391 research outputs found
Quantum phases of interacting bosons in optical lattices
This thesis presents a theoretical analysis of the phase diagram of ultracold bosons in a lattice and interacting with long-range interac- tions. The theoretical model is an extended Bose-Hubbard model and describes the dynamics of ultracold atoms in optical lattices realised in present experimental platforms. We consider here two situations, where either the long-range forces are global and emerge from the coupling with a high-finesse cavity, or they decay with the interparti- cle distance and can be due to Rydberg interactions or to the atoms permanent dipoles. We determine the ground state in one and two dimensions using mean-field treatments. In one dimension we comple- ment our studies using numerical programs based on tensor networks. We focus in particular on parameters for which the hopping induced by the kinetic energy competes with the interaction-induced corre- lated hopping between lattice sites. We analyse the superfluid phases emerging from the competition of these two mechanisms, and identify the parameters, where the two processes destructively interfere. For power-law interactions this quantum interference leads to insulating phases at relatively large kinetic energies, where one would otherwise expect superfluidity. When correlated tunnelling is due to the global potential of a resonator, the ground state is a self-organised topological insulator.Diese Arbeit präsentiert eine theoretische Analyse des Phasendiagramms von ultrakalten Bosonen in einem Gitter, die langreichweitige Wechselwirkungen erfahren. Das theoretische Modell ist ein erweitertes Bose-Hubbard Modell und beschreibt die Dynamik von ultrakalten Atomen in einem optischen Gitter, wie sie in heutigen Experimenten realisiert werden kann. Wir betrachten hier zwei Situationen: Zum einen sind die langreichweitigen Kräfte global und entstehen aus der Kopplung mit einem Resonator. Zum anderen zerfällt das Wechselwirkungspotential mit dem Abstand zwischen den Teilchen, wie es zwischen Rydbergatomen oder Atomen mit einem permanenten Dipolmoment auftritt. Wir bestimmen den Grundzustand in einer und zwei Dimensionen durch Mean-Field Analysen. In einer Dimension benutzen wir zudem ein auf Tensornetzwerken basierendes numerisches Programm. Wir betrachten insbesondere Parameter, für die das durch die kinetische Energie induzierte Tunneln mit dem von der Wechselwirkung induzierten Tunneln konkurriert. Wir analysieren die superfluiden Phasen, die sich aus dieser Kompetition ergeben, und identifizieren die Parameter, bei denen die beiden Prozesse destruktiv interferieren. Für die mit dem Abstand zerfallenden Wechselwirkungen führt diese Quanteninterferenz zu Isolatoren in Parameterbereichen, in denen man sonst Superfluidität erwarten würde. Wenn das Tunneln vom globalen Potential herrührt, ist der Grundzustand ein selbstorganisierter topologischer Isolator
Superfluid phases induced by the dipolar interactions
We determine the quantum ground state of dipolar bosons in a
quasi-one-dimensional optical lattice and interacting via -wave scattering.
The Hamiltonian is an extended Bose-Hubbard model which includes hopping terms
due to the interactions. We identify the parameter regime for which the
coefficients of the interaction-induced hopping terms become negative. For
these parameters we numerically determine the phase diagram for a canonical
ensemble and by means of density matrix renormalization group. We show that at
sufficiently large values of the dipolar strength there is a quantum
interference between the tunneling due to single-particle effects and the one
due to the interactions. Because of this phenomenon, incompressible phases
appear at relatively large values of the single-particle tunneling rates. This
quantum interference cuts the phase diagram into two different, disconnected
superfluid phases. In particular, at vanishing kinetic energy, the phase is
always superfluid with a staggered superfluid order parameter. These dynamics
emerge from quantum interference phenomena between quantum fluctuations and
interactions and shed light into their role in determining the thermodynamic
properties of quantum matter
Localization transition in presence of cavity backaction
We study the localization transition of an atom confined by an external
optical lattice in a high-finesse cavity. The atom-cavity coupling yields an
effective secondary lattice potential, whose wavelength is incommensurate with
the periodicity of the optical lattice. The cavity lattice can induce
localization of the atomic wave function analogously to the Aubry-Andr\'e
localization transition. Starting from the master equation for the cavity and
the atom we perform a mapping of the system dynamics to a Hubbard Hamiltonian,
which can be reduced to the Harper's Hamiltonian in appropriate limits. We
evaluate the phase diagram for the atom ground state and show that the
transition between extended and localized wavefunction is controlled by the
strength of the cavity nonlinearity, which determines the size of the localized
region and the behaviour of the Lyapunov exponent. The Lyapunov exponent, in
particular, exhibits resonance-like behaviour in correspondence with the
optomechanical resonances. Finally we discuss the experimental feasibility of
these predictions.Comment: 10 pages, 6 figure
Self-organized topological insulator due to cavity-mediated correlated tunneling
Topological materials have potential applications for quantum technologies.
Non-interacting topological materials, such as e.g., topological insulators and
superconductors, are classified by means of fundamental symmetry classes. It is
instead only partially understood how interactions affect topological
properties. Here, we discuss a model where topology emerges from the quantum
interference between single-particle dynamics and global interactions. The
system is composed by soft-core bosons that interact via global correlated
hopping in a one-dimensional lattice. The onset of quantum interference leads
to spontaneous breaking of the lattice translational symmetry, the
corresponding phase resembles nontrivial states of the celebrated
Su-Schriefer-Heeger model. Like the fermionic Peierls instability, the emerging
quantum phase is a topological insulator and is found at half fillings.
Originating from quantum interference, this topological phase is found in
"exact" density-matrix renormalization group calculations and is entirely
absent in the mean-field approach. We argue that these dynamics can be realized
in existing experimental platforms, such as cavity quantum electrodynamics
setups, where the topological features can be revealed in the light emitted by
the resonator.Comment: 10 pages, 7 figures, accepted in Quantu
Quantum critical behavior of entanglement in lattice bosons with cavity-mediated long-range interactions
We analyze the ground-state entanglement entropy of the extended Bose-Hubbard
model with infinite-range interactions. This model describes the low-energy
dynamics of ultracold bosons tightly bound to an optical lattice and
dispersively coupled to a cavity mode. The competition between onsite repulsion
and global cavity-induced interactions leads to a rich phase diagram, which
exhibits superfluid, supersolid, and insulating (Mott and checkerboard) phases.
We use a slave-boson treatment of harmonic quantum fluctuations around the
mean-field solution and calculate the entanglement entropy across the phase
transitions. At commensurate filling, the insulator-superfluid transition is
signalled by a singularity in the area-law scaling coefficient of the
entanglement entropy, that is similar to the one reported for the standard
Bose-Hubbard model. Remarkably, at the continuous
superfluid-to-supersolid transition we find a critical logarithmic term,
regardless of the filling. This behavior originates from the appearance of a
roton mode in the excitation and entanglement spectrum, becoming gapless at the
critical point, and it is characteristic of collective models.Comment: 19 pages, 4+9 figure
Staggered superfluid phases of dipolar bosons in two-dimensional square lattices
We study the quantum ground state of ultracold bosons in a two-dimensional
square lattice. The bosons interact via the repulsive dipolar interactions and
s-wave scattering. The dynamics is described by the extended Bose-Hubbard model
including correlated hopping due to the dipolar interactions, the coefficients
are found from the second quantized Hamiltonian using the Wannier expansion
with realistic parameters. We determine the phase diagram using the Gutzwiller
ansatz in the regime where the coefficients of the correlated hopping terms are
negative and can interfere with the tunneling due to single-particle effects.
We show that this interference gives rise to staggered superfluid and
supersolid phases at vanishing kinetic energy, while we identify parameter
regions at finite kinetic energy where the phases are incompressible. We
compare the results with the phase diagram obtained with the cluster Gutzwiller
approach and with the results found in one dimension using DMRG.Comment: version close to accepted in Phys. Rev.
Adult Zebrafish as a Model System for Cutaneous Wound-Healing Research
Upon injury, the skin must quickly regenerate to regain its barrier function. In mammals, wound healing is rapid and scar free during embryogenesis, whereas in adults it involves multiple steps including blood clotting, inflammation, re-epithelialization, vascularization, and granulation tissue formation and maturation, resulting in a scar. We have established a rapid and robust method to introduce full-thickness wounds onto the flank of adult zebrafish, and show that apart from external fibrin clot formation, all steps of adult mammalian wound repair also exist in zebrafish. Wound re-epithelialization is extremely rapid and initiates with no apparent lag phase, subsequently followed by the immigration of inflammatory cells and the formation of granulation tissue, consisting of macrophages, fibroblasts, blood vessels, and collagen. The granulation tissue later regresses, resulting in minimal scar formation. Studies after chemical treatment or with transgenic fish further suggest that wound re-epithelialization occurs independently of inflammation and fibroblast growth factor signaling, whereas both are essential for fibroblast recruitment and granulation tissue formation. Together, these results demonstrate that major steps and principles of cutaneous wound healing are conserved among adult mammals and adult zebrafish, making zebrafish a valuable model for studying vertebrate skin repair
Peliosis lienalis with atraumatic splenic rupture in a patient with chronic myelomonocytic leukemia: A case report.
INTRODUCTION
Atraumatic splenic rupture is a rare but life-threatening condition which may be associated with hematological malignancies.
PRESENTATION OF CASE
We present the case of a 63-year-old male patient with a history of chronic myelomonocytic leukemia and sarcoidosis under therapy with prednisone, who suffered an atraumatic splenic rupture with hemodynamic instability. He was managed with proximal splenic artery embolization and secondary open splenectomy. On pathology the diagnosis of peliosis lienalis was established.
DISCUSSION
Peliosis is a rare pathological entity, which presents with multiple blood-filled cavities within parenchymatous organs and is of unknown etiology and pathogenesis. In retrospect a rapid increase in splenomegaly and inhomogeneous parenchyma of the spleen on sonography was realized.
CONCLUSION
Sonographic changes in size and parenchyma of the spleen in patients with hematological malignancies might help suspecting peliosis lienalis with impending splenic rupture and could alter clinical management towards a prophylactic splenectomy
Recommendations for increasing research on co-occurring serious mental illness and gambling problems : Commentary on: Disordered gambling and psychosis: Prevalence and clinical correlates (Cassetta et al., 2018)
Psychiatric disorders frequently co-occur with gambling disorder. Although community and clinical samples show frequent co-occurrence between gambling and psychotic disorders, relatively little research has been conducted on this population. Here, we comment on a recent study conducted in Brazil on the clinical correlates of psychotic disorders in treatment-seeking individuals with gambling disorder, relate the findings to those from the northeastern region of the United States, and discuss implications with respect to promoting responsible gambling in the setting of the expansion of legalized gambling
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