301 research outputs found
Total correlations as fully additive entanglement monotones
We generalize the strategy presented in Refs. [1, 2], and propose general
conditions for a measure of total correlations to be an entanglement monotone
using its pure (and mixed) convex-roof extension. In so doing, we derive
crucial theorems and propose a concrete candidate for a total correlations
measure which is a fully additive entanglement monotone.Comment: 8 pages, 3 figures. Title changed, new result
Non-equilibrium entanglement in a driven Dicke model
We study the entanglement dynamics in the externally-driven single-mode Dicke
model in the thermodynamic limit, when the field is in resonance with the
atoms. We compute the correlations in the atoms-field ground state by means of
the density operator that represents the pure state of the universe and the
reduced density operator for the atoms, which results from taking the partial
trace over the field coordinates. As a measure of bipartite entanglement, we
calculate the linear entropy, from which we analyze the entanglement dynamics.
In particular, we found a strong relation between the stability of the
dynamical parameters and the reported entanglement.Comment: Contribution to the SLAFES XIX. This version to appear in J. Phys.:
Conference Serie
Extracting Information from Qubit-Environment Correlations
Most works on open quantum systems generally focus on the reduced physical
system by tracing out the environment degrees of freedom. Here we show that the
qubit distributions with the environment are essential for a thorough analysis,
and demonstrate that the way that quantum correlations are distributed in a
quantum register is constrained by the way in which each subsystem gets
correlated with the environment. For a two-qubit system coupled to a common
dissipative environment , we show how to optimise interqubit
correlations and entanglement via a quantification of the qubit-environment
information flow, in a process that, perhaps surprisingly, does not rely on the
knowledge of the state of the environment. To illustrate our findings, we
consider an optically-driven bipartite interacting qubit system under the
action of . By tailoring the light-matter interaction, a
relationship between the qubits early stage disentanglement and the
qubit-environment entanglement distribution is found. We also show that, under
suitable initial conditions, the qubits energy asymmetry allows the
identification of physical scenarios whereby qubit-qubit entanglement minima
coincide with the extrema of the and entanglement
oscillations.Comment: 4 figures, 9 page
Anticrossings in Foerster Coupled Quantum Dots
We consider two coupled generic quantum dots, each modelled by a simple
potential which allows the derivation of an analytical expression for the
inter-dot Foerster coupling, in the dipole-dipole approximation. We investigate
the energy level behaviour of this coupled two-dot system under the influence
of an external applied electric field and predict the presence of anticrossings
in the optical spectra due to the Foerster interaction.Comment: 13 pages, 7 figures. Published version. Substantially revised, new
sections on decay rates, absorption spectra, and tunnelin
Correlations in optically-controlled quantum emitters
We address the problem of optically controlling and quantifying the
dissipative dynamics of quantum and classical correlations in a set-up of
individual quantum emitters under external laser excitation. We show that both
types of correlations, the former measured by the quantum discord, are present
in the system's evolution even though the emitters may exhibit an early stage
disentanglement. In the absence of external laser pumping,we demonstrate
analytically, for a set of suitable initial states, that there is an entropy
bound for which quantum discord and entanglement of the emitters are always
greater than classical correlations, thus disproving an early conjecture that
classical correlations are greater than quantum correlations. Furthermore, we
show that quantum correlations can also be greater than classical correlations
when the system is driven by a laser field. For scenarios where the emitters'
quantum correlations are below their classical counterparts, an optimization of
the evolution of the quantum correlations can be carried out by appropriately
tailoring the amplitude of the laser field and the emitters' dipole-dipole
interaction. We stress the importance of using the entanglement of formation,
rather than the concurrence, as the entanglement measure, since the latter can
grow beyond the total correlations and thus give incorrect results on the
actual system's degree of entanglement.Comment: 11 pages, 10 figures, this version contains minor modifications; to
appear in Phys. Rev.
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