758 research outputs found
Effective-range signatures in quasi-1D matter waves: sound velocity and solitons
We investigate ultracold and dilute bosonic atoms under strong transverse
harmonic confinement by using a 1D modified Gross-Pitaevskii equation (1D
MGPE), which accounts for the energy dependence of the two-body scattering
amplitude within an effective-range expansion. We study sound waves and
solitons of the quasi-1D system comparing 1D MGPE results with the 1D GPE ones.
We point out that, when the finite-size nature of the interaction is taken into
account, the speed of sound and the density profiles of both dark and bright
solitons show relevant quantitative changes with respect to what predicted by
the standard 1D GPE.Comment: 13 pages, 4 figures, improved version, added a figure and two
references, to be published in J. Phys. B: At. Mol. Opt. Phy
Extended Bose Hubbard model of interacting bosonic atoms in optical lattices: from superfluidity to density waves
For systems of interacting, ultracold spin-zero neutral bosonic atoms,
harmonically trapped and subject to an optical lattice potential, we derive an
Extended Bose Hubbard (EBH) model by developing a systematic expansion for the
Hamiltonian of the system in powers of the lattice parameters and of a scale
parameter, the {\it lattice attenuation factor}. We identify the dominant terms
that need to be retained in realistic experimental conditions, up to
nearest-neighbor interactions and nearest-neighbor hoppings conditioned by the
on site occupation numbers. In mean field approximation, we determine the free
energy of the system and study the phase diagram both at zero and at finite
temperature. At variance with the standard on site Bose Hubbard model, the zero
temperature phase diagram of the EBH model possesses a dual structure in the
Mott insulating regime. Namely, for specific ranges of the lattice parameters,
a density wave phase characterizes the system at integer fillings, with domains
of alternating mean occupation numbers that are the atomic counterparts of the
domains of staggered magnetizations in an antiferromagnetic phase. We show as
well that in the EBH model, a zero-temperature quantum phase transition to pair
superfluidity is in principle possible, but completely suppressed at lowest
order in the lattice attenuation factor. Finally, we determine the possible
occurrence of the different phases as a function of the experimentally
controllable lattice parameters.Comment: 18 pages, 7 figures, accepted for publication in Phys. Rev.
Brevi note in margine al caso Englaro: a proposito di interpretazione "giurisprudenziale" e di dimensione storico-sociale del diritto
La \uabEscuela social del derecho\ubb entre Europa y Brasil. Encuentros y desencuentros ante las transformaciones de fin de siglo.
Las proyecciones europeas y latinoamericanas de la \uabEscuela social del derecho\ubb, que floreci\uf3 en Italia en los \ufaltimos veinte a\uf1os del siglo XIX, ofrecen un escenario rico en contaminaciones, derivaciones y sugestiones, correspondencias y coincidencias, pero tambi\ue9n silencios e indiferencias. Los \uabneot\ue9ricos\ubb italianos lanzaron una piedra que agit\uf3 las aguas tranquilas del estanque legalista, produciendo una ola destinada a encontrarse con las tendencias an\ue1logas que estaban germinando en la crisis de fin de siglo a una y otra orilla del Atl\ue1ntico. Un encuentro obligado en el plano de las sugestiones, de los contenidos y del m\ue9todo, pero no siempre consumado, declarado y formalizado; un di\ue1logo tangible, parad\uf3jicamente, m\ue1s en la larga distancia que en la corta, m\ue1s con las j\uf3venes y lejanas escuelas de la Am\ue9rica Latina que con las s\uf3lidas y cercanas de la Europa continental
Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential
We study the exact dynamics of a one-dimensional spin-polarized gas of
fermions in a double-well potential at zero and finite temperature. Despite the
system is made of non-interacting fermions, its dynamics can be quite complex,
showing strongly aperiodic spatio-temporal patterns during the tunneling. The
extension of these results to the case of mixtures of spin-polarized fermions
in interaction with self-trapped Bose-Einstein condensates (BECs) at zero
temperature is considered as well. In this case we show that the fermionic
dynamics remains qualitatively similar to the one observed in absence of BEC
but with the Rabi frequencies of fermionic excited states explicitly depending
on the number of bosons and on the boson-fermion interaction strength. From
this, the possibility to control quantum fermionic dynamics by means of
Feshbach resonances is suggested.Comment: Accepted for publication in Phys. Rev.
Massive Quantum Memories by Periodically Inverted Dynamic Evolutions
We introduce a general scheme to realize perfect quantum state reconstruction
and storage in systems of interacting qubits. This novel approach is based on
the idea of controlling the residual interactions by suitable external controls
that, acting on the inter-qubit couplings, yield time-periodic inversions in
the dynamical evolution, thus cancelling exactly the effects of quantum state
diffusion. We illustrate the method for spin systems on closed rings with XY
residual interactions, showing that it enables the massive storage of
arbitrarily large numbers of local states, and we demonstrate its robustness
against several realistic sources of noise and imperfections.Comment: 10 pages, 3 figures. Contribution to the Proceedings of the Workshop
on "Quantum entanglement in physical and information sciences", held in Pisa,
December 14-18, 200
Rabi-Josephson oscillations and self-trapped dynamics in atomic junctions with two bosonic species
We investigate the dynamics of two-component Bose-Einstein condensates
(BECs), composed of atoms in two distinct hyperfine states, which are linearly
coupled by two-photon Raman transitions. The condensate is loaded into a
double-well potential (DWP). A variety of dynamical behaviors, ranging from
regular Josephson oscillations, to mixed Rabi-Josephson oscillations and to
regimes featuring an increasing complexity, are described in terms of a reduced
Hamiltonian system with four degrees of freedoms, which are the numbers of
atoms in each component in the left and right potential wells, whose
canonically conjugate variables are phases of the corresponding wave functions.
Using the system with the four degrees of freedom, we study the dynamics of
fractional imbalances of the two bosonic components, and compare the results to
direct simulations of the Gross-Pitaevskii equations (GPEs) describing the
bosonic mixture. We perform this analysis when the fractional imbalance
oscillates around a zero-time averaged value and in the self-trapping regime as
well.Comment: 18 pages, 7 figures, accepted for publication in J. Phys. B: At. Mol.
Opt. Phy
Influence of trapping potentials on the phase diagram of bosonic atoms in optical lattices
We study the effect of external trapping potentials on the phase diagram of
bosonic atoms in optical lattices. We introduce a generalized Bose-Hubbard
Hamiltonian that includes the structure of the energy levels of the trapping
potential, and show that these levels are in general populated both at finite
and zero temperature. We characterize the properties of the superfluid
transition for this situation and compare them with those of the standard
Bose-Hubbard description. We briefly discuss similar behaviors for fermionic
systems.Comment: 4 pages, 3 figures; final version, to be published in Phys. Rev.
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