92 research outputs found
Phase separation and pairing regimes in the one-dimensional asymmetric Hubbard model
We address some open questions regarding the phase diagram of the
one-dimensional Hubbard model with asymmetric hopping coefficients and balanced
species. In the attractive regime we present a numerical study of the passage
from on-site pairing dominant correlations at small asymmetries to
charge-density waves in the region with markedly different hopping
coefficients. In the repulsive regime we exploit two analytical treatments in
the strong- and weak-coupling regimes in order to locate the onset of phase
separation at small and large asymmetries respectively.Comment: 13 pages, RevTeX 4, 12 eps figures, some additional refs. with
respect to v1 and citation errors fixe
Pairing, crystallization and string correlations of mass-imbalanced atomic mixtures in one-dimensional optical lattices
We numerically determine the very rich phase diagram of mass-imbalanced
binary mixtures of hardcore bosons (or equivalently -- fermions, or
hardcore-Bose/Fermi mixtures) loaded in one-dimensional optical lattices.
Focusing on commensurate fillings away from half filling, we find a strong
asymmetry between attractive and repulsive interactions. Attraction is found to
always lead to pairing, associated with a spin gap, and to pair crystallization
for very strong mass imbalance. In the repulsive case the two atomic components
remain instead fully gapless over a large parameter range; only a very strong
mass imbalance leads to the opening of a spin gap. The spin-gap phase is the
precursor of a crystalline phase occurring for an even stronger mass imbalance.
The fundamental asymmetry of the phase diagram is at odds with recent
theoretical predictions, and can be tested directly via time-of-flight
experiments on trapped cold atoms.Comment: 4 pages, 4 figures + Supplementary Materia
Real-time dynamics of lattice gauge theories with a few-qubit quantum computer
Gauge theories are fundamental to our understanding of interactions between
the elementary constituents of matter as mediated by gauge bosons. However,
computing the real-time dynamics in gauge theories is a notorious challenge for
classical computational methods. In the spirit of Feynman's vision of a quantum
simulator, this has recently stimulated theoretical effort to devise schemes
for simulating such theories on engineered quantum-mechanical devices, with the
difficulty that gauge invariance and the associated local conservation laws
(Gauss laws) need to be implemented. Here we report the first experimental
demonstration of a digital quantum simulation of a lattice gauge theory, by
realising 1+1-dimensional quantum electrodynamics (Schwinger model) on a
few-qubit trapped-ion quantum computer. We are interested in the real-time
evolution of the Schwinger mechanism, describing the instability of the bare
vacuum due to quantum fluctuations, which manifests itself in the spontaneous
creation of electron-positron pairs. To make efficient use of our quantum
resources, we map the original problem to a spin model by eliminating the gauge
fields in favour of exotic long-range interactions, which have a direct and
efficient implementation on an ion trap architecture. We explore the Schwinger
mechanism of particle-antiparticle generation by monitoring the mass production
and the vacuum persistence amplitude. Moreover, we track the real-time
evolution of entanglement in the system, which illustrates how particle
creation and entanglement generation are directly related. Our work represents
a first step towards quantum simulating high-energy theories with atomic
physics experiments, the long-term vision being the extension to real-time
quantum simulations of non-Abelian lattice gauge theories
Atomic Quantum Simulation of Dynamical Gauge Fields coupled to Fermionic Matter: From String Breaking to Evolution after a Quench
Using a Fermi-Bose mixture of ultra-cold atoms in an optical lattice, we
construct a quantum simulator for a U(1) gauge theory coupled to fermionic
matter. The construction is based on quantum links which realize continuous
gauge symmetry with discrete quantum variables. At low energies, quantum link
models with staggered fermions emerge from a Hubbard-type model which can be
quantum simulated. This allows us to investigate string breaking as well as the
real-time evolution after a quench in gauge theories, which are inaccessible to
classical simulation methods.Comment: 14 pages, 5 figures. Main text plus one general supplementary
material and one basic introduction to the topic. Published versio
Supplementation of Boswellia serrata and Salix alba Extracts during the Early Laying Phase: Effects on Serum and Albumen Proteins, Trace Elements, and Yolk Cholesterol
Abstract: Extracts from Boswellia serrata (Bs) and Salix alba (Sa) are used as supplement in poultry feed. The aims of this research were to study possible effects of a dietary supplementation with Bs and Sa on serum and albumen proteins, zinc and iron, and yolk cholesterol content in Leg-horn hens during the critical phase of the onset of laying. A total of 120 pullets, 17 weeks of age, were assigned to 2 groups (Control (C) and Treated (T), n = 60 each). The T group received a diet supplemented with 0.3% of dry extracts of Bs (5%) and Sa (5%) for 12 weeks. The study lasted 19 weeks. Serum proteins were fractionated using agarose gel electrophoresis (AGE) and SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Trace elements were determined in serum using atomic absorption spectrometry and yolk cholesterol was determined using a colorimetric test. No significant differences were observed between control and supplemented hens for ana-lyzed biochemical indices. Moreover, the supplementation with phytoextracts did not negative-ly affect the physiological variations of serum proteins therefore it can be safely used as a treatment to prevent inflammatory states at onset and during the early laying phase
Dimer, trimer and FFLO liquids in mass- and spin-imbalanced trapped binary mixtures in one dimension
We present a systematic investigation of attractive binary mixtures in
presence of both spin- and mass-imbalance in one dimensional setups described
by the Hubbard model. After discussing typical cold atomic experimental
realizations and the relation between microscopic and effective parameters, we
study several many-body features of trapped Fermi-Fermi and Bose-Bose mixtures
such as density profiles, momentum distributions and correlation functions by
means of numerical density-matrix-renormalization-group and Quantum Monte Carlo
simulations. In particular, we focus on the stability of
Fulde-Ferrell-Larkin-Ovchinnikov, dimer and trimer fluids in inhomogeneous
situations, as typically realized in cold gas experiments due to the harmonic
confinement. We finally consider possible experimental signatures of these
phases both in the presence of a finite polarization and of a finite
temperature.Comment: 19 pages, 25 figure
New detrital petrographic and thermochronologic constraints on the Late Cretaceous-Neogene erosional history of the equatorial margin of Brazil: Implications for the surface evolution of a complex rift margin
The equatorial margin of Brazil is an example of a rift margin with a complex landscape, dominated by an escarpment perpendicular to the continental margin, which testifies to an equally complex rift and post-rift surface and tectonic evolution. This has been the focus of a long debate on the driving mechanism for post-rift tectonics and on the amount of exhumation. This study contributes to this debate with new petrographic and thermochronologic data on 152 samples from three basins, Para-Maranhao, Barreirinhas and Ceara, on the offshore continental platform. Our detrital record goes back to the rift time at ca. 100 Ma ago and outlines three major evolutionary phases of a changing landscape: a rift phase, with the erosion of a moderate rift escarpment, a Late Cretaceous-Palaeogene post-rift phase of major drainage reorganization and significant vertical erosion and a Late Oligocene-to-Recent post-rift phase of moderate vertical erosion and river headwater migration. We estimate that along the equatorial margin of Brazil, over a large onshore area, exhumation since the Late Cretaceous has totalled locally up to 2-2.5 km and since the late Oligocene did not exceed 1 km
Observation of chiral edge states with neutral fermions in synthetic Hall ribbons
Chiral edge states are a hallmark of quantum Hall physics. In electronic systems, they appear as a macroscopic consequence of the cyclotron orbits induced by a magnetic field, which are naturally truncated at the physical boundary of the sample. Here we report on the experimental realization of chiral edge states in a ribbon geometry with an ultracold gas of neutral fermions subjected to an artificial gauge field. By imaging individual sites along a synthetic dimension, encoded in the nuclear spin of the atoms, we detect the existence of the edge states and observe the edge-cyclotron orbits induced during quench dynamics. The realization of fermionic chiral edge states opens the door for edge state interferometry and the study of non-Abelian anyons in atomic systems
Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons
One of the most remarkable results of quantum mechanics is the fact that
many-body quantum systems may exhibit phase transitions even at zero
temperature. Quantum fluctuations, deeply rooted in Heisenberg's uncertainty
principle, and not thermal fluctuations, drive the system from one phase to
another. Typically, the relative strength of two competing terms in the
system's Hamiltonian is changed across a finite critical value. A well-known
example is the Mott-Hubbard quantum phase transition from a superfluid to an
insulating phase, which has been observed for weakly interacting bosonic atomic
gases. However, for strongly interacting quantum systems confined to
lower-dimensional geometry a novel type of quantum phase transition may be
induced for which an arbitrarily weak perturbation to the Hamiltonian is
sufficient to drive the transition. Here, for a one-dimensional (1D) quantum
gas of bosonic caesium atoms with tunable interactions, we observe the
commensurate-incommensurate quantum phase transition from a superfluid
Luttinger liquid to a Mott-insulator. For sufficiently strong interactions, the
transition is induced by adding an arbitrarily weak optical lattice
commensurate with the atomic granularity, which leads to immediate pinning of
the atoms. We map out the phase diagram and find that our measurements in the
strongly interacting regime agree well with a quantum field description based
on the exactly solvable sine-Gordon model. We trace the phase boundary all the
way to the weakly interacting regime where we find good agreement with the
predictions of the 1D Bose-Hubbard model. Our results open up the experimental
study of quantum phase transitions, criticality, and transport phenomena beyond
Hubbard-type models in the context of ultracold gases
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