27 research outputs found
Some exact results for the zero-bandwidth extended Hubbard model with intersite charge and magnetic interactions
The extended Hubbard model in the zero-bandwidth limit is studied. The
effective Hamiltonian consists of (i) on-site interaction and intersite
(ii) density-density interaction and (iii) Ising-like magnetic exchange
interaction (between the nearest-neighbors). We present rigorous (and
analytical) results obtained within the transfer-matrix method for 1D-chain in
two particular cases: (a) and ; (b) and
(, ). We obtain the exact formulas for the partition
functions which enables to calculate thermodynamic properties such as entropy,
specific heat (), and double occupancy per site. In both cases the system
exhibits an interesting temperature dependence of involving a
characteristic two-peak structure. There are no phase transitions at finite
temperatures and the only transitions occur in the ground state.Comment: 4 pages, 2 figures; pdf-ReVTeX; updated references; presented at The
European Conference PHYSICS OF MAGNETISM 2014 (PM'14), June 23-27, 2014,
Poznan, Poland; submitted to Acta Physica Polonica
Nonlocality activation in entanglement swapping chains
We consider multiple entanglement swappings performed on a chain of bipartite
states. Each state does not violate CHSH inequality. We show that before some
critical number of entanglement swappings is achieved the output state does not
violate this inequality either. However, if this number is achieved then for
some results of Bell measurements obtained in the protocol of entanglement
swapping the output state violates CHSH inequality. Moreover, we show that for
different states we have different critical numbers for which CHSH inequality
is activated.Comment: 4 page
Interplay between charge and magnetic orderings in the zero-bandwidth limit of the extended Hubbard model for strong on-site repulsion
A simple effective model of charge ordered and (or) magnetically ordered
insulators is studied. The tight binding Hamiltonian analyzed consists of (i)
the effective on-site interaction U, (ii) the intersite density-density
interaction W and (iii) intersite magnetic exchange interaction Jz (or Jxy)
between nearest-neighbors. The intersite interaction are treated within the
mean-field approximation. One shows that the systems considered can exhibit
very interesting multicritical behaviors, including among others bicritical,
tricritical, tetracritical and critical end points. The analysis of the model
has been performed for an arbitrary electron concentration as well as an
arbitrary chemical potential in the limit of strong on-site repulsion. The
phase diagrams obtained in such a case are shown to consist of at least 9
different states, including four homogenous phases: nonordered (NO),
ferromagnetic (F), charge ordered (CO), ferrimagnetic (intermediate, I) and
five types of phase separation: NO-NO, F-NO, F-F, CO-F, CO-I.Comment: 3 pages, 5 figures, pdf-ReVTeX, presented at The European Conference
Physics of Magnetism 2011, June 27 - July 1, 2011, Poznan, Polan
The Conditional Uncertainty Principle
We develop a general operational framework that formalizes the concept of
conditional uncertainty in a measure-independent fashion. Our formalism is
built upon a mathematical relation which we call conditional majorization. We
define conditional majorization and, for the case of classical memory, we
provide its thorough characterization in terms of monotones, i.e., functions
that preserve the partial order under conditional majorization. We demonstrate
the application of this framework by deriving two types of memory-assisted
uncertainty relations: (1) a monotone-based conditional uncertainty relation,
(2) a universal measure-independent conditional uncertainty relation, both of
which set a lower bound on the minimal uncertainty that Bob has about Alice's
pair of incompatible measurements, conditioned on arbitrary measurement that
Bob makes on his own system. We next compare the obtained relations with their
existing entropic counterparts and find that they are at least independent.Comment: 5 pages main + 10 pages appendix. Changes since v1: new results
demonstrating independence of our results from existing conditional
uncertainty relations; significant revision in notation and presentation;
expanded bibliograph
Entanglement witnessing and quantum cryptography with non-ideal ferromagnetic detectors
We investigate theoretically the use of non-ideal ferromagnetic contacts as a
mean to detect quantum entanglement of electron spins in transport experiments.
We use a designated entanglement witness and find a minimal spin polarization
of required to demonstrate spin entanglement.
This is significantly less stringent than the ubiquitous tests of Bell's
inequality with . In addition, we discuss the
impact of decoherence and noise on entanglement detection and apply the
presented framework to a simple quantum cryptography protocol. Our results are
directly applicable to a large variety of experiments.Comment: 10 pages, 4 figure