5,359 research outputs found
Size and shape of Mott regions for fermionic atoms in a two-dimensional optical lattice
We investigate the harmonic-trap control of size and shape of Mott regions in
the Fermi Hubbard model on a square optical lattice. The use of Lanczos
diagonalization on clusters with twisted boundary conditions, followed by an
average over 50-80 samples, drastically reduce finite-size effects in some
ground state properties; calculations in the grand canonical ensemble together
with a local-density approximation (LDA) allow us to simulate the radial
density distribution. We have found that as the trap closes, the atomic cloud
goes from a metallic state, to a Mott core, and to a Mott ring; the coverage of
Mott atoms reaches a maximum at the core-ring transition. A `phase diagram' in
terms of an effective density and the on-site repulsion is proposed, as a guide
to maximize the Mott coverage. We also predict that the usual experimentally
accessible quantities, the global compressibility and the average double
occupancy (rather, its density derivative) display detectable signatures of the
core-ring transition. Some spin correlation functions are also calculated, and
predict the existence N\'eel ordering within Mott cores and rings.Comment: 5 pages, 6 figure
Measuring von Neumann entanglement entropies without wave functions
We present a method to measure the von Neumann entanglement entropy of ground
states of quantum many-body systems which does not require access to the system
wave function. The technique is based on a direct thermodynamic study of
entanglement Hamiltonians, whose functional form is available from field
theoretical insights. The method is applicable to classical simulations such as
quantum Monte Carlo methods, and to experiments that allow for thermodynamic
measurements such as the density of states, accessible via quantum quenches. We
benchmark our technique on critical quantum spin chains, and apply it to
several two-dimensional quantum magnets, where we are able to unambiguously
determine the onset of area law in the entanglement entropy, the number of
Goldstone bosons, and to check a recent conjecture on geometric entanglement
contribution at critical points described by strongly coupled field theories
Impurities near an Antiferromagnetic-Singlet Quantum Critical Point
Heavy fermion systems, and other strongly correlated electron materials,
often exhibit a competition between antiferromagnetic (AF) and singlet ground
states. Using exact Quantum Monte Carlo (QMC) simulations, we examine the
effect of impurities in the vicinity of such AF- singlet quantum critical
points, through an appropriately defined impurity susceptibility, .
Our key finding is a connection, within a single calculational framework,
between AF domains induced on the singlet side of the transition, and the
behavior of the nuclear magnetic resonance (NMR) relaxation rate . We
show that local NMR measurements provide a diagnostic for the location of the
QCP which agrees remarkably well with the vanishing of the AF order parameter
and large values of . We connect our results with experiments on
Cd-doped CeCoIn
O pequeno agricultor e o uso de Tecnologias da Informação.
A elaboração deste resumo contou com leituras dos relatórios de três painéis de especialistas1 realizados em 2008, de artigo escrito por Oliveira et al. (2009), de notÃcias e reportagens encontradas em sÃtios online, além de números do banco de dados do projeto SW Agro - Estudo do Mercado Brasileiro de Software para o Agronegócio - realizado na Embrapa Informática Agropecuária referentes à s Empresas de Assistência Técnica e Extensão Rural (Ematers) e cooperativas. Mostra-se, portanto, que o acesso a esses documentos proporcionam interessantes análises
Engineering entanglement Hamiltonians with strongly interacting cold atoms in optical traps
We present a proposal for the realization of entanglement Hamiltonians in
one-dimensional critical spin systems with strongly interacting cold atoms. Our
approach is based on the notion that the entanglement spectrum of such systems
can be realized with a physical Hamiltonian containing a set of
position-dependent couplings. We focus on reproducing the universal ratios of
the entanglement spectrum for systems in two different geometries: a harmonic
trap, which corresponds to a partition embedded in an infinite system, and a
linear potential, which reproduces the properties of a half-partition with open
boundary conditions. Our results demonstrate the possibility of measuring the
entanglement spectra of the Heisenberg and XX models in a realistic cold-atom
experimental setting by simply using gravity and standard trapping techniques.Comment: 11 pages, 6 figure
Influence of preparation procedures on the phenolic content, antioxidant and antidiabetic activities of green and black teas
The influence of common tea preparation procedures (temperature, infusion time, consumption time interval and tea bag/loose-leaf) and the type of water used, on the total phenolic content (TPC), the radical scavenging activity and the alpha-glucosidase inhibitory activity were assessed. Higher TPC and antioxidant activity were obtained when using lower mineralized waters. Tea bags also evidenced higher antioxidant activity than loose-leaf samples. Under the same conditions (90 degrees C and five minutes of infusion time) green tea contains almost twice the quantity of polyphenols and the free radical scavenging ability of black tea. In the alpha-glucosidase assay all infusions were active (97-100 %). Furthermore, HPLC allowed to identify some of the polyphenols present in both teas and to monitor their composition change with time. After twenty-four hours, the antioxidant activity was maintained without significant changes, but a small decrease in enzyme inhibition was observed, although this activity was still very high.info:eu-repo/semantics/publishedVersio
Coherence Temperature in the Diluted Periodic Anderson Model
The Kondo and Periodic Anderson Model (PAM) are known to provide a
microscopic picture of many of the fundamental properties of heavy fermion
materials and, more generally, a variety of strong correlation phenomena in
and systems. In this paper, we apply the Determinant Quantum Monte
Carlo (DQMC) method to include disorder in the PAM, specifically the removal of
a fraction of the localized orbitals. We determine the evolution of the
coherence temperature , where the local moments and conduction electrons
become entwined in a heavy fermion fluid, with and with the hybridization
between localized and conduction orbitals. We recover several of the
principal observed trends in of doped heavy fermions, and also show that,
within this theoretical framework, the calculated Nuclear Magnetic Resonance
(NMR) relaxation rate tracks the experimentally measured behavior in pure and
doped CeCoIn. Our results contribute to important issues in the
interpretation of local probes of disordered, strongly correlated systems.Comment: 8 pages, 4 figure
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