Groundstates of SU(2)-Symmetric Confined Bose Gas: Trap for a Schr\"odinger Cat

Conservation of the total isotopic spin S of a two-component Bose gas-like $^{87}$Rb-has a dramatic impact on the structure of the ground state. In the case when S is much smaller than the total number of particles N, the condensation of each of the two components occurs into two single-particle modes. The quantum wavefunction of such a groundstate is a Schr\"odinger Cat-a superposition of the phase separated classical condensates, the most "probable" state in the superposition corresponding to the classical groundstate in the sector of given N and S. After measurement of the spatial distribution of the densities of the two components, the Cat collapses into one of the classical condensate states.Comment: 5 RevTex pages, no figures; replaced with revised version, where the discussion on stability against temporal white noise and losses is adde

Diagrammatic Monte Carlo for Correlated Fermions

We show that Monte Carlo sampling of the Feynman diagrammatic series (DiagMC) can be used for tackling hard fermionic quantum many-body problems in the thermodynamic limit by presenting accurate results for the repulsive Hubbard model in the correlated Fermi liquid regime. Sampling Feynman's diagrammatic series for the single-particle self-energy we can study moderate values of the on-site repulsion ($U/t \sim 4$) and temperatures down to $T/t=1/40$. We compare our results with high temperature series expansion and with single-site and cluster dynamical mean-field theory.Comment: 4 pages, 5 figures, stylistic change

Fluctuating and dissipative dynamics of dark solitons in quasi-condensates

The fluctuating and dissipative dynamics of matter-wave dark solitons within harmonically trapped, partially condensed Bose gases is studied both numerically and analytically. A study of the stochastic Gross-Pitaevskii equation, which correctly accounts for density and phase fluctuations at finite temperatures, reveals dark soliton decay times to be lognormally distributed at each temperature, thereby characterizing the previously predicted long lived soliton trajectories within each ensemble of numerical realizations (S.P. Cockburn {\it et al.}, Phys. Rev. Lett. 104, 174101 (2010)). Expectation values for the average soliton lifetimes extracted from these distributions are found to agree well with both numerical and analytic predictions based upon the dissipative Gross-Pitaevskii model (with the same {\it ab initio} damping). Probing the regime for which $0.8 k_{B}T < \mu < 1.6 k_{B}T$, we find average soliton lifetimes to scale with temperature as $\tau\sim T^{-4}$, in agreement with predictions previously made for the low-temperature regime $k_{B}T\ll\mu$. The model is also shown to capture the experimentally-relevant decrease in the visibility of an oscillating soliton due to the presence of background fluctuations.Comment: 17 pages, 14 figure

The effect of light assisted collisions on matter wave coherence in superradiant Bose-Einstein condensates

We investigate experimentally the effects of light assisted collisions on the coherence between momentum states in Bose-Einstein condensates. The onset of superradiant Rayleigh scattering serves as a sensitive monitor for matter wave coherence. A subtle interplay of binary and collective effects leads to a profound asymmetry between the two sides of the atomic resonance and provides far bigger coherence loss rates for a condensate bathed in blue detuned light than previously estimated. We present a simplified quantitative model containing the essential physics to explain our experimental data and point at a new experimental route to study strongly coupled light matter systems.Comment: 10 pages, 4 figure

Observation of vortex dipoles in an oblate Bose-Einstein condensate

We report experimental observations and numerical simulations of the formation, dynamics, and lifetimes of single and multiply charged quantized vortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We nucleate pairs of vortices of opposite charge (vortex dipoles) by forcing superfluid flow around a repulsive gaussian obstacle within the BEC. By controlling the flow velocity we determine the critical velocity for the nucleation of a single vortex dipole, with excellent agreement between experimental and numerical results. We present measurements of vortex dipole dynamics, finding that the vortex cores of opposite charge can exist for many seconds and that annihilation is inhibited in our highly oblate trap geometry. For sufficiently rapid flow velocities we find that clusters of like-charge vortices aggregate into long-lived dipolar flow structures.Comment: 4 pages, 4 figures, 1 EPAPS fil

Желчнокаменная болезнь среди медицинского персонала поликлиники: факторы риска ее развития в разных профессиональных группах

The aim. Identification of risk factors for gallstone disease (GDS) development between different professional groups of polyclinic medical staff. Material and methods. 75 medical staff members were divided into two groups (1st group: 30 doctors; 2nd group: 45 nurses). All of them were interviewed fo r information about profession, gender, age, waist circumference (WC), body mass index (BMI), smoking, arterial hypertension (AH), diabetes mellitus (DM) and hypercholesterolemia. In addition, women were interviewed about the number of pregnancies, ostmenopause and taking oral contraceptive pills (OCPs). To assess physical activity, a short international questionnaire on physical activity (IPAQ) was used. To identify the presence of professional burnout (PB) syndrome we applied the Maslach Burnout Inventory (MBI) questionnaire, adapted by N.Е. Vodopianova for medical staff. At the final stage, the data of abdominal organs ultrasound examination were analyzed based on the materials of medical staff outpatient records. Results. The GSD prevalence among doctors was 33.3%, and 24.4% among nurses. In both groups age, AH, weight, WC and BMI contribute to GSD formation. In the first group of individuals with GSD, the level of total cholesterol (TC) was&nbsp;significantly higher. In the same group extremely high PB, postmenopause (p &lt;0.05) and hypodynamia (p &lt;0.1) were much more common. In the second group, there were more DM cases and pregnancies (p &lt;0.05). Conclusion. The medical staff of the clinic has a high GSD incidence, whose frequency depends not only on classical risk factors prevalence, but is also determined by profession peculiarities, characterized by high psychological stress and lower physical activity of physicians, compared to nurses.Цель исследования. Выявить факторы риска развития желчнокаменной болезни (ЖКБ) среди медицинского персонала поликлиники в разных профессиональных группах. Материалы и методы. В поликлинике было осмотрено и анкетировано 75 медицинских сотрудников поликлиники, которые были разделены на две группы. В 1-ю были включены 30 врачей; во 2-ю - 45 медицинских сестер. Анализу подвергались такие показатели, как профессия, пол, возраст, объем талии (ОТ), индекс массы тела (ИМТ), курение, наличие артериальной гипертензии (АГ), сахарного диабета (СД), гиперхолестеринемии, постменопаузы; у женщин – количество беременностей и прием оральных контрацептивов (ОК). Для оценки физической активности применяли краткий международный опросник по физической активности (IPAQ). Для выявления симптомов профессионального выгорания (ПВ) использовали опросник Maslach Burnout Inventory (MBI), адаптированный Н.Е. Водопьяновой для медицинских сотрудников. На конечном этапе анализировались данные ультразвукового исследования органов брюшной полости по амбулаторным картам медицинских&nbsp;работников. Результаты. Распространенность ЖКБ среди врачей составила 33,3%, и 24,4% среди медицинских сестер. В обеих группах на формирование ЖКБ влияют возраст, наличие АГ, вес, ОТ, ИМТ. В первой группе лиц с ЖКБ уровень общего холестерина был достоверно выше (ОХ). В этой же группе ПВ крайне высокой степени, постменопауза (p&lt;0,05) и гиподинамия (p&lt;0,1) встречались значительно чаще. В группе медицинских сестер с ЖКБ отмечалось преобладание лиц с СД и большее число беременностей (p&lt;0,05). Заключение. У медицинского персонала поликлиники имеет место высокая распространенность ЖКБ, частота которой зависит не только от распространенности классических факторов риска, но и определяется особенностями профессиональной деятельности, характеризующейся высокой психологической нагрузкой и более низкой физической активностью врачебного персонала, по сравнению с медицинскими сестрами

Exact Quantum Monte Carlo Process for the Statistics of Discrete Systems

We introduce an exact Monte Carlo approach to the statistics of discrete quantum systems which does not rely on the standard fragmentation of the imaginary time, or any small parameter. The method deals with discrete objects, kinks, representing virtual transitions at different moments of time. The global statistics of kinks is reproduced by explicit local procedures, the key one being based on the exact solution for the biased two-level system.Comment: 4 pages, latex, no figures, English translation of the paper

Dissipative dynamics of superfluid vortices at non-zero temperatures

We consider the evolution and dissipation of vortex rings in a condensate at non-zero temperature, in the context of the classical field approximation, based on the defocusing nonlinear Schr\"odinger equation. The temperature in such a system is fully determined by the total number density and the number density of the condensate. A vortex ring is introduced into a condensate in a state of thermal equilibrium, and interacts with non-condensed particles. These interactions lead to a gradual decrease in the vortex line density, until the vortex ring completely disappears. We show that the square of the vortex line length changes linearly with time, and obtain the corresponding universal decay law. We relate this to mutual friction coefficients in the fundamental equation of vortex motion in superfluids.Comment: 4 pages, 3 figure

Decay of quantised vorticity by sound emission

It is thought that in a quantum fluid sound generation is the ultimate sink of turbulent kinetic energy in the absence of any other dissipation mechanism near absolute zero. We show that a suitably trapped Bose-Einstein condensate provides a model system to study the sound emitted by accelerating vortices in a controlled way.Comment: 6 pages, 3 figure

Ultracold Dipolar Gases in Optical Lattices

This tutorial is a theoretical work, in which we study the physics of ultra-cold dipolar bosonic gases in optical lattices. Such gases consist of bosonic atoms or molecules that interact via dipolar forces, and that are cooled below the quantum degeneracy temperature, typically in the nK range. When such a degenerate quantum gas is loaded into an optical lattice produced by standing waves of laser light, new kinds of physical phenomena occur. These systems realize then extended Hubbard-type models, and can be brought to a strongly correlated regime. The physical properties of such gases, dominated by the long-range, anisotropic dipole-dipole interactions, are discussed using the mean-field approximations, and exact Quantum Monte Carlo techniques (the Worm algorithm).Comment: 56 pages, 26 figure