2,324 research outputs found
FFLO oscillations and magnetic domains in the Hubbard model with off-diagonal Coulomb repulsion
We observe the effect of non-zero magnetization m onto the superconducting
ground state of the one dimensional repulsive Hubbard model with correlated
hopping X. For t/2 < X < 2t/3, the system first manifests
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) oscillations in the pair-pair
correlations. For m = m1 a kinetic energy driven macroscopic phase separation
into low-density superconducting domains and high-density polarized walls takes
place. For m > m2 the domains fully localize, and the system eventually becomes
a ferrimagnetic insulator.Comment: IOP RevTeX class, 18 pages, 13 composite *.eps figure
Non-Local Order Parameters as a Probe for Phase Transitions in the Extended Fermi-Hubbard Model
The Extended Fermi-Hubbard model is a rather studied Hamiltonian due to both
its many applications and a rich phase diagram. Here we prove that all the
phase transitions encoded in its one dimensional version are detectable via
non-local operators related to charge and spin fluctuations. The main advantage
in using them is that, in contrast to usual local operators, their asymptotic
average value is finite only in the appropriate gapped phases. This makes them
powerful and accurate probes to detect quantum phase transitions. Our results
indeed confirm that they are able to properly capture both the nature and the
location of the transitions. Relevantly, this happens also for conducting
phases with a spin gap, thus providing an order parameter for the
identification of superconducting and paired superfluid phasesComment: 7 pages, 3 figures; Submitted to EPJ Special Topics, Quantum Gases
and Quantum Coherenc
Encoding for the Blackwell Channel with Reinforced Belief Propagation
A key idea in coding for the broadcast channel (BC) is binning, in which the
transmitter encode information by selecting a codeword from an appropriate bin
(the messages are thus the bin indexes). This selection is normally done by
solving an appropriate (possibly difficult) combinatorial problem. Recently it
has been shown that binning for the Blackwell channel --a particular BC-- can
be done by iterative schemes based on Survey Propagation (SP). This method uses
decimation for SP and suffers a complexity of O(n^2). In this paper we propose
a new variation of the Belief Propagation (BP) algorithm, named Reinforced BP
algorithm, that turns BP into a solver. Our simulations show that this new
algorithm has complexity O(n log n). Using this new algorithm together with a
non-linear coding scheme, we can efficiently achieve rates close to the border
of the capacity region of the Blackwell channel.Comment: 5 pages, 8 figures, submitted to ISIT 200
Quantum Dynamics of Coupled Bosonic Wells within the Bose-Hubbard Picture
We relate the quantum dynamics of the Bose-Hubbard model (BHM) to the
semiclassical nonlinear equations that describe an array of interacting Bose
condensates by implementing a standard variational procedure based on the
coherent state method. We investigate the dynamics of the two-site BHM from the
purely quantum viewpoint by recasting first the model within a spin picture and
using then the related dynamical algebra. The latter allows us to study
thoroughly the energy spectrum structure and to interpret quantally the
classical symmetries of the two-site dynamics. The energy spectrum is also
evaluated through various approximations relying on the coherent state
approach.Comment: 22 pages, 7 figure
Spin-fermion mappings for even Hamiltonian operators
We revisit the Jordan-Wigner transformation, showing that --rather than a
non-local isomorphism between different fermionic and spin Hamiltonian
operators-- it can be viewed in terms of local identities relating different
realizations of projection operators. The construction works for arbitrary
dimension of the ambient lattice, as well as of the on-site vector space,
generalizing Jordan-Wigner's result. It provides direct mapping of local
quantum spin problems into local fermionic problems (and viceversa), under the
(rather physical) requirement that the latter are described by Hamiltonian's
which are even products of fermionic operators. As an application, we
specialize to mappings between constrained-fermions models and spin 1 models on
chains, obtaining in particular some new integrable spin Hamiltonian, and the
corresponding ground state energies.Comment: 7 pages, ReVTeX file, no figure
Quantum symmetries induced by phonons in the Hubbard model
We show how the addition of a phonon field to the Hubbard model deforms the superconducting su(2) part of the global symmetry Lie algebra su(2)⊗su(2)/openZ2, holding at half filling for the customary model, into a quantum [su(2)]q symmetry, holding for a filling which depends on the electron-phonon interaction strength. Such symmetry originates in the feature that in the presence of phonons the hopping amplitude turns out to depend on the coupling strength. The states generated by resorting to this q symmetry exhibit both off-diagonal long-range order and pairing
Rigorous results on superconducting ground state of attractive extended Hubbard models
We show that the exact ground state for a class of extended Hubbard models including bond-charge, exchange, and pair-hopping terms, is the Yang ''eta-paired'' state for any nonvanishing positive value of the pair-hopping amplitude, at least when the on-site Coulomb interaction is attractive enough and the remaining physical parameters satisfy a single constraint. The ground state is thus rigorously superconducting. Our result holds on a bipartite lattice in any dimension, at any band filling, and for arbitrary electron hopping
Classical realization of two-site Fermi-Hubbard systems
A classical wave optics realization of the two-site Hubbard model, describing
the dynamics of interacting fermions in a double-well potential, is proposed
based on light transport in evanescently-coupled optical waveguides.Comment: 4 page
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