1,358 research outputs found
Two-mode dipolar bosonic junctions
We consider a two-mode atomic Josephson junction realized with dilute dipolar
bosons confined by a double-well. We employ the two-site extended Bose-Hubbard
Hamiltonian and characterize the ground-state of this system by the Fisher
information, coherence visibility, and entanglement entropy. These quantities
are studied as functions of the interaction between bosons in different wells.
The emergence of Schroedinger-cat like state with a loss of coherence is also
commented.Comment: 9 pages, 1 figur
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
Quantum dynamics of a binary mixture of BECs in a double well potential: an Holstein-Primakoff approach
We study the quantum dynamics of a binary mixture of Bose-Einstein
condensates (BEC) in a double-well potential starting from a two-mode
Bose-Hubbard Hamiltonian. Focussing on the regime where the number of atoms is
very large, a mapping onto a SU(2) spin problem together with a
Holstein-Primakoff transformation is performed. The quantum evolution of the
number difference of bosons between the two wells is investigated for different
initial conditions, which range from the case of a small imbalance between the
two wells to a coherent spin state. The results show an instability towards a
phase-separation above a critical positive value of the interspecies
interaction while the system evolves towards a coherent tunneling regime for
negative interspecies interactions. A comparison with a semiclassical approach
is discussed together with some implications on the experimental realization of
phase separation with cold atoms.Comment: 12 pages, 7 figures, accepted for publication in J. Phys.
Pair condensation of polarized fermions in the BCS-BEC crossover
We investigate a two-component Fermi gas with unequal spin populations along
the BCS-BEC crossover. By using the extended BCS equations and the concept of
off-diagonal-long-range-order we derive a formula for the condensate number of
Cooper pairs as a function of energy gap, average chemical potential, imbalance
chemical potential and temperature. Then we study the zero-temperature
condensate fraction of Cooper pairs by varying interaction strength and
polarization, finding a depletion of the condensate fraction by increasing the
population imbalance. We also consider explicitly the presence of an external
harmonic confinement and we study, within the local-density approximation, the
phase separation between superfluid and normal phase regions of the polarized
fermionic cloud. In particular, we calculate both condensate density profiles
and total density profiles from the inner superfluid core to the normal region
passing for the interface, where a finite jump in the density is a clear
manifestation of this phase-separated regime. Finally, we compare our
theoretical results with the available experimental data on the condensate
fraction of polarized 6Li atoms [Science 311, 492 (2006)]. These experimental
data are in reasonable agreement with our predictions in a suitable range of
polarizations, but only in the BCS side of the crossover up to unitarity.Comment: 13 pages, 3 figures, improved version, added a section on the
interpretation of the results, to be published in J. Phys.
Quantum Bose Josephson Junction with binary mixtures of BECs
We study the quantum behaviour of a binary mixture of Bose-Einstein
condensates (BEC) in a double-well potential starting from a two-mode
Bose-Hubbard Hamiltonian. We focus on the small tunneling amplitude regime and
apply perturbation theory up to second order. Analytical expressions for the
energy eigenvalues and eigenstates are obtained. Then the quantum evolution of
the number difference of bosons between the two potential wells is fully
investigated for two different initial conditions: completely localized states
and coherent spin states. In the first case both the short and the long time
dynamics is studied and a rich behaviour is found, ranging from small amplitude
oscillations and collapses and revivals to coherent tunneling. In the second
case the short-time scale evolution of number difference is determined and a
more irregular dynamics is evidenced. Finally, the formation of Schroedinger
cat states is considered and shown to affect the momentum distribution.Comment: 14 pages, 4 figure
Photon-induced Self Trapping and Entanglement of a Bosonic Josephson Junction Inside an Optical Resonator
We study the influence of photons on the dynamics and the ground state of the
atoms in a Bosonic Josephson junction inside an optical resonator. The system
is engineered in such a way that the atomic tunneling can be tuned by changing
the number of photons in the cavity. In this setup the cavity photons are a new
means of control, which can be utilized both in inducing self-trapping
solutions and in driving the crossover of the ground state from an atomic
coherent state to a Schr\"odinger's cat state. This is achieved, for suitable
setup configurations, with interatomic interactions weaker than those required
in the absence of cavity. This is corroborated by the study of the entanglement
entropy. In the presence of a laser, this quantum indicator attains its maximum
value (which marks the formation of the cat-like state and, at a semiclassical
level, the onset of self-trapping) for attractions smaller than those of the
bare junction.Comment: 5 page
Computation of the Modes of Elliptic Waveguides with a Curvilinear 2D Frequency-Domain Finite-Difference Approach
A scalar Frequency-Domain Finite-Difference approach to the mode computation of elliptic waveguides is presented. The use of an elliptic cylindrical grid allows us to take exactly into account the curved boundary of the structure and a single mesh has been used both for TE and TM modes. As a consequence, a high accuracy is obtained with a reduced computational burden, since the resulting matrix is highly sparse
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.
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.
Entanglement entropy and macroscopic quantum states with dipolar bosons in a triple-well potential
We study interacting dipolar atomic bosons in a triple-well potential within
a ring geometry. This system is shown to be equivalent to a three-site
Bose-Hubbard model. We analyze the ground state of dipolar bosons by varying
the effective on-site interaction. This analysis is performed both numerically
and analytically by using suitable coherent-state representations of the ground
state. The latter exhibits a variety of forms ranging from the su(3) coherent
state in the delocalization regime to a macroscopic cat-like state with fully
localized populations, passing for a coexistence regime where the ground state
displays a mixed character. We characterize the quantum correlations of the
ground state from the bi-partition perspective. We calculate both numerically
and analytically (within the previous coherent-state representation) the
single-site entanglement entropy which, among various interesting properties,
exhibits a maximum value in correspondence to the transition from the cat-like
to the coexistence regime. In the latter case, we show that the ground-state
mixed form corresponds, semiclassically, to an energy exhibiting two
almost-degenerate minima.Comment: 9 pages, 2 figure
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