19 research outputs found
Thermal entanglement and efficiency of the quantum Otto cycle for the su(1,1) Tavis-Cummings system
The influence of the dynamical Stark shift on the thermal entanglement and
the efficiency of the quantum Otto cycle is studied for the su(1,1)
Tavis-Cummings system. It is shown that the degree of the thermal entanglement
becomes larger as the dynamical Stark shift increases. In contrast, the
efficiency of the Otto cycle is degraded with an increase of the values of
dynamical Stark shift. Expressions for the efficiency coefficient are derived.
Using those expressions we identify the maximal efficiency of the quantum Otto
cycle from the experimentally measured values of the dynamical Stark shiftComment: to appear in J.Phys.
Positive-Negative Birefringence in Multiferroic Layered Metasurfaces
We uncover and identify the regime for a magnetically and ferroelectrically
controllable negative refraction of light traversing multiferroic, oxide-based
metastructure consisting of alternating nanoscopic ferroelectric (SrTiO)
and ferromagnetic (YFe(FeO), YIG) layers. We perform analytical
and numerical simulations based on discretized, coupled equations for the
self-consistent Maxwell/ferroelectric/ferromagnetic dynamics and obtain a
biquadratic relation for the refractive index. Various scenarios of ordinary
and negative refraction in different frequency ranges are analyzed and
quantified by simple analytical formula that are confirmed by full-fledge
numerical simulations. Electromagnetic-waves injected at the edges of the
sample are propagated exactly numerically. We discovered that for particular
GHz frequencies, waves with different polarizations are characterized by
different signs of the refractive index giving rise to novel types of phenomena
such as a positive-negative birefringence effect, and magnetically controlled
light trapping and accelerations
Entanglement balance of quantum scattering processes
The theory of quantum information constitutes the functional value of the
quantum entanglement, i.e., quantum entanglement is essential for high fidelity
of quantum protocols, while fundamental physical processes behind the formation
of quantum entanglement are less relevant for practical purposes. In the
present work, we explore physical mechanisms leading to the emergence of
quantum entanglement in the initially disentangled system. In particular, we
analyze spin entanglement of outgoing electrons in a nonrelativistic quantum
collision on a target with one active electron. Our description
exploits the time-dependent scattering formalism for typical conditions of
scattering experiments, and contrary to the customary stationary formalism
operates with realistic scattering states. We quantify the spin entanglement in
the final scattering channel through the pair concurrence and express it in
terms of the experimentally measurable spin-resolved triple
differential cross sections. Besides, we consider Bell's inequality and inspect
the regimes of its violation in the final channel. We address both the pure and
the mixed initial spin state cases and uncover kinematical conditions of the
maximal entanglement of the outgoing electron pair. The numerical results for
the pair concurrence, entanglement of formation, and violation of Bell's
inequality obtained for the ionization process of atomic hydrogen show
that the entangled electron pairs indeed can be formed in the
collisions even with spin-unpolarized projectile and target electrons in the
initial channel. The positive entanglement balance---the difference between
entanglements of the initial and final electron pairs---can be measured in the
experiment.Comment: 31 pages, 6 figure
A Comprehensible Review: Magnonic Magnetoelectric Coupling in Ferroelectric/ Ferromagnetic Composites
Composite materials consisting of coupled magnetic and ferroelectric layers
hold the promise for new emergent properties such as controlling magnetism with
electric fields. Obviously, the interfacial coupling mechanism plays a crucial
role and its understanding is the key for exploiting this material class for
technological applications. This short review is focused on the magnonic-based
magnetoelectric coupling that forms at the interface of a metallic ferromagnet
with a ferroelectric insulator. After analyzing the physics behind this
coupling, the implication for the magnetic, transport, and optical properties
of these composite materials is discussed. Furthermore, examples for the
functionality of such interfaces are illustrated by the electric field
controlled transport through ferroelectric/ferromagnetic tunnel junctions, the
electrically and magnetically controlled optical properties, and the generation
of electromagnon solitons for the use as reliable information carriers.Comment: Physica Status Solidi B 1, 1900750 (2020
Self-Chaotization in Coupled Optical Waveguides
We consider theoretically two coupled optical waveguides with a varying
barrier height along the waveguides direction. The barrier could be constructed
by the elongated island with a reduced refractive index (which acts as a
potential barrier), such that in the middle region it splits a waveguide into
two weakly coupled parts. It is predicted by numerical simulations and
analytical consideration that the presence of some imperfection of the system
parameters can cause splitting of injected laser beam and one will observe two
intensity maximums at the output, while for small imperfections the input and
output beam intensity distributions will be the same. The switching between two
regimes could be achieved changing spectral width of the beam or refractive
index of the island. This nontrivial effect is explained by possibility of
transitions between the different eigenstates of the system in the region of
large potential barrier heights. The mentioned effect could be used for
all-optical readdressing and filtering purposes