34 research outputs found
Coherent State Control of Non-Interacting Quantum Entanglement
We exploit a novel approximation scheme to obtain a new and compact formula
for the parameters underlying coherent-state control of the evolution of a pair
of entangled two-level systems. It is appropriate for long times and for
relatively strong external quantum control via coherent state irradiation. We
take account of both discrete-state and continuous-variable degrees of freedom.
The formula predicts the relative heights of entanglement revivals and their
timing and duration.Comment: Published in PRA, 10 pages, 7 figure
Entanglement sudden death and sudden birth in two uncoupled spins
We investigate the entanglement evolution of two qubits interacting with a
common environment trough an Heisenberg XX mechanism. We reveal the possibility
of realizing the phenomenon of entanglement sudden death as well as the
entanglement sudden birth acting on the environment. Such analysis is of
maximal interest at the light of the large applications that spin systems have
in quantum information theory
Entanglement dynamics of two-qubit system in different types of noisy channels
In this paper, we study entanglement dynamics of a two-qubit extended
Werner-like state locally interacting with independent noisy channels, i.e.,
amplitude damping, phase damping and depolarizing channels. We show that the
purity of initial entangled state has direct impacts on the entanglement
robustness in each noisy channel. That is, if the initial entangled state is
prepared in mixed instead of pure form, the state may exhibit entanglement
sudden death (ESD) and/or be decreased for the critical probability at which
the entanglement disappear.Comment: 11 pages, 6 figure
Atomic entanglement sudden death in a strongly driven cavity QED system
We study the entanglement dynamics of strongly driven atoms off-resonantly
coupled with cavity fields. We consider conditions characterized not only by
the atom-field coupling but also by the atom-field detuning. By studying two
different models within the framework of cavity QED, we show that the so-called
atomic entanglement sudden death (ESD) always occurs if the atom-field coupling
lager than the atom-field detuning, and is independent of the type of initial
atomic state
A Study on the Sudden Death of Entanglement
The dynamics of entanglement and the phenomenon of entanglement sudden death
(ESD) \cite{yu} are discussed in bipartite systems, measured by Wootters
Concurrence. Our calculation shows that ESD appears whenever the system is open
or closed and is dependent on the initial condition. The relation of the
evolution of entanglement and energy transfer between the system and its
surroundings is also studied.Comment: Comments and criticism are welcome. Accepted by Phys. Lett.
Quantum recoil effects in finite-time disentanglement of two distinguishable atoms
Starting from the requirement of distinguishability of two atoms by their
positions, it is shown that photon recoil has a strong influence on finite-time
disentanglement and in some cases prevents its appearance. At near-field inter
atomic distances well localized atoms, with maximally one atom being initially
excited, may suffer disentanglement at a single finite time or even at a series
of equidistant finite times, depending on their mean inter atomic distance and
their initial electronic preparation.Comment: 13 pages, 1 figure, submitted to Physical Review on august 2
Sudden Death of Entanglement of Two Jaynes-Cummings Atoms
We investigate entanglement dynamics of two isolated atoms, each in its own
Jaynes-Cummings cavity. We show analytically that initial entanglement has an
interesting subsequent time evolution, including the so-called sudden death
effect.Comment: 3 pages, 3 figure
Two interacting atoms in a cavity: exact solutions, entanglement and decoherence
We address the problem of two interacting atoms of different species inside a
cavity and find the explicit solutions of the corresponding eigenvalues and
eigenfunctions using a new invariant. This model encompasses various commonly
used models. By way of example we obtain closed expressions for concurrence and
purity as a function of time for the case where the cavity is prepared in a
number state. We discuss the behaviour of these quantities and and their
relative behaviour in the concurrence-purity plane.Comment: 10 pages, 3 figure
Speed of disentanglement in multi-qubit systems under depolarizing channel
We investigate the speed of disentanglement in the multiqubit systems under
the local depolarizing channel, in which each qubit is independently coupled to
the environment. We focus on the bipartition entanglement between one qubit and
the remaining qubits constituting the system, which is measured by the
negativity. For the two-qubit system, the speed for the pure state completely
depends on its entanglement. The upper and lower bounds of the speed for
arbitrary two-qubit states, and the necessary conditions for a state achieving
them, are obtained. For the three-qubit system, we study the speed for pure
states, whose entanglement properties can be completely described by five
local-unitary-transformation invariants. An analytical expression of the
relation between the speed and the invariants is derived. The speed is enhanced
by the the three-tangle which is the entanglement among the three qubits, but
reduced by the the two-qubit correlations outside of the concurrence. The decay
of the negativity can be restrained by the other two negativity with the
coequal sense. The unbalance between two qubits can reduce speed of
disentanglement of the remaining qubit in the system, even can retrieve the
entanglement partially. For the k-qubit systems in an arbitrary superposition
of GHZ state and W state, the speed depends almost entirely on the amount of
the negativity when k increases to five or six. An alternative quantitative
definition for the robustness of entanglement is presented based on the speed
of disentanglement, with comparison to the widely studied robustness measured
by the critical amount of noise parameter where the entanglement vanishes. In
the limit of large number of particles, the alternative robustness of the
GHZ-type states is inversely proportional to k, and the one of the W states
approaches 1/\sqrt{k}.Comment: 14 pages, 5 figures. to appear in Annals of Physic