1,606 research outputs found
Entanglement and quantum teleportation via decohered tripartite entangled states
The entanglement behavior of two classes of multi-qubit system, GHZ and GHZ
like states passing through a generalized amplitude damping channel is
discussed. Despite this channel causes degradation of the entangled properties
and consequently their abilities to perform quantum teleportation, one can
always improve the lower values of the entanglement and the fidelity of the
teleportrd state by controlling on Bell measurements, analyzer angle and
channel's strength. Using GHZ-like state within a generalized amplitude damping
channel is much better than using the normal GHZ-state, where the decay rate of
entanglement and the fidelity of the teleported states are smaller than those
depicted for GHZ state
Frozen accelerated information via local operations
In this contribution, we introduce a technique to freeze the parameters which
describe the accelerated states between two users to be used in the context of
quantum cryptography and quantum teleportation. It is assumed that, the two
users share different dimension sizes of particles, where we consider a
qubit-qutrit system. This technique depends on local operations, where it is
allowed that each particle interacts locally with a noisy phase channel. We
show that, the possibility of freezing the information of quantum channel
between the users depends on the initial state setting parameters, the initial
acceleration parameter strength of the phase channel. It is shown that, one may
increase the possibility of freezing the estimation degree of the parameters if
only the larger dimension system or both particles pass through the noisy phase
channel. Moreover, at small values of initial acceleration and large values of
the channel strength, the size of freezing estimation areas increases. The
results may be helpful in the context of quantum teleportation and quantum
coding
Fisher information of a single qubit interacts with a spin-qubit in the presence of a magnetic field
In this contribution, quantum Fisher information is utilized to estimate the
parameters of a central qubit interacting with a single-spin qubit. The effect
of the longitudinal, transverse and the rotating strengths of the magnetic
field on the estimation degree is discussed. It is shown that, in the resonance
case, the number of peaks and consequently the size of the estimation regions
increase as the rotating magnetic field strength increases. The precision
estimation of the central qubit parameters depends on the initial state
settings of the central and the spin- qubit, either encode classical or quantum
information. It is displayed that, the upper bounds of the estimation degree
are large if the two qubits encode classical information. In the non-resonance
case, the estimation degree depends on which of the longitudinal/transverse
strength is larger. The coupling constant between the central qubit and the
spin- qubit has a different effect on the estimation degree of the weight and
the phase parameters, where the possibility of estimating the weight parameter
decreases as the coupling constant increases, while it increases for the phase
parameter. For large number of spin-particles, namely, we have a spin-bath
particles, the upper bounds of the Fisher information with respect to the
weight parameter of the central qubit decreases as the number of the spin
particle increases. As the interaction time increases, the upper bounds appear
at different initial values of the weight parameter
Entanglement Routers via Wireless Quantum Network Based on Arbitrary Two Qubit Systems
A wireless quantum network is generated between multi-hop, where each hop
consists of two entangled nodes. These nodes share a finite number of entangled
two qubit systems randomly. Different types of wireless quantum bridges are
generated between the non-connected nodes. The efficiency of these wireless
quantum bridges to be used as quantum channels between its terminals to perform
quantum teleportation is investigated. We suggest a theoretical wireless
quantum communication protocol to teleport unknown quantum signals from one
node to another, where the more powerful wireless quantum bridges are used as
quantum channels. It is shown that, by increasing the efficiency of the sources
which emit the initial partial entangled states, one can increase the
efficiency of the wireless quantum communication protocol
Some properties of multi-qubit systems under effect of the Lorentz transformation
Effect of Lorentz transformation on some properties of multi-qubit systems is
investigated. It is shown that, properties like, the fidelity and entanglement
decay as the Wigner's angles increase, but can be improved, if all the
transformed particles are transformed with the same Wigner's angles. The upper
bounds of the average capacity of the GHZ state increases while it decreases
and more robust with the W-state as the Wigner's angle of the observer
decreases. Under Lorentz transformation, the tripartite states transform into
another equivalent states and hence no change on the efficiency of these states
to perform quantum information tasks
Immunity, Improving and Retrieving the lost entanglement of accelerated qubit-qutrit system via local Filtering
The possibility of immunized and improving the entanglement of accelerated
systems via local filtering is discussed. The maximum bounds of entanglement
depend on the dimensions of the accelerated and the filtered subsystems. If the
small dimensional subsystem is accelerated and the large dimensional subsystem
is filtered, one can get a long-lived entanglement. Moreover, if the larger
subsystem is accelerated, then by filtering any subsystem, the upper bounds of
entanglement of the filtered state are larger then that for the initial
states.For any accelerated subsystem, the entanglement always increases as the
filter strength of the large dimensional subsystem increases
Dynamics of multi-qubit systems in noisy environment
Some properties of multi-qubit systems interacting with noisy environment is
discussed. The amount of the survival entanglement is quantified for the GHZ
and W-states. It is shown that the entanglement decay depends on the noise type
( correlated or non-correlated), number of interacted qubits with the
environment and the initial state which passes through this noisy environment.
In general, the GHZ is more fragile than the W-state. The phenomena of
entanglement sudden death appears only for non-correlated noise
Information transfer and orthogonality speed via pulsed-driven qubit
We investigate the transfer and exchange information between a single qubit
system excited by a rectangular pulse. The dynamics of the system is treated
within and outside rotating wave approximation (RWA). The initial state of the
qubit plays an important role for sending information with high fidelity.
Within RWA, and as the fidelity of the transformed information increases the
exchange information with the environment increases. For increasing values of
atomic detuning, the fidelity decreases faster and the exchange information has
an upper limit. Outside RWA,the fidelity of the transformed information
increases as one increases the perturbation parameter. However the exchange
information is very high compared with that within RWA. The orthogonality speed
of the travelling qubit is investigated for different classes of initial atomic
state settings and field parameters.Comment: Accepted in " Nonlinear Optics, Quantum Optics: Concepts in Modern
Optics
Estimation of pulsed driven qubit parameters via quantum Fisher information
We estimate the initial weight and phase parameters ( of a
single qubit system initially prepared in the coherent state
and interacts with three different shape of pulses;
rectangular, exponential, and -pulses. In general, we show that the
estimation degree of the weight parameter depends on the pulse shape and the
initial phase angle, . For the rectangular pulse case, increasing the
estimating rate of the weight parameter via the Fisher information function
is possible with small values of the atomic detuning
parameter and larger values of the pulse strength.
Fisher information increases suddenly at resonant case
to reach its maximum value if the initial phase and consequently
one may estimate the phase parameter with high degree of precision. If the
initial system is coded with classical information, the upper bounds of Fisher
information for resonant and non-resonant cases are much larger and
consequently one may estimate the pahse parameter with high degree of
estimation. Similarly as the detuning increases the Fisher information
decreases and therefore the possibility of estimating the phase parameter
decreases. For exponential, and -pulses the Fisher information is
maximum () and consequently one can always
estimate the weight and the phase parameters with high degree
of precision
Dynamics of multi-modes maximum entangled coherent state over amplitude damping channel
The dynamics of maximum entangled coherent state travels through an amplitude
damping channel is investigated. For small values of the transmissivity rate
the travelling state is very fragile to this noise channel, where it suffers
from the phase flip error with high probability. The entanglement decays
smoothly for larger values of the transmissivity rate and speedily for smaller
values of this rate. As the number of modes increases, the travelling state
over this noise channel loses its entanglement hastily. The odd and even states
vanish at the same value of the field intensity
- …