4,525 research outputs found
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
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.
The Stellar IMF in Very Metal-Deficient Gas
In the context of the star formation through the fragmentation of an
extremely metal-deficient protogalactic cloud, the gravitational collapse of
filamentary gas clouds is explored with H and HD chemistry. It is found by
1D hydrodynamical simulations that the cloud evolution is prescribed mainly by
the initial density () and H abundance (). In
particular, it turns out that the evolution of low-density filaments ( cm) bifurcates at a critical H abundance of , beyond which HD cooling overwhelms H
cooling. The numerical results indicate that the stellar IMF is likely to be
double-peaked and deficient in sub-solar mass stars, where the high mass peak
of the IMF is around or , dependently on the initial
density and H abundance. If the gas in protogalactic clouds is photoionized
by UV radiation or shock-heated, the H abundance could exceed
by H reactions. Then, the high
mass peak would be .Comment: 4 pages, 1 figure, proceedings of New Quests in Stellar Astrophysics:
The link between Stars and Cosmology (eds. M. Chavez, A. Bressan, A. Buzzoni
& D. Mayya, to be published by the Kluwer Academic Publishers
Quantifying Genuine Multipartite Correlations and their Pattern Complexity
We propose an information-theoretic framework to quantify multipartite correlations in classical and quantum systems, answering questions such as what is the amount of seven-partite correlations in a given state of ten particles? We identify measures of genuine multipartite correlations, i.e., statistical dependencies that cannot be ascribed to bipartite correlations, satisfying a set of desirable properties. Inspired by ideas developed in complexity science, we then introduce the concept of weaving to classify states that display different correlation patterns, but cannot be distinguished by correlation measures. The weaving of a state is defined as the weighted sum of correlations of every order. Weaving measures are good descriptors of the complexity of correlation structures in multipartite systems
Conditional quantum nonlocality in dimeric and trimeric arrays of organic molecules
Arrays of covalently bound organic molecules possess potential for
light-harvesting and energy transfer applications due to the strong coherent
dipole-dipole coupling between the transition dipole moments of the molecules
involved. Here, we show that such molecular systems, based on
perylene-molecules, can be considered as arrays of qubits that are amenable for
laser-driven quantum coherent control. The perylene monomers exhibit dephasing
times longer than four orders of magnitude a typical gating time, thus allowing
for the execution of a large number of gate operations on the sub-picosecond
timescale. Specifically, we demonstrate quantum logic gates and entanglement in
bipartite (dimer) and tripartite (trimer) systems of perylene-based arrays. In
dimers, naturally entangled states with a tailored degree of entanglement can
be produced. The nonlocality of the molecular trimer entanglement is
demonstrated by testing Mermin's (Bell-like) inequality violation.Comment: 14 pages, 8 figures, comments are welcom
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