2,464 research outputs found

    Finite temperature analysis of a quasi2D dipolar gas

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    We present finite temperature analysis of a quasi2D dipolar gas. To do this, we use the Hartree Fock Bogoliubov method within the Popov approximation. This formalism is a set of non-local equations containing the dipole-dipole interaction and the condensate and thermal correlation functions, which are solved self-consistently. We detail the numerical method used to implement the scheme. We present density profiles for a finite temperature dipolar gas in quasi2D, and compare these results to a gas with zero-range interactions. Additionally, we analyze the excitation spectrum and study the impact of the thermal exchange

    Excited states of a static dilute spherical Bose condensate in a trap

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    The Bogoliubov approximation is used to study the excited states of a dilute gas of NN atomic bosons trapped in an isotropic harmonic potential characterized by a frequency ω0\omega_0 and an oscillator length d0=/mω0d_0 = \sqrt{\hbar/m\omega_0}. The self-consistent static Bose condensate has macroscopic occupation number N01N_0 \gg 1, with nonuniform spherical condensate density n0(r)n_0(r); by assumption, the depletion of the condensate is small (NNN0N0N' \equiv N - N_0\ll N_0). The linearized density fluctuation operator ρ^\hat \rho' and velocity potential operator Φ^\hat\Phi' satisfy coupled equations that embody particle conservation and Bernoulli's theorem. For each angular momentum ll, introduction of quasiparticle operators yields coupled eigenvalue equations for the excited states; they can be expressed either in terms of Bogoliubov coherence amplitudes ul(r)u_l(r) and vl(r)v_l(r) that determine the appropriate linear combinations of particle operators, or in terms of hydrodynamic amplitudes ρl(r)\rho_l'(r) and Φl(r)\Phi_l'(r). The hydrodynamic picture suggests a simple variational approximation for l>0l >0 that provides an upper bound for the lowest eigenvalue ωl\omega_l and an estimate for the corresponding zero-temperature occupation number NlN_l'; both expressions closely resemble those for a uniform bulk Bose condensate.Comment: 5 pages, RevTeX, contributed paper accepted for Low Temperature Conference, LT21, August, 199

    Energy and Vorticity in Fast Rotating Bose-Einstein Condensates

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    We study a rapidly rotating Bose-Einstein condensate confined to a finite trap in the framework of two-dimensional Gross-Pitaevskii theory in the strong coupling (Thomas-Fermi) limit. Denoting the coupling parameter by 1/\eps^2 and the rotational velocity by Ω\Omega, we evaluate exactly the next to leading order contribution to the ground state energy in the parameter regime |\log\eps|\ll \Omega\ll 1/(\eps^2|\log\eps|) with \eps\to 0. While the TF energy includes only the contribution of the centrifugal forces the next order corresponds to a lattice of vortices whose density is proportional to the rotational velocity.Comment: 19 pages, LaTeX; typos corrected, clarifying remarks added, some rearrangements in the tex

    Thermodynamics of Solitonic Matter Waves in a Toroidal Trap

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    We investigate the thermodynamic properties of a Bose-Einstein condensate with negative scattering length confined in a toroidal trapping potential. By numerically solving the coupled Gross-Pitaevskii and Bogoliubov-de Gennes equations, we study the phase transition from the uniform state to the symmetry-breaking state characterized by a bright-soliton condensate and a localized thermal cloud. In the localized regime three states with a finite condensate fraction are present: the thermodynamically stable localized state, a metastable localized state and also a metastable uniform state. Remarkably, the presence of the stable localized state strongly increases the critical temperature of Bose-Einstein condensation.Comment: 4 pages, 4 figures, to be published in Physical Review A as a Rapid Communication. Related papers can be found at http://www.padova.infm.it/salasnich/tdqg.htm

    Spin-dependent Hedin's equations

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    Hedin's equations for the electron self-energy and the vertex were originally derived for a many-electron system with Coulomb interaction. In recent years it has been increasingly recognized that spin interactions can play a major role in determining physical properties of systems such as nanoscale magnets or of interfaces and surfaces. We derive a generalized set of Hedin's equations for quantum many-body systems containing spin interactions, e.g. spin-orbit and spin-spin interactions. The corresponding spin-dependent GW approximation is constructed.Comment: 5 pages, 1 figur

    A simple mean field equation for condensates in the BEC-BCS crossover regime

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    We present a mean field approach based on pairs of fermionic atoms to describe condensates in the BEC-BCS crossover regime. By introducing an effective potential, the mean field equation allows us to calculate the chemical potential, the equation of states and the atomic correlation function. The results agree surprisingly well with recent quantum Monte Carlo calculations. We show that the smooth crossover from the bosonic mean field repulsion between molecules to the Fermi pressure among atoms is associated with the evolution of the atomic correlation function

    Quantum Monte Carlo study of dilute neutron matter at finite temperatures

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    We report results of fully non-perturbative, Path Integral Monte Carlo (PIMC) calculations for dilute neutron matter. The neutron-neutron interaction in the s channel is parameterized by the scattering length and the effective range. We calculate the energy and the chemical potential as a function of temperature at the density \dens=0.003\fm^{-3}. The critical temperature \Tc for the superfluid-normal phase transition is estimated from the finite size scaling of the condensate fraction. At low temperatures we extract the spectral weight function A(p,ω)A(p,\omega) from the imaginary time propagator using the methods of maximum entropy and singular value decomposition. We determine the quasiparticle spectrum, which can be accurately parameterized by three parameters: an effective mass mm^*, a mean-field potential UU, and a gap Δ\Delta. Large value of \Delta/\Tc indicates that the system is not a BCS-type superfluid at low temperatures.Comment: 4 pages, 3 figure

    Thermodynamic properties of a dipolar Fermi gas

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    Based on the semi-classical theory, we investigate the thermodynamic properties of a dipolar Fermi gas. Through a self-consistent procedure, we numerically obtain the phase space distribution function at finite temperature. We show that the deformations in both momentum and real space becomes smaller and smaller as one increases the temperature. For homogeneous case, we also calculate pressure, entropy, and heat capacity. In particular, at low temperature limit and in weak interaction regime, we obtain an analytic expression for the entropy, which agrees qualitatively with our numerical result. The stability of a trapped gas at finite temperature is also explored

    Hartree shift in unitary Fermi gases

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    The Hartree energy shift is calculated for a unitary Fermi gas. By including the momentum dependence of the scattering amplitude explicitly, the Hartree energy shift remains finite even at unitarity. Extending the theory also for spin-imbalanced systems allows calculation of polaron properties. The results are in good agreement with more involved theories and experiments.Comment: 31 pages, many figure