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

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.

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

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.

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.

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 ‘benchmark’, 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