938 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
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
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.
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
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
Protocols for the assessment of building sustainability level. A new proposal for the Italian context
The paper aims at illustrating an innovative methodology for the development of a system to assess and rate the sustainability level of buildings, with particular reference to the Italian context. First, a review of the state of the art is presented, focusing on the existing sustainability tools, which characterize the building sector. Afterwards, the main criticalities of the current systems are pointed out, laying the basis for the setting-up of the new protocol. Consequently, the paper illustrates the process leading to the development of the new sustainability evaluation system, showing all the main steps towards its final inner structure. Finally, the research work introduces the concept of âbenchmarkâ, underlining its importance within the new protocol framework. In particular, the absence of reference or limit values for some performance indicators is emphasized and a computation methodology is proposed for those performance indicators lacking of benchmark values, with respect to the Italian background.
As a result, the paper provides an effective methodological and operative tool for decision makers, such as designers, constructors, developers and users of sustainability systems. The outcomes offer a contribution to the national and international development of methods and guidelines, supporting the overall sustainability evaluations in the building field
BUILDING PERFORMANCE SIMULATION PROGRAMS: BETWEEN âOPERABILITYâ AND âADEQUACYâ
Energy efficiency in Buildings, combined with an efficient use of the energy provided by renewable sources, are essential objectives set by the revision of the European Energy Performance of Buildings Directive. To achieve these objectives, an accurate estimate of the behavior of the system to be built/improved must be available during all stages of the design process or energy audit (if existing). While designing or improving energy efficiency, other important and associated goals must be ad-dressed, such as environmental health (hygrothermal, acoustic and luminous), costs, environmental sustainability, etc. Having to choose a dynamic simulation program to inform the design process it is necessary to analyze the possibilities offered by different available software, in terms of accuracy and completeness, while taking into account ease of use and included facilities aimed at supporting the design process itself. Over the past years, numerous Building Performance Simulation tools (BPSts) have been developed with the ambition of removing some shortages of existing BPSts in addressing todayâs usersâ requirements, sometimes by underestimating the reasons for those lacks of functionality. A software improvement that is focused only on usability might oversimplifies the complexity of the model used by the tool, or its use, while a focus on rapid prototyping might respond poorly to the requirements of a certain typology of users. A critical review of todayâs requirements and available tools is here presented, with the aim of informing a better awareness of possibilities offered or denied by current BPSts
Nonlinear quantum model for atomic Josephson junctions with one and two bosonic species
We study atomic Josephson junctions (AJJs) with one and two bosonic species
confined by a double-well potential. Proceeding from the second quantized
Hamiltonian, we show that it is possible to describe the zero-temperature AJJs
microscopic dynamics by means of extended Bose-Hubbard (EBH) models, which
include usually-neglected nonlinear terms. Within the mean-field approximation,
the Heisenberg equations derived from such two-mode models provide a
description of AJJs macroscopic dynamics in terms of ordinary differential
equations (ODEs). We discuss the possibility to distinguish the Rabi,
Josephson, and Fock regimes, in terms of the macroscopic parameters which
appear in the EBH Hamiltonians and, then, in the ODEs. We compare the
predictions for the relative populations of the Bose gases atoms in the two
wells obtained from the numerical solutions of the two-mode ODEs, with those
deriving from the direct numerical integration of the Gross-Pitaevskii
equations (GPEs). Our investigations shows that the nonlinear terms of the ODEs
are crucial to achieve a good agreement between ODEs and GPEs approaches, and
in particular to give quantitative predictions of the self-trapping regime.Comment: Accepted for the publication in J. Phys. B: At. Mol. Opt. Phy
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