of equilibrium
physics of quantum systems with anisotropic and long-range dipolar
interactions. In this paper we study the zero- and finite-temperature phase
diagrams of a system of hard-core dipolar bosons at half-filling, trapped in a
two-dimensional optical lattice. The dipoles are aligned parallel to one
another and tilted out of the optical lattice plane by means of an external
electric field. At zero-temperature, the system is a superfluid at all tilt
angles provided that the strength of dipolar interaction is below a
critical value . Upon increasing the interaction strength while
keeping fixed, the superfluid phase is destabilized in favor of a
checkerboard or a stripe solid depending on the tilt angle. We explore the
nature of the phase transition between the two solid phases and find evidence
of a micro-emulsion phase, following the Spivak-Kivelson scenario, separating
these two solid phases. Additionally, we study the stability of these quantum
phases against thermal fluctuations and find that the stripe solid is the most
robust, making it the best candidate for experimental observation.Comment: 7 pages, 6 figure
Quantum phases of hard-core dipolar bosons in coupled one-dimensional optical lattices
Hard-core dipolar bosons trapped in a parallel stack of N ≥ 2 one-dimensional optical lattices (tubes) can develop several phases made of composites of particles from different tubes: superfluids, supercounterfluids, and insulators as well as mixtures of those. Bosonization analysis shows that these phases are thresholdless with respect to the dipolar interaction, with the key “control knob” being filling factors in each tube, provided the intertube tunneling is suppressed. The effective ab initio quantum Monte Carlo algorithm capturing these phases is introduced and some results are presented.National Science Foundation (U.S.) (Grant CNS-0855217)National Science Foundation (U.S.) (Grant CNS-0958379)National Science Foundation (U.S.) (Grant ACI-1126113
Superfluid-Insulator and Roughening Transitions in Domain Walls
We have performed quantum Monte Carlo simulations to investigate the
superfluid behavior of one- and two-dimensional interfaces separating
checkerboard solid domains. The system is described by the hard-core
Bose-Hubbard Hamiltonian with nearest-neighbor interaction. In accordance with
Ref.1, we find that (i) the interface remains superfluid in a wide range of
interaction strength before it undergoes a superfluid-insulator transition;
(ii) in one dimension, the transition is of the Kosterlitz-Thouless type and is
accompanied by the roughening transition, driven by proliferation of charge 1/2
quasiparticles; (iii) in two dimensions, the transition belongs to the 3D U(1)
universality class and the interface remains smooth. Similar phenomena are
expected for domain walls in quantum antiferromagnets.Comment: 6 pages, 7 figures; references added, typo corrected in fig
Multiworm algorithm quantum Monte Carlo
We review the path-integral quantum Monte Carlo method and discuss its
implementation by multiworm algorithms. We analyze in details the features of
the algorithms, and focus our attention on the computation of the -body
density matrix to study N-body correlations. Finally, we demonstrate the
validity of the algorithms on a system of dipolar bosons trapped in a stack of
one-dimensional layers in the case of zero and finite inter-layer hopping.Comment: 20 pages, 10 figure
First order phase transitions in optical lattices with tunable three-body onsite interaction
We study the two-dimensional Bose-Hubbard model in the presence of a
three-body interaction term, both at a mean field level and via quantum Monte
Carlo simulations. The three-body term is tuned by coupling the triply occupied
states to a trapped universal trimer. We find that, for sufficiently attractive
three-body interaction the n = 2 Mott lobe disappears and the system displays
first order phase transitions separating the n = 1 from the n = 3 lobes, and
the n = 1 and n = 3 Mott insulator from the superfluid. We have also analyzed
the effect of finite temperature and found that transitions are still of first
order at temperatures T\simJ where J is the hopping matrix element.Comment: introduction slightly changed, modified figure
Adverse reactions to oncologic drugs: spontaneous reporting and signal detection
Oncology is one of the areas of medicine with the most active research being conducted on new drugs. New pharmacological entities frequently enter the clinical arena, and therefore, the safety profile of anticancer products deserves continuous monitoring. However, only very severe and (unusual) suspected adverse drug reactions (ADRs) are usually reported, since cancer patients develop ADRs very frequently and some practical selectivity must be used. Notably, a recent study was able to identify 76 serious ADRs reported in updated drug labels of oncologic drugs and 50% of them (n = 38) were potentially fatal. Of these, 49 and 58%, respectively, were not described in initial drug labels. The aims of this article are to provide an overview about spontaneous reporting of ADRs of oncologic drugs and to discuss the available methods to analyze the safety of anticancer drugs using databases of spontaneous ADR reporting
Quantum Phases of Cold Polar Molecules in 2D Optical Lattices
We discuss the quantum phases of hard-core bosons on a two-dimensional square
lattice interacting via repulsive dipole-dipole interactions, as realizable
with polar molecules trapped in optical lattices. In the limit of small
tunneling, we find evidence for a devil's staircase, where solid phases appear
at all rational fillings of the underlying lattice. For finite tunneling, we
establish the existence of extended regions of parameters where the groundstate
is a supersolid, obtained by doping the solids either with particles or
vacancies. Here the solid-superfluid quantum melting transition consists of two
consecutive second-order transitions, with a supersolid as the intermediate
phase. The effects of finite temperature and confining potentials relevant to
experiments are discussed.Comment: replaced with published versio
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