52 research outputs found
Doped two orbital chains with strong Hund's rule couplings - ferromagnetism, spin gap, singlet and triplet pairings
Different models for doping of two-orbital chains with mobile
fermions and strong, ferromagnetic (FM) Hund's rule couplings stabilizing the
S=1 spins are investigated by density matrix renormalization group (DMRG)
methods. The competition between antiferromagnetic (AF) and FM order leads to a
rich phase diagram with a narrow FM region for weak AF couplings and strongly
enhanced triplet pairing correlations. Without a level difference between the
orbitals, the spin gap persists upon doping, whereas gapless spin excitations
are generated by interactions among itinerant polarons in the presence of a
level difference. In the charge sector we find dominant singlet pairing
correlations without a level difference, whereas upon the inclusion of a
Coulomb repulsion between the orbitals or with a level difference, charge
density wave (CDW) correlations decay slowest. The string correlation functions
remain finite upon doping for all models.Comment: 9pages, 9figure
Entanglement of two-mode Bose-Einstein condensates
We investigate the entaglement characteristics of two general bimodal
Bose-Einstein condensates - a pair of tunnel-coupled Bose-Einstein condensates
and the atom-molecule Bose-Einstein condensate. We argue that the entanglement
is only physically meaningful if the system is viewed as a bipartite system,
where the subsystems are the two modes. The indistinguishibility of the
particles in the condensate means that the atomic constituents are physically
inaccessible and thus the degree of entanglement between individual particles,
unlike the entanglement between the modes, is not experimentally relevant so
long as the particles remain in the condensed state. We calculate the
entanglement between the modes for the exact ground state of the two bimodal
condensates and consider the dynamics of the entanglement in the tunnel-coupled
case.Comment: 11 pages, 8 figures, submitted to Physical Review A, to be presented
at the third UQ Mathematical Physics workshop, Oct. 4-6; changes made in
response to referee comment
Entanglement and nonlocality in multi-particle systems
Entanglement, the Einstein-Podolsky-Rosen (EPR) paradox and Bell's failure of
local-hidden-variable (LHV) theories are three historically famous forms of
"quantum nonlocality". We give experimental criteria for these three forms of
nonlocality in multi-particle systems, with the aim of better understanding the
transition from microscopic to macroscopic nonlocality. We examine the
nonlocality of N separated spin J systems. First, we obtain multipartite Bell
inequalities that address the correlation between spin values measured at each
site, and then we review spin squeezing inequalities that address the degree of
reduction in the variance of collective spins. The latter have been
particularly useful as a tool for investigating entanglement in Bose-Einstein
condensates (BEC). We present solutions for two topical quantum states:
multi-qubit Greenberger-Horne-Zeilinger (GHZ) states, and the ground state of a
two-well BEC
Exposure to aircraft and road traffic noise and associations with heart disease and stroke in six European countries: a cross-sectional study
This work was supported by the Economic and Social Research Council (grant ES/F038763/1) with additional funding from the European Network for Noise and Health (ENNAH, EU FP7 grant number 226442)
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