DSpace Collection:
http://hdl.handle.net/2445/19703
2019-02-19T16:54:48ZUnitary limit of two-nucleon interactions in strong magnetic fields
http://hdl.handle.net/2445/128472
Title: Unitary limit of two-nucleon interactions in strong magnetic fields
Author: Detmold, William; Orginos, Kostas; Parreño García, Assumpta; Savage, Martin J.; Tiburzi, Brian C.; Beane, Silas R.; Chang, Emmanuel
Abstract: Two-nucleon systems are shown to exhibit large scattering lengths in strong magnetic fields at unphysical quark masses, and the trends toward the physical values indicate that such features may exist in nature. Lattice QCD calculations of the energies of one and two nucleons systems are performed at pion masses of m π ∼ 450 and 806 MeV in uniform, time-independent magnetic fields of strength | B | ∼ 10 19 - 10 20 G to determine the response of these hadronic systems to large magnetic fields. Fields of this strength may exist inside magnetars and in peripheral relativistic heavy ion collisions, and the unitary behavior at large scattering lengths may have important consequences for these systems.2019-02-19T16:17:57ZTransport properties of the Fermi hard-sphere system
http://hdl.handle.net/2445/128470
Title: Transport properties of the Fermi hard-sphere system
Author: Mecca, Angela; Lovato, Alessandro; Benhar, Omar; Polls Martí, Artur
Abstract: The transport properties of neutron star matter play an important role in many astrophysical processes. We report the results of a calculation of the shear viscosity and thermal conductivity coefficients of the hard-sphere fermion system of degeneracy ν=2, that can be regarded as a model of pure neutron matter. Our approach is based on the effective interaction obtained from the formalism of correlated basis functions and the cluster expansion technique. The resulting transport coefficients show a strong sensitivity to the quasiparticle effective mass, reflecting the effect of second-order contributions to the self-energy that are not taken into account in nuclear matter studies available in the literature.2019-02-19T16:08:14ZShortcut to adiabaticity in spinor condensates
http://hdl.handle.net/2445/128469
Title: Shortcut to adiabaticity in spinor condensates
Author: Sala, Arnau; López Núñez, David; Martorell Domenech, Juan; Sarlo, Luigi De; Zibold, Tilman; Gerbier, Fabrice; Julia-Diaz, B.; Polls Martí, Artur
Abstract: We devise a method to shortcut the adiabatic evolution of a spin-1 Bose gas with an external magnetic field as the control parameter. An initial many-body state with almost all bosons populating the Zeeman sublevel m = 0 is evolved to a final state very close to a macroscopic spin-singlet condensate, a fragmented state with three macroscopically occupied Zeeman states. The shortcut protocol, obtained by an approximate mapping to a harmonic oscillator Hamiltonian, is compared to linear and exponential variations of the control parameter. We find a dramatic speedup of the dynamics when using the shortcut protocol.2019-02-19T15:44:59ZRole of correlations in spin-polarized neutron matter
http://hdl.handle.net/2445/128466
Title: Role of correlations in spin-polarized neutron matter
Author: Vidaña, Isaac; Polls Martí, Artur; Durant, Victoria
Abstract: Background: The possible existence of a phase transition to a ferromagnetic state in neutron matter as origin of the extremely high magnetic fields of neutron stars is still an open issue. Whereas many phenomenological interactions predict this transition at densities accessible in neutron stars, microscopic calculations based on realistic interactions show no indication of it. The existence or non-existence of this transition is a consequence of the different role of nucleon-nucleon correlations in polarized and unpolarized neutron matter. Therefore, to give a definite answer to this issue it is necessary to analyze the behavior of these correlations. Purpose: Using the Hellmann-Feynman theorem we analyze the contribution of the different terms of the nucleon-nucleon interaction to the spin symmetry energy of neutron matter with the purpose of identifying the nature and role of correlations in polarized and unpolarized neutron matter. Methods: The analysis is performed within the microscopic Brueckner-Hartree-Fock approach using the Argonne V18 realistic potential plus the Urbana IX three-body force. Results: Our results show no indication of a ferromagnetic transition as the spin symmetry energy of neutron matter is always an increasing function of density. They show also that the main contribution to it comes from the S = 0 channel, acting only in non-polarized neutron matter, in particular from the S-1(0) and the D-1(2) partial waves. Three-body forces are found to play a secondary role in the determination of the spin symmetry energy. Conclusions: By evaluating the kinetic energy difference between the correlated system and the underlying Fermi sea to estimate the importance of correlations in spin-polarized neutron matter, we conclude that non-polarized neutron matter is more correlated than totally polarized one.2019-02-19T12:51:04ZQuantum properties of a binary bosonic mixture in a double well
http://hdl.handle.net/2445/128464
Title: Quantum properties of a binary bosonic mixture in a double well
Author: Mujal Torreblanca, Pere; Juliá-Díaz, Bruno; Polls Martí, Artur
Abstract: This work contains a detailed analysis of the properties of the ground state of a two-component two-site Bose-Hubbard model, which captures the physics of a binary mixture of Bose-Einstein condensates trapped in a double-well potential. The atom-atom interactions within each species and among the two species are taken as variable parameters, while the hopping terms are kept fixed. To characterize the ground state, we use observables such as the imbalance of population and its quantum uncertainty. The quantum many-body correlations present in the system are further quantified by studying the degree of condensation of each species, the entanglement between the two sites, and the entanglement between the two species. The latter is measured by means of the Schmidt gap, the von Neumann entropy, or the purity obtained after tracing out a part of the system. A number of relevant states are identified, e.g., Schrödinger catlike many-body states, in which the outcome of the population imbalance of both components is completely correlated, and other states with even larger von Neumann entropy which have a large spread in Fock space.2019-02-19T12:38:22ZQuantum annealing for the number-partitioning problem using a tunable spin glass of ions
http://hdl.handle.net/2445/128316
Title: Quantum annealing for the number-partitioning problem using a tunable spin glass of ions
Author: Graß, Tobias; Raventós, David; Juliá-Díaz, Bruno; Gogolin, Christian; Lewenstein, Maciej
Abstract: Exploiting quantum properties to outperform classical ways of information processing is an outstanding goal of modern physics. A promising route is quantum simulation, which aims at implementing relevant and computationally hard problems in controllable quantum systems. Here we demonstrate that in a trapped ion setup, with present day technology, it is possible to realize a spin model of the Mattis-type that exhibits spin glass phases. Our method produces the glassy behaviour without the need for any disorder potential, just by controlling the detuning of the spin-phonon coupling. Applying a transverse field, the system can be used to benchmark quantum annealing strategies which aim at reaching the ground state of the spin glass starting from the paramagnetic phase. In the vicinity of a phonon resonance, the problem maps onto number partitioning, and instances which are difficult to address classically can be implemented.2019-02-15T12:45:36ZPairing in high-density neutron matter including short- and long-range correlations
http://hdl.handle.net/2445/128311
Title: Pairing in high-density neutron matter including short- and long-range correlations
Author: Ding, D.; Rios, A.; Dussan, H.; Dickhoff, W. H.; Carbone, A.; Polls Martí, Artur; Witte, S. J.
Abstract: Pairing gaps in neutron matter need to be computed in a wide range of densities to address open questions in neutron-star phenomenology. Traditionally, the Bardeen-Cooper-Schrieffer approach has been used to compute gaps from bare nucleon-nucleon interactions. Here we incorporate the influence of short-and long-range correlations in the pairing gaps. Short-range correlations are treated, including the appropriate fragmentation of single-particle states, and substantially suppress the gaps. Long-range correlations dress the pairing interaction via density and spin modes and provide a relatively small correction. We use different interactions, some with three-body forces, as a starting point to control for any systematic effects. Results are relevant for neutron-star cooling scenarios, in particular in view of the recent observational data on Cassiopeia A.2019-02-15T12:00:58ZModel dependence of the neutron-skin thickness on the symmetry energy
http://hdl.handle.net/2445/128277
Title: Model dependence of the neutron-skin thickness on the symmetry energy
Author: Mondal, C.; Agrawal, B. K.; Centelles Aixalà, Mario; Colò, G.; Roca-Maza, X.; Paar, N.; Viñas Gausí, Xavier; Singh, S. K.; Patra, S. K.
Abstract: The model dependence in the correlations of the neutron-skin thickness in heavy nuclei with various symmetry-energy parameters is analyzed by using several families of systematically varied microscopic mean-field models. Such correlations show a varying degree of model dependence once the results for all the different families are combined. Some mean-field models associated with similar values of the symmetry-energy slope parameter at saturation density L , and pertaining to different families, yield a greater-than-expected spread in the neutron-skin thickness of the 208 Pb nucleus. The effective value of the symmetry-energy slope parameter L eff , determined by using the nucleon density profiles of the finite nucleus and the density derivative S ′ ( ρ ) of the symmetry energy starting from about saturation density up to low densities typical of the surface of nuclei, seems to account for the spread in the neutron-skin thickness for the models with similar L . The differences in the values of L eff are mainly due to the small differences in the nucleon density distributions of heavy nuclei in the surface region and the behavior of the symmetry energy at subsaturation densities.2019-02-14T16:31:22ZMatter-wave recombiners fro trapped Bose-Einstein condensates
http://hdl.handle.net/2445/128273
Title: Matter-wave recombiners fro trapped Bose-Einstein condensates
Author: Berrada, T.; van Frank, S.; Bücker, R.; Schumm, T.; Schaff, J. F.; Schmiedmayer, J.; Juliá-Díaz, Bruno; Polls Martí, Artur
Abstract: Interferometry with trapped atomic Bose-Einstein condensates (BECs) requires the development of techniques to recombine the two paths of the interferometer and map the accumulated phase difference to a measurable atom number difference. We have implemented and compared two recombining procedures in a double-well-based BEC interferometer. The first procedure utilizes the bosonic Josephson effect and controlled tunneling of atoms through the potential barrier, similar to laser light in an optical fiber coupler. The second one relies on the interference of the reflected and transmitted parts of the BEC wave function when impinging on the potential barrier, analogous to light impinging on a half-silvered mirror. Both schemes were implemented successfully, yielding an interferometric contrast of similar to 20% and 42% respectively. Building efficient matter-wave recombiners represents an important step towards the coherent manipulation of external quantum superposition states of BECs.2019-02-14T16:00:19ZA Herschel/PACS Far-infrared line emission survey of local luminous infrared galaxies
http://hdl.handle.net/2445/128269
Title: A Herschel/PACS Far-infrared line emission survey of local luminous infrared galaxies
Author: Díaz-Santos, T.; Armus, L.; Charmandaris, V.; Lu, N.; Stierwalt, S.; Stacey, G.; Malhotra, S.; Werf, P.P.V.D.; Howell,J.H.; Privon, G.C.; Mazzarella, J.M.; Goldsmith, P.F.; Murphy, E.J.; Barcos-Muñoz, L.; Linden, S.T.; Inami, H.; Larson, K.L.; Evans, A.S.; Appleton, P.; Iwasawa, Kazushi; Lord, S.; Sanders, D.B.; Surace,J.A.
Abstract: We present an analysis of [OI]63, [OIII]88, [NII]122 and [CII]158 far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for ~240 local luminous infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey (GOALS). We find pronounced declines -deficits- of line-to-FIR-continuum emission for [NII]122, [OI]63 and [CII]158 as a function of FIR color and infrared luminosity surface density, $\Sigma_{\rm IR}$. The median electron density of the ionized gas in LIRGs, based on the [NII]122/[NII]205 ratio, is $n_{\rm e}$ = 41 cm$^{-3}$. We find that the dispersion in the [CII]158 deficit of LIRGs is attributed to a varying fractional contribution of photo-dissociation-regions (PDRs) to the observed [CII]158 emission, f([CII]PDR) = [CII]PDR/[CII], which increases from ~60% to ~95% in the warmest LIRGs. The [OI]63/[CII]158PDR ratio is tightly correlated with the PDR gas kinetic temperature in sources where [OI]63 is not optically-thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, $n_{\rm H}$, and intensity of the interstellar radiation field, in units of G$_0$, and find G$_0$/$n_{\rm H}$ ratios ~0.1-50 cm$^3$, with ULIRGs populating the upper end of the distribution. There is a relation between G$_0$/$n_{\rm H}$ and $\Sigma_{\rm IR}$, showing a critical break at $\Sigma_{\rm IR}^{\star}$ ~ 5 x 10$^{10}$ Lsun/kpc$^2$. Below $\Sigma_{\rm IR}^{\star}$, G$_0$/$n_{\rm H}$ remains constant, ~0.32 cm$^3$, and variations in $\Sigma_{\rm IR}$ are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above $\Sigma_{\rm IR}^{\star}$, G$_0$/$n_{\rm H}$ increases rapidly with $\Sigma_{\rm IR}$, signaling a departure from the typical PDR conditions found in normal star-forming galaxies towards more intense/harder radiation fields and compact geometries typical of starbursting sources.2019-02-14T15:15:42Z