161 research outputs found
A Revisit to Non-maximally Entangled Mixed States: Teleportation Witness, Noisy Channel and Discord
We constructed a class of non-maximally entangled mixed states \cite{roy2010}
and extensively studied its entanglement properties and also their usefulness
as teleportation channels. In this article, we revisited our constructed state
and have studied it from three different perspectives. Since every entangled
state is associated with an witness operator, we have found a suitable
entanglement as well as teleportation witness for our non-maximally entangled
mixed states. We considered the noisy channel's effects on our constructed
state and to see whether it affects the states' capacity as teleportation
channel. For this purpose we have mainly emphasized on amplitude damping
channel. A comparative study with concurrence and quantum discord of the state
of ref. \cite{roy2010} has also been carried out here.Comment: 11 pages, 4 figure
Study of controlled dense coding with some discrete tripartite and quadripartite states
The paper presents the detailed study of controlled dense coding scheme for
different types of and particle states. It consists of GHZ state, GHZ
type states, Maximal Slice state, Four particle GHZ state and W class of
states. It is shown that GHZ-type states can be used for controlled dense
coding in a probabilistic sense. We have shown relations among parameter of GHZ
type state, concurrence of the shared bipartite state by two parties with
respect to GHZ type and Charlie's measurement angle . We have seen that
tripartite W state and quadripartite W state cannot be used in controlled dense
coding whereas states can be used probabilistically.
Finally, we have investigated controlled dense coding scheme for tripartite
qutrit states.Comment: 21 pages, 7 figures, Accepted in International Journal of Quantum
Information on 8th of June 201
Operational criterion for controlled dense coding with non-trivial tripartite entangled states
In this paper, we provide an operational criterion for controlled dense
coding with a general class of three-qubit partially entangled states. A
general three-qubit pure entangled state can be classified into two
inequivalent classes according to their genuine tripartite entanglement. We
claim that if a three-qubit state shows entanglement characteristic similar to
-class then such non-trivial tripartite states are useful in {\it
controlled dense coding} whereas states belonging to -class are not useful
for that. We start with a particular class of non-trivial partially entangled
states belonging to -class and show that they are effective in controlled
dense coding. Then we cite several other examples of different types of
tripartite entangled states to support our conjecture.Comment: Accepted for publication in "Pramana Journal of Physics", (Indian
Academy of Sciences, Springer
Control of atomic entanglement by dynamic Stark effect
We study the entanglement properties of two three-level Rydberg atoms passing
through a single-mode cavity. The interaction of an atom with the cavity field
allows the atom to make a transition from the upper most (lower most) to the
lower most (upper most) level by emission (absoprtion) of two photons via the
middle level. We employ an effective Hamiltonian that describes the system with
a Stark shifted two-photon atomic transition. We compute the entanglement of
formation of the joint two-atom state as a function of Rabi angle . It is
shown that the Stark shift can be used to enhance the magnitude of atomic
entanglement over that obtained in the resonant condition for certain parameter
values. We find that though the two-atom entanglement generally diminishes with
the increase of the two-photon detuning and the Stark shift, it is possible to
sustain the entanglement over a range of interaction times by making the
detuning and the Stark shift compensate each other. Similar characteristics are
obtained for a thermal state cavity field too.Comment: 7 pages, Revtex, 6 eps figure
Effects of cavity-field statistics on atomic entanglement in the Jaynes-Cummings model
We study the entanglement properties of a pair of two-level atoms going
through a cavity one after another. The initial joint state of two successive
atoms that enter the cavity is unentangled. Interactions mediated by the cavity
photon field result in the final two-atom state being of a mixed entangled
type. We consider the field statistics of the Fock state field, and the thermal
field, respectively, inside the cavity. The entanglement of formation of the
joint two-atom state is calculated for both these cases as a function of the
Rabi-angle . We present a comparitive study of two-atom entanglement for
low and high mean photon number cases corresponding to the different fields
statistics.Comment: 10 pages, 3 eps figure
Information transfer in leaky atom-cavity systems
We consider first a system of two enatangled cavities and a single two-level
atom passing through one of them. A ``monogamy'' inequality for this tripartite
system is quantitatively studied and verified in the presence of cavity
leakage. We next consider the simultaneous passage of two-level atoms through
both the cavities. Entanglement swapping is observed between the two-cavity and
the two-atom system. Cavity dissipation leads to the quantitative reduction of
information transfer though preserving the basic swapping property.Comment: Latex, 14 pages, 8 .eps figure
Atomic entanglement mediated by a squeezed cavity field
We consider the coherent state radiation field inside a micromaser cavity and
study the entanglement mediated by it on a pair of two level atoms passing
though the cavity one after the other. We then investigate the effects of
squeezing of the cavity field on the atomic entanglement. We compute the
entanglement of formation for the emerging mixed two-atom state and show that
squeezing of the cavity radiation field can increase the atomic entanglement.Comment: 6 pages, 7 eps figure
A first principles study of magnetism in PdFe under pressure
Recent experiments on PdFe intermetallics [Phys. Rev. Lett. 102, 237202
(2009)] have revealed that the system behaves like a classical invar alloy
under high pressure. The experimental pressure-volume relation suggests an
anomalous volume collapse and a substantial increase in bulk modulus around the
pressure where invar behavior is observed. With the help of first-principles
density functional theory based calculations, we have explored various magnetic
phases (ferromagnetic, fully and partially disordered local moment, spin
spiral) in order to understand the effect of pressure on magnetism. Our
calculations reveal that the system does not undergo a transition from a
ferromagnetic to a spin-disordered state as was thought to be the possible
mechanism to explain the invar behavior of this system. We rather suggest that
the anomaly in the system could possibly be due to the transition from a
collinear state to non-collinear magnetic states upon the application of
pressure.Comment: 8 pages, 10 figure
Anti-site disorder and improved functionality of MnNi{\it X} ({\it X}= Al, Ga, In, Sn) inverse Heusler alloys
Recent first-principles calculations have predicted MnNi{\it X} ({\it
X}=Al, Ga, In, Sn) alloys to be magnetic shape memory alloys. Moreover,
experiments on MnNiGa and MnNiSn suggest that the alloys deviate
from the perfect inverse Heusler arrangement and that there is chemical
disorder at the sublattices with tetrahedral symmetry. In this work, we
investigate the effects of such chemical disorder on phase stabilities and
magnetic properties using first-principles electronic structure methods. We
find that except MnNiAl, all other alloys show signatures of martensitic
transformations in presence of anti-site disorder at the sublattices with
tetrahedral symmetry. This improves the possibilities of realizing martensitic
transformations at relatively low fields and the possibilities of obtaining
significantly large inverse magneto-caloric effects, in comparison to perfect
inverse Heusler arrangement of atoms. We analyze the origin of such
improvements in functional properties by investigating electronic structures
and magnetic exchange interactions
A new first principles approach to calculate phonon spectra of disordered alloys
The lattice dynamics in substitutional disordered alloys with constituents
having large size differences is driven by strong disorder in masses,
inter-atomic force constants and local environments. In this letter, a new
first-principles approach based on special quasi random structures and
itinerant coherent potential approximation to compute the phonon spectra of
such alloys is proposed and applied to NiPt alloy. The
agreement between our results with the experiments is found to be much better
than for previous models of disorder due to an accurate treatment of the
interplay of inter-atomic forces among various pairs of chemical species. This
new formalism serves as a potential solution to the longstanding problem of a
proper microscopic understanding of lattice dynamical behavior of disordered
alloys.Comment: 10 pages, 2 figure
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