Tuning the dipolar interaction in quantum gases

We have studied the tunability of the interaction between permanent dipoles in Bose-Einstein condensates. Based on time-dependent control of the anisotropy of the dipolar interaction, we show that even the very weak magnetic dipole coupling in alkali gases can be used to excite collective modes. Furthermore, we discuss how the effective dipolar coupling in a Bose-Einstein condensate can be tuned from positive to negative values and even switched off completely by fast rotation of the orientation of the dipoles.Comment: 4 pages, 3 figures. Submitted to PRL. (v3: Figure 3 replaced

Exact hydrodynamics of a trapped dipolar Bose-Einstein condensate

We derive the exact density profile of a harmonically trapped Bose-Einstein condensate (BEC) which has dipole-dipole interactions as well as the usual s-wave contact interaction, in the Thomas-Fermi limit. Remarkably, despite the non-local anisotropic nature of the dipolar interaction, the density turns out to be an inverted parabola, just as in the pure s-wave case, but with a modified aspect ratio. The ``scaling'' solution approach of Kagan, Surkov, and Shlyapnikov [Phys. Rev. A 54, 1753 (1996)] and Castin and Dum [Phys. Rev. Lett. 77}, 5315 (1996)] for a BEC in a time-dependent trap can therefore be applied to a dipolar BEC, and we use it to obtain the exact monopole and quadrupole shape oscillation frequencies.Comment: 5 pages, 3 figure

Entanglement Entropy and Mutual Information Production Rates in Acoustic Black Holes

A method to investigate acoustic Hawking radiation is proposed, where entanglement entropy and mutual information are measured from the fluctuations of the number of particles. The rate of entropy radiated per one-dimensional (1D) channel is given by $\dot{S}=\kappa/12$, where $\kappa$ is the sound acceleration on the sonic horizon. This entropy production is accompanied by a corresponding formation of mutual information to ensure the overall conservation of information. The predictions are confirmed using an \emph{ab initio} analytical approach in transonic flows of 1D degenerate ideal Fermi fluids.Comment: 4 pages, 1 figure. Supplemental Material (pdf) included in the source of this manuscrip

Comparing contact and dipolar interaction in a Bose-Einstein condensate

We have measured the relative strength $\epsilon_dd$ of the magnetic dipole-dipole interaction compared to the contact interaction in a chromium Bose-Einstein condensate. We analyze the asymptotic velocities of expansion of a dipolar chromium BEC with different orientations of the atomic magnetic dipole moments. By comparing them with numerical solutions of the hydrodynamic equations for dipolar condensates, we are able to determine $\epsilon_dd = 0.159\pm0.034$ with high accuracy. Since the absolute strength of the dipole-dipole interaction is known exactly, the relative strength of the dipoledipole interaction can be used to determine the s-wave scattering length $a = 5.08\pm1.06\cdot10^-9 m = 96\pm20 a0$ of 52Cr. This is fully consistent with our previous measurements on the basis of Feshbach resonances

Strong dipolar effects in a quantum ferrofluid

We report on the realization of a Chromium Bose-Einstein condensate (BEC) with strong dipolar interaction. By using a Feshbach resonance, we reduce the usual isotropic contact interaction, such that the anisotropic magnetic dipole-dipole interaction between 52Cr atoms becomes comparable in strength. This induces a change of the aspect ratio of the cloud, and, for strong dipolar interaction, the inversion of ellipticity during expansion - the usual "smoking gun" evidence for BEC - can even be suppressed. These effects are accounted for by taking into account the dipolar interaction in the superfluid hydrodynamic equations governing the dynamics of the gas, in the same way as classical ferrofluids can be described by including dipolar terms in the classical hydrodynamic equations. Our results are a first step in the exploration of the unique properties of quantum ferrofluids.Comment: Final, published versio

On an exact solution of the Thomas-Fermi equation for a trapped Bose-Einstein condensate with dipole-dipole interactions

We derive an exact solution to the Thomas-Fermi equation for a Bose-Einstein condensate which has dipole-dipole interactions as well as the usual s-wave contact interaction, in a harmonic trap. Remarkably, despite the non-local anisotropic nature of the dipolar interaction the solution is an inverted parabola, as in the pure s-wave case, but with a different aspect ratio. Various properties such as electrostriction and stability are discussed.Comment: 11 pages, 5 figure

\u201cShould I stay or Should I go\u201d: patient who leave Emergency Department of an Italian Third-Level Teaching Hospital

Background and Aim: Patients could leave ED not receiving the desired care either Without Being Seen by a doctor (LWBS) or Against Medical Advice (DAMA). In term of care quality, LWBS may be related to inappropriate access and process of care, while DAMA may lead to increased risk of mortality and re-admissions. This study aims to identify frequency of patients who leave ED, determine their characteristics and identify associated factor. Methods: This was a retrospective observational study of patients that attended EDs of University Hospital Trust of Verona in 2017. Demographic and ED access associated variables were collected for LWBS, DAMA and completed-ED-treatment patients. Univariate and multivariate data analyses was based on EMUR-PS administrative data. Results: 5,901 of 127,180 ED accesses were uncompleted treatment (4.64%); LWBS were 4,664 (79.04%) and DAMA 1,237 (20.96%). Those who leave ED tended to be younger (39.35 vs. 45.56, p<0.01). Independent factors associated with ED leaving resulted: i) nonurgent triage category (OR: 2.941, 95%CI: 2.405-3.596) ii) non-Italian-nationality (OR: 1.695, 95%CI: 1.493-1.924) and requiring psychiatric consult (OR:6.16 95%IC 4.82-7.87); while protective factors resulted: i) female gender (OR: 0.713, 95%CI: 0.633-0.803); i) Paediatric ED (OR: 0.593, 95%CI: 0.437-0.805); ii) Obstetrics-Gynaecology ED (OR: 0.284, 95%CI: 0.193-0.416) iii) inclusion in fast track pathways (OR: 0.747, 95%CI: 0.602-0.927). Higher ED leaving rate were observed during night-time and Sunday, either overcrowding resulted not associated.Conclusion: Results show the necessity to implement primary care-ED integrated pathway, mainly in frail sub-population, improve awareness on healthcare service use and refine communication skills in ED-team

Risk of Symptomatic Infection During a Second Coronavirus Disease 2019 Wave in Severe Acute Respiratory Syndrome Coronavirus 2–Seropositive Individuals

We analyzed 221 COVID-19 cases identified between June 2020 and January 2021 in 6,074 individuals screened for IgG antibodies in May 2020, representing 77% of residents of five Italian municipalities. The adjusted relative risk of developing symptomatic infection in SARS-COV-2 seropositive participants was 0.055 (95%CI: 0.014 - 0.220)