arXiv subjects

P. Pedri

Publications and source records attributed to P. Pedri.

29 records · Page 2Linked to original sources

arXiv2005

Two-dimensional bright solitons in dipolar Bose-Einstein condensates

We analyze the physics of bright solitons in two-dimensional dipolar Bose-Einstein condensates. These solitons are not possible in short-range interacting gases. In particular, we discuss the necessary conditions for the existence of stable 2D bright solitary waves. The stability of the solutions is studied by means of the analysis of lowest-lying excitations. Additionally, we study the scattering of solitary waves, which contrary to the contact-interacting case, is inelastic, and could lead to fusion of solitary waves. Finally, the experimental possibilities for observability are discussed.

cond-mat.other↗

arXiv2004

Mott-insulator phase of coupled 1D atomic gases in a 2D optical lattice

We discuss the 2D Mott insulator (MI) state of a 2D array of coupled finite size 1D Bose gases. It is shown that the momentum distribution in the lattice plane is very sensitive to the interaction regime in the 1D tubes. In particular, we find that the disappearance of the interference pattern in time of flight experiments will not be a signature of the MI phase, but a clear consequence of the strongly interacting Tonks-Girardeau regime along the tubes.

cond-mat.mes-hall↗

arXiv2004

Collisions and expansion of an ultracold dilute Fermi gas

We discuss the effects of collisions on the expansion of a degenerate normal Fermi gas, following the sudden removal of the confining trap. Using a Boltzmann equation approach, we calculate the time dependence of the aspect ratio and the entropy increase of the expanding atomic cloud taking into account the collisional effects due to the deformation of the distribution function in momentum space. We find that in dilute gases the aspect ratio does not deviate significantly from the predictions of ballistic expansion. Conversely, if the trap is sufficiently elongated the thermal broadening of the density distribution due to the entropy increase can be sizeable, revealing that even at zero temperature collisions are effective in a Fermi gas.

cond-mat.stat-mech↗

arXiv2003

Scissors modes of two-component degenerate gases: Bose-Bose and Bose-Fermi mixtures

We investigate the scissors modes in binary mixtures of degenerate dilute quantum gases, for both Bose-Bose and Bose-Fermi mixtures. For the latter we consider both the superfluid and normal hydrodynamic and collisionless regimes. We analyze the dependence of the frequencies of the scissors modes and their character as a function of the Bose-Fermi coupling and the trap geometry. We show that the scissors mode can reveal a clear trace of the hydrodynamic behavior of the Fermi gas.

cond-mat.soft↗

arXiv2003

Creation of discrete solitons and observation of the Peierls-Nabarro barrier in Bose-Einstein Condensates

We analyze the generation and mobility of discrete solitons in Bose-Einstein condensates confined in an optical lattice under realistic experimental conditions. We discuss first the creation of 1D discrete solitons, for both attractive and repulsive interatomic interactions. We then address the issue of their mobility, focusing our attention on the conditions for the experimental observability of the Peierls-Nabarro barrier. Finally we report on the generation of self-trapped structures in two and three dimensions. Discrete solitons may open alternative routes for the manipulation and transport of Bose-Einstein condensates.

cond-mat↗

arXiv2003

Three-dimensional quasi-Tonks gas in a harmonic trap

We analyze the macroscopic dynamics of a Bose gas in a harmonic trap with a superimposed two-dimensional optical lattice, assuming a weak coupling between different lattice sites. We consider the situation in which the local chemical potential at each lattice site can be considered as that provided by the Lieb-Liniger solution. Due to the weak coupling between sites and the form of the chemical potential, the three-dimensional ground-state density profile and the excitation spectrum acquire remarkable properties different from both 1D and 3D gases. We call this system a quasi-Tonks gas. We discuss the range of applicability of this regime, as well as realistic experimental situations where it can be observed.

cond-mat↗

arXiv2003

Dynamics of a classical gas including dissipative and mean field effects

By means of a scaling ansatz, we investigate an approximated solution of the Boltzmann-Vlasov equation for a classical gas. Within this framework, we derive the frequencies and the damping of the collective oscillations of a harmonically trapped gas and we investigate its expansion after release of the trap. The method is well suited to studying the collisional effects taking place in the system and in particular to discussing the crossover between the hydrodynamic and the collisionless regimes. An explicit link between the relaxation times relevant for the damping of the collective oscillations and for the expansion is established.

cond-mat↗

arXiv2003

Violation of self-similarity in the expansion of a 1D Bose gas

The expansion of a 1D Bose gas is investigated employing the Lieb-Liniger equation of state within the local density approximation. We show that during the expansion the density profile of the gas does not follow a self-similar solution, as one would expect from a simple scaling Ansatz. We carry out a variational calculation, which recovers the numerical results for the expansion, the equilibrium properties of the density profile, and the frequency of the lowest compressional mode. The variational approach allows for the analysis of the expansion in all interaction regimes between the mean field and the Tonks-Girardeau limits, and in particular shows the range of parameters for which the expansion violates self-similarity.

cond-mat↗

arXiv2002

Expansion of an interacting Fermi gas

We study the expansion of a dilute ultracold sample of fermions initially trapped in a anisotropic harmonic trap. The expansion of the cloud provides valuable information about the state of the system and the role of interactions. In particular the time evolution of the deformation of the expanding cloud behaves quite differently depending on whether the system is in the normal or in the superfluid phase. For the superfluid phase, we predict an inversion of the deformation of the sample, similarly to what happens with Bose-Einstein condensates. Viceversa, in the normal phase, the inversion of the aspect ratio is never achieved, if the mean field interaction is attractive and collisions are negligible.

cond-mat.soft↗

arXiv2001

Expansion of a coherent array of Bose-Einstein condensates

We investigate the properties of a coherent array containing about 200 Bose-Einstein condensates produced in a far detuned 1D optical lattice. The density profile of the gas, imaged after releasing the trap, provides information about the coherence of the ground-state wavefunction. The measured atomic distribution is characterized by interference peaks. The time evolution of the peaks, their relative population as well as the radial size of the expanding cloud are in good agreement with the predictions of theory. The 2D nature of the trapped condensates and the conditions required to observe the effects of coherence are also discussed.

cond-mat.soft↗

arXiv2001

Consequence of superfluidity on the expansion of a rotating Bose-Einstein condensate

We study the time evolution of a rotating condensate, that expands after being suddenly released from the confining trap, by solving the hydrodynamic equations of irrotational superfluids. For slow initial rotation speeds, $Ω_{0}$, we find that the condensate's angular velocity increases rapidly to a maximum value and this is accompanied by a minimum in the deformation of the condensate in the rotating plane. During the expansion the sample makes a global rotation of approximately $π/2$, where the exact value depends on $Ω_{0}$. This minimum deformation can serve as an easily detectable signature of superfluidity in a Bose--Einstein condensate.

cond-mat.soft↗