14 research outputs found
Generation of entanglement in systems of intercoupled qubits
We consider systems of two and three qubits, mutually coupled by
Heisenberg-type exchange interaction and interacting with external laser
fields. We show that these systems allow one to create maximally entangled Bell
states, as well as three qubit Greenberger-Horne-Zeilinger and W states. In
particular, we point out that some of the target states are the eigenstates of
the initial bare system. Due to this, one can create entangled states by means
of pulse area and adiabatic techniques, when starting from a separable
(non-entangled) ground state. On the other hand, for target states, not present
initially in the eigensystem of the model, we apply the robust stimulated Raman
adiabatic passage and pulse techniques, that create desired coherent
superpositions of non-entangled eigenstates.Comment: 9 pages, 7 figures. Updated version for publicatio
Magnetic and thermodynamic properties of the octanuclear nickel phosphonate-based cage
We report a detailed theoretical investigation into the influence of
anisotropy on the magnetic and thermodynamic properties of an octanuclear
nickel phosphonate cage with butterfly-shaped molecular geometry, namely
. To validate our exact
diagonalization approach, we firstly compare results with simulations and
experiment in the isotropic case. Having established concurrence, we then
introduce uniaxial single-ion anisotropy and Heisenberg exchange anisotropy
between interacted nickel atoms. We then examine effects of both anisotropy
parameters on the magnetization process, as well as on the specific heat of the
model. We predict intermediate magnetization plateaus, including zero plateau,
and magnetization jumps with magnetic ground-state phase transitions at low
temperature K. The magnetization plateaus are strongly dependent on both
the levels of exchange anisotropy and single-ion anisotropy. Varying the former
leads to change in width and magnetic position of all intermediate plateaus
while they become wider upon increasing the latter. The specific heat of the
model manifests a Schottky-type maximum at moderate temperature in the presence
of weak magnetic fields, when the system is isotropic. The introducion of
aniostropy results in substantial variations in the thermal behavior of the
specific heat. Indeed, by tuning anisotropy parameters the Schottky peak
convert to a double-peak temperature dependence that coincided with the
magnetization jumps. We call for these theoretical predictions to be verified
experimentally at low temperature.Comment: 16 pages, 4 figure
Diamond chain with delocalized interstitial spins: Magnetization, thermal and entanglement properties
We study physical properties of the symmetric diamond chain with delocalized interstitial spins. We derive an exact solution of the model and characterize the phases of the system at zero temperature. On the basis of this solution, we examine its magnetic and thermal properties as well. The case of nonconserved electron number is then considered. There are phases, which we term as nonclassical, for which electrons in Hubbard dimers are in quantum entangled states. We finally study quantum entanglement depending on Hamiltonian parameters and temperature. </jats:p
Partition function zeros and magnetization plateaus of the spin-1 IsingāHeisenberg diamond chain
The specific heat and magnetic properties of two species of spin-1/2 ladders with butterfly-shaped unit blocks
The specific heat, structural characterization, and magnetic property studies
of a new spin ladder with the geometry of butterfly-shaped configuration are
reported. The model introduced here is an infinite spin ladder-type including
spin-1/2 particle for which unit blocks consist of two butterflies connected
together through their bodies (Body-Body bridges). Localized spins on the wings
of butterflies have XXZ Heisenberg interaction with two extra spin-1/2
particles assumed in the center of each cage (unit block), while they have pure
Ising-type interaction with those spins that are localized on the bodies.
Hence, there are six interstitial spins and four nodal spins (Body-Body
interaction) per block. To obtain the partition function of this model, we use
the transfer matrix approach, then we examine the magnetization process, as
well as, the specific heat of the model. Interestingly, we see a wide plateau
at of the saturation magnetization that is strongly dependent on
the magnetic field and anisotropy variations. Moreover, some unexpected
phenomena are observed in the low-temperature limit, such as anomalous
triple-peak in the specific heat function which gradually turns to a
double-peak upon increasing the magnetic field and/or anisotropic Heisenberg
coupling, due to the ferromagnetic phase predomination.Comment: 5 pages, 3 figure