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L. Salasnich

Publications and source records attributed to L. Salasnich.

At least 127 records · Page 7Linked to original sources
arXiv2000

Thermodynamics of Bose-Condensed Atomic Hydrogen

We study the thermodynamics of the Bose-condensed atomic hydrogen confined in the Ioffe-Pritchard potential. Such a trapping potential, that models the magnetic trap used in recent experiments with hydrogen, is anharmonic and strongly anisotropic. We calculate the ground-state properties, the condensed and non-condensed fraction and the Bose-Einstein transition temperature. The thermodynamics of the system is strongly affected by the anharmonicity of this external trap. Finally, we consider the possibility to detect Josephson-like currents by creating a double-well barrier with a laser beam.

cond-mat.stat-mech↗
arXiv1999

Thermodynamics of a trapped Bose condensate with negative scattering length

We study the Bose-Einstein condensation (BEC) for a system of $^7Li$ atoms, which have negative scattering length (attractive interaction), confined in a harmonic potential. Within the Bogoliubov and Popov approximations, we numerically calculate the density profile for both condensate and non-condensate fractions and the spectrum of elementary excitations. In particular, we analyze the temperature and number-of-boson dependence of these quantities and evaluate the BEC transition temperature $T_{BEC}$. We calculate the loss rate for inelastic two- and three-body collisions. We find that the total loss rate is strongly dependent on the density profile of the condensate, but this density profile does not appreciably change by increasing the thermal fraction. Moreover, we study, using the quasi-classical Popov approximation, the temperature dependence of the critical number $N_c$ of condensed bosons, for which there is the collapse of the condensate. There are different regimes as a function of the total number $N$ of atoms. For $N N_c$ the condensate is metastable only for temperatures that exceed a critical value $T_c$.

cond-mat↗
arXiv1999

Bose Condensate in a Double-Well Trap: Ground State and Elementary Excitations

We study the Bose-Einstein condensate in the MIT double-well trap. We calculate the ground state density profile of $^{23}$Na atoms and the Bogoliubov spectrum of the elementary excitations as function of the strength of the double-well barrier. In particular, we analyze the behavior of quantum-mechanical collective excitations. Finally, we discuss the observability criteria for macroscopic quantum tunneling and macroscopic quantum self-trapping.

cond-mat.stat-mech↗
arXiv1999

Different Facets of Chaos in Quantum Mechanics

Nowadays there is no universally accepted definition of quantum chaos. In this paper we review and critically discuss different approaches to the subject, such as Quantum Chaology and the Random Matrix Theory. Then we analyze the problem of dynamical chaos and the time scales associated with chaos suppression in quantum mechanics. Summary: 1. Introduction 2. Quantum Chaology and Spectral Statistics 3. From Poisson to GOE Transition: Comparison with Experimental Data 3.1 Atomic Nuclei 3.2 The Hydrogen Atom in the Strong Magnetic Field 4. Quantum Chaos and Field Theory 5. Alternative Approaches to Quantum Chaos 6. Dynamical Quantum Chaos and Time Scales 6.1 Mean-Field Approximation and Dynamical Chaos 7. Conclusions

chao-dyn↗
arXiv1999

Bosons in a Toroidal Trap: Ground State and Vortices

We study the Bose-Einstein condensate (BEC) in a 3-D toroidal Mexican hat trap. By changing the parameters of the potential, or the number of bosons, it is possible to modify strongly the density profile of the BEC. We consider the ground state properties for positive and negative scattering length and calculate the spectrum elementary excitations. We also discuss the macroscopic phase coherence and superfluidity of the BEC by analyzing vortex states and their stability.

cond-mat↗
arXiv1998

Mean--Field and Nonlinear Dynamics in Many--Body Quantum Systems

In this paper we discuss in detail the nonlinear equations of the mean--field approximation and their connection to the exact many--body Schrödinger equation. Then we analyze the mean--field approach and the nonlinear dynamics of a trapped condensate of weakly--interacting bosons.

nucl-th↗
arXiv1998

Oscillation Frequencies for a Bose Condensate in a Triaxial Magnetic Trap

We investigate the dynamics of a Bose condensate, interacting with either repulsive or attractive forces, confined in a fully anisotropic harmonic potential. The (3+1)-dimensional Gross-Pitaevskii equation is integrated numerically to derive the collective excitation frequencies, showing a good agreement with those calculated with a variational technique.

cond-mat↗
arXiv1998

Bosonic clouds with attractive interaction beyond the local interaction approximation

We study the properties of a Bose-Einstein condensed cloud of atoms with negative scattering length confined in a harmonic trap. When a realistic non local (finite range) effective interaction is taken into account, we find that, besides the known low density metastable solution, a new branch of Bose condensate appears at higher density. This state is self-bound but its density can be quite low if the number $N$ of atoms is not too big. The transition between the two classes of solutions as a function of $N$ can be either sharp or smooth according to the ratio between the range of the attractive interaction and the length of the trap. A tight trap leads to a smooth transition. In addition to the energy and the shape of the cloud we study also the dynamics of the system. In particular, we study the frequencies of collective oscillation of the Bose condensate as a function of the number of atoms both in the local and in the non local case. Moreover, we consider the dynamics of the cloud when the external trap is switched off.

cond-mat↗
arXiv1998

Large Shell Model Calculations for Calcium Isotopes: Spectral Statistics and Chaos

We perform large shell model calculations for Calcium isotopes in the full fp shell by using the realistic Kuo-Brown interaction. The Calcium isotopes are especially interesting because the nearest-neighbour spacing distribution P(s) of low-lying energy levels shows significant deviations from the predictions of the Gaussian Orthogonal Ensemble of random--matrix theory. This contrasts with other neighbouring nuclei which show fully chaotic spectral distributions. We study the chaotic behaviour as a function of the excitation energy. In addition, a clear signature of chaos suppression is obtained when the single-particle spacings are increased. In our opinion the relatively weak strength of the neutron-neutron interaction is unable to destroy the regular single-particle mean-field motion completely. In the neighbouring nuclei with both protons and neutrons in valence orbits, on the other hand, the stronger proton-neutron interaction would appear to be sufficient to destroy the regular mean-field motion.

nucl-th↗
arXiv1997

New Results on Quantum Chaos in Atomic Nuclei

In atomic nuclei, ordered and chaotic states generally coexist. In this paper the transition from ordered to chaotic states will be discussed in the framework of roto-vibrational and shell models. In particular for $^{160}Gd$, in the roto-vibrational model, the Poincarè sections clearly show the transition from order to chaos for different values of rotational frequency. Furthermore, the spectral statistics of low-lying states of several $fp$ shell nuclei are studied with realistic shell-model calculations.

nucl-th↗
arXiv1997

Coexistence of Ordered and Chaotic States in Nuclear Structure

In atomic nuclei, as in other many-body systems, the classical phase space is mixed, so ordered and chaotic states generally coexist. In this contribution we discuss some models, showing the transition from order to chaos. In several cases a clear correspondence between classical and quantum chaos has been established. In particular the transition from ordered to chaotic states will be discussed in the framework of the shell and roto-vibrational models.

nucl-th↗
arXiv1997

Spectral Distribution Studies of fp shell nuclei with modified Kuo--Brown Interaction

The structure of nuclei in the lower half of fp shell is investigated by the spectral distribution method using the modified Kuo-Brown interaction. This interaction recently showed success in reproducing observed properties through detailed shell model studies. Spectral distribution studies avoid explicit diagonalization and hold promise for applications to astrophysics.

nucl-th↗
arXiv1995

Quantum Chaos in A=46--50 Atomic Nuclei

The spectral statistics of low--lying states of several $fp$ shell nuclei are studied with realistic shell--model calculations. For Ca isotopes, we find significant deviations from the predictions of the random--matrix theory which suggest that some spherical nuclei are not as chaotic in nature as the conventional view assumes.

nucl-th↗
arXiv1995

Quantum Corrections to the Semiclassical Quantization of the SU(3) Shell Model

We apply the canonical perturbation theory to the semi--quantal hamiltonian of the SU(3) shell model. Then, we use the Einstein--Brillowin--Keller quantization rule to obtain an analytical semi--quantal formula for the energy levels, which is the usual semi--classical one plus quantum corrections. Finally, a test on the numerical accuracy of the semiclassical approximation and of its quantum corrections is performed.

hep-th↗
arXiv1995

Spectral Statistics in Large Shell Model Calculations

The spectral statistics of low--lying states of $fp$ shell nuclei are studied by performing large shell--model calculations with a realistic nuclear interaction. For $Ca$ isotopes, we find deviations from the predictions of the random--matrix theory which suggest that some spherical nuclei are not as chaotic in nature as the conventional view assumes.

nucl-th↗