35 research outputs found
Sudden Death and Birth of Entanglement Effects for Kerr-Nonlinear Coupler
We analyse the entanglement dynamics in a nonlinear Kerr-like coupler
interacting with external environment. Whenever the reservoir is in a thermal
vacuum state the entanglement (measured by concurrence for a two-qubit system)
exhibits regular oscillations of decreasing amplitude. In contrast, for thermal
reservoirs we can observe dark periods in concurrence oscillations (which can
be called a "sudden death" of the entanglement) and the entanglement rebuild
(which can be named the "sudden birth" of entanglement). We show that these
features can be observed when we deal with 2-qubit system as well as system.Comment: 18 pages including 7 figures. Journal of the Optical Society of
America B - in pres
Quantum and Classical Optics–Emerging Links
Quantum optics and classical optics are linked in ways that are becoming apparent as a result of numerous recent detailed examinations of the relationships that elementary notions of optics have with each other. These elementary notions include interference, polarization, coherence, complementarity and entanglement. All of them are present in both quantum and classical optics. They have historic origins, and at least partly for this reason not all of them have quantitative definitions that are universally accepted. This makes further investigation into their engagement in optics very desirable. We pay particular attention to effects that arise from the mere co-existence of separately identifiable and readily available vector spaces. Exploitation of these vector-space relationships are shown to have unfamiliar theoretical implications and new options for observation. It is our goal to bring emerging quantum–classical links into wider view and to indicate directions in which forthcoming and future work will promote discussion and lead to unified understanding
New features of quantum discord uncovered by q-entropies
The notion of quantum discord introduced by Ollivier and Zurek [Phys. Rev.
Lett 88, 017901 (2001)] (see also Henderson and Vedral [J. Phys. A 34, 6899
(2001)]) has attracted increasing attention, in recent years, as an entropic
quantifier of non-classical features pertaining to the correlations exhibited
by bipartite quantum systems. Here we generalize the notion so as to encompass
power-law q-entropies (that reduce to the standard Shannon entropy in the limit
) and study the concomitant consequences. The ensuing, new
discord-like measures we advance describe aspects of non-classicality that are
different from those associated with the standard quantum discord. A particular
manifestation of this difference concerns a feature related to order. Let
stand for the standard, Shannon-based discord measure and for the one. If two quantum states , are such that , this
order-relation does not remain invariant under a change from to .Comment: 11 pages, 8 figure
Decay of entanglement in coupled, driven systems with bipartite decoherence
We analyze a system of two qubits embedded in two different environments. The
qubits are coupled to each other and driven on-resonance by two external
classical sources. In the secular limit, we obtain exact analytical results for
the evolution of the system for several classes of two-qubit mixed initial
states. For Werner states we show that the decay of entanglement does not
depend on coupling. For other initial states with ``{\sf X}\rq\rq -type density
matrices we find that the sudden death time displays a rich dependence on the
coupling energy and state parameters due to the existence of processes of
delayed sudden birth of entanglement.Comment: 9 pages, 8 figure
Modulated Entanglement Evolution Via Correlated Noises
We study entanglement dynamics in the presence of correlated environmental
noises. Specifically, we investigate the quantum entanglement dynamics of two
spins in the presence of correlated classical white noises, deriving Markov
master equation and obtaining explicit solutions for several interesting
classes of initial states including Bell states and X form density matrices. We
show how entanglement can be enhanced or reduced by the correlation between the
two participating noises.Comment: 9 pages, 4 figures. To be published in Quantum Information
Processing, special issue on Quantum Decoherence and Entanglemen
Predominance of entanglement of formation over quantum discord under quantum channels
We present a study of the behavior of two different figures of merit for
quantum correlations, entanglement of formation and quantum discord, under
quantum channels showing how the former can, counterintuitively, be more
resilient to such environments spoiling effects. By exploiting strict
conservation relations between the two measures and imposing necessary
constraints on the initial conditions we are able to explicitly show this
predominance is related to build-up of the system-environment correlations.Comment: 7 pages, 5 figures, RevTeX
Quantum entanglement and disentanglement of multi-atom systems
We present a review of recent research on quantum entanglement, with special
emphasis on entanglement between single atoms, processing of an encoded
entanglement and its temporary evolution. Analysis based on the density matrix
formalism are described. We give a simple description of the entangling
procedure and explore the role of the environment in creation of entanglement
and in disentanglement of atomic systems. A particular process we will focus on
is spontaneous emission, usually recognized as an irreversible loss of
information and entanglement encoded in the internal states of the system. We
illustrate some certain circumstances where this irreversible process can in
fact induce entanglement between separated systems. We also show how
spontaneous emission reveals a competition between the Bell states of a two
qubit system that leads to the recently discovered "sudden" features in the
temporal evolution of entanglement. An another problem illustrated in details
is a deterministic preparation of atoms and atomic ensembles in long-lived
stationary squeezed states and entangled cluster states. We then determine how
to trigger the evolution of the stable entanglement and also address the issue
of a steered evolution of entanglement between desired pairs of qubits that can
be achieved simply by varying the parameters of a given system.Comment: Review articl
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
Finite-time destruction of entanglement and non-locality by environmental influences
Entanglement and non-locality are non-classical global characteristics of
quantum states important to the foundations of quantum mechanics. Recent
investigations have shown that environmental noise, even when it is entirely
local in influence, can destroy both of these properties in finite time despite
giving rise to full quantum state decoherence only in the infinite time limit.
These investigations, which have been carried out in a range of theoretical and
experimental situations, are reviewed here.Comment: 27 pages, 6 figures, review article to appear in Foundations of
Physic