18 research outputs found
Optimal teleportation via thermal entangled states of a two-qubit Heisenberg Chain
We study the optimal teleportation based on Bell measurements via the thermal
states of a two-qubit Heisenberg XXX chain in the presence of
Dzyaloshinsky-Moriya (DM) anisotropic antisymmetric interaction and obtain the
optimal unitary transformation. The explicit expressions of the output state
and the teleportation fidelity are presented and compared with those of the
standard protocol. It is shown that in this protocol the teleportation fidelity
is always larger and unit fidelity is achieved at zero temperature. The DM
interaction can enhance the teleportation fidelity at finite temperatures, as
opposed to the effect of the interaction in the standard protocol. Cases with
other types of anisotropies are also discussed.Comment: Accepted by EP
General approach of weak-to-strong measurement transition for Fock-state-based pointer states
The transition from von Neumann's projective strong measurement to Aharonov's
weak measurement has recently received large attention, theoretical and
experimental. In this work, we present a general approach to describe the
weak-to-strong measurement transition for Fock-state-based pointer pointer
states, and analyze in some details the case of coherent pointer states. A
possible realization of our measurement scheme using trapped ions is also
discussed.Comment: 12 pages,11 figure
Various Correlations in Anisotropic Heisenberg XYZ Model with Dzyaloshinski-Moriya Interaction
Various thermal correlations as well as the effect of intrinsic decoherence
on the correlations are studied in a two-qubit Heisenberg XYZ spin chain with
the Dzyaloshinski--Moriya (DM) interaction along the z direction, i.e. Dz. It
is found that tunable parameter Dz may play a constructive role on the
concurrence (C), classical correlation (CC) and quantum discord (QD) in thermal
equilibrium while it plays a destructive role on the correlations in the
intrinsic decoherence case. The entanglement and quantum discord exhibit
collapse and revival under the phase decoherence. With a proper combination of
the system parameters, the correlations can effectively be kept at high steady
state values despite the intrinsic decoherence.Comment: 4 pages, 4 figure
Quantum correlations in spin models
Bell nonlocality, entanglement and nonclassical correlations are different
aspects of quantum correlations for a given state. There are many methods to
measure nonclassical correlations. In this paper, nonclassical correlations in
two-qubit spin models are measured by use of measurement-induced disturbance
(MID) [Phys. Rev. A, 77, 022301 (2008)] and geometric measure of quantum
discord (GQD) [Phys. Rev. Lett. 105, 190502 (2010)]. Their dependencies on
external magnetic field, spin-spin coupling, and Dzyaloshinski-Moriya (DM)
interaction are presented in detail. We also compare Bell nonlocality,
entanglement measured by concurrence, MID and GQD and illustrate their
different characteristics.Comment: 1 text and 5 eps figures, accepted by Annals of Physic
Various correlations in a Heisenberg XXZ spin chain both in thermal equilibrium and under the intrinsic decoherence
In this paper we discuss various correlations measured by the concurrence
(C), classical correlation (CC), quantum discord (QD), and geometric measure of
discord (GMD) in a two-qubit Heisenberg XXZ spin chain in the presence of
external magnetic field and Dzyaloshinskii-Moriya (DM) anisotropic
antisymmetric interaction. Based on the analytically derived expressions for
the correlations for the cases of thermal equilibrium and the inclusion of
intrinsic decoherence, we discuss and compare the effects of various system
parameters on the correlations in different cases. The results show that the
anisotropy Jz is considerably crucial for the correlations in thermal
equilibrium at zero temperature limit but ineffective under the consideration
of the intrinsic decoherence, and these quantities decrease as temperature T
rises on the whole. Besides, J turned out to be constructive, but B be
detrimental in the manipulation and control of various quantities both in
thermal equilibrium and under the intrinsic decoherence which can be avoided by
tuning other system parameters, while D is constructive in thermal equilibrium,
but destructive in the case of intrinsic decoherence in general. In addition,
for the initial state , all
the correlations except the CC, exhibit a damping oscillation to a stable value
larger than zero following the time, while for the initial state , all the correlations monotonously
decrease, but CC still remains maximum. Moreover, there is not a definite
ordering of these quantities in thermal equilibrium, whereas there is a
descending order of the CC, C, GMD and QD under the intrinsic decoherence with
a nonnull B when the initial state is .Comment: 8 pages, 7 figure
Single-photon-added coherent state based measurement transition and its advantages in precision measurement
In this work, the measurement transition as well as precision measurement
advantages of single-photon-added coherent state after postselected von Neumann
measurement are investigated. We noticed that the weak-to-strong measurement
transition characterized by the shifts of pointer's position and momentum
variables occurred in continuously by controlling a dimensionless parameter
associated with system-pointer coupling. We calculate the ratio between the
signal-to-noise ratio of nonpostselected and postselected measurements, and the
latter is used to find the quantum Fisher information. We found that the
single-photon-added coherent pointer state can improve the precision of the
measurement processes such as signal-to-noise ratio and parameter estimation
after postselected von Neumann measurement characterized by postselection and
weak value. Furthermore, contrary to the results of several previous studies,
we found that the anomalous large weak values can't improve the precision
measurement processes related to single-photon-added coherent state.Comment: 9pages, 6 figure