On-site number statistics of ultracold lattice bosons

We study on-site occupation number fluctuations in a system of interacting bosons in an optical lattice. The ground-state distribution is obtained analytically in the limiting cases of strong and weak interaction, and by means of exact Monte Carlo simulations in the strongly correlated regime. As the interaction is increased, the distribution evolves from Poissonian in the non-interacting gas to a sharply peaked distribution in the Mott-insulator (MI) regime. In the special case of large occupation numbers, we demonstrate analytically and check numerically that there exists a wide interval of interaction strength, in which the on-site number fluctuations remain Gaussian and are gradually squeezed until they are of order unity near the superfluid (SF)-MI transition. Recently, the on-site number statistics were studied experimentally in a wide range of lattice potential depths [Phys. Rev. Lett. \textbf{96}, 090401 (2006)]. In our simulations, we are able to directly reproduce experimental conditions using temperature as the only free parameter. Pronounced temperature dependence suggests that measurements of on-site atom number fluctuations can be employed as a reliable method of thermometry in both SF and MI regimes.Comment: 9 pages, 4 figure

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

Differential approximation for Kelvin-wave turbulence

I present a nonlinear differential equation model (DAM) for the spectrum of Kelvin waves on a thin vortex filament. This model preserves the original scaling of the six-wave kinetic equation, its direct and inverse cascade solutions, as well as the thermodynamic equilibrium spectra. Further, I extend DAM to include the effect of sound radiation by Kelvin waves. I show that, because of the phonon radiation, the turbulence spectrum ends at a maximum frequency $\omega^* \sim (\epsilon^3 c_s^{20} / \kappa^{16})^{1/13}$ where $\epsilon$ is the total energy injection rate, $c_s$ is the speed of sound and $\kappa$ is the quantum of circulation.Comment: Prepared of publication in JETP Letter

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

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

Phase diagram of two-component bosons on an optical lattice

We present a theoretical analysis of the phase diagram of two--component bosons on an optical lattice. A new formalism is developed which treats the effective spin interactions in the Mott and superfluid phases on the same footing. Using the new approach we chart the phase boundaries of the broken spin symmetry states up to the Mott to superfluid transition and beyond. Near the transition point, the magnitude of spin exchange can be very large, which facilitates the experimental realization of spin-ordered states. We find that spin and quantum fluctuations have a dramatic effect on the transition making it first order in extended regions of the phase diagram. For Mott states with even occupation we find that the competition between effective Heisenberg exchange and spin-dependent on--site interaction leads to an additional phase transition from a Mott insulator with no broken symmetries into a spin-ordered insulator

The approach to vortex reconnection

We present numerical solutions of the Gross--Pitaevskii equation corresponding to reconnecting vortex lines. We determine the separation of vortices as a function of time during the approach to reconnection, and study the formation of pyramidal vortex structures. Results are compared with analytical work and numerical studies based on the vortex filament method.Comment: 11 pages, 9 figure

Identification of Kelvin waves: numerical challenges

Kelvin waves are expected to play an essential role in the energy dissipation for quantized vortices. However, the identification of these helical distortions is not straightforward, especially in case of vortex tangle. Here we review several numerical methods that have been used to identify Kelvin waves within the vortex filament model. We test their validity using several examples and estimate whether these methods are accurate enough to verify the correct Kelvin spectrum. We also illustrate how the correlation dimension is related to different Kelvin spectra and remind that the 3D energy spectrum E(k) takes the form 1/k in the high-k region, even in the presence of Kelvin waves.Comment: 6 pages, 5 figures. The final publication is available at http://www.springerlink.co

Influence of nearly resonant light on the scattering length in low-temperature atomic gases

We develop the idea of manipulating the scattering length $a$ in low-temperature atomic gases by using nearly resonant light. As found, if the incident light is close to resonance with one of the bound $p$ levels of electronically excited molecule, then virtual radiative transitions of a pair of interacting atoms to this level can significantly change the value and even reverse the sign of $a$. The decay of the gas due to photon recoil, resulting from the scattering of light by single atoms, and due to photoassociation can be minimized by selecting the frequency detuning and the Rabi frequency. Our calculations show the feasibility of optical manipulations of trapped Bose condensates through a light-induced change in the mean field interaction between atoms, which is illustrated for $^7$Li.Comment: 12 pages, 1 Postscript figur