501 research outputs found
Entanglement of pure states for a single copy
An optimal local conversion strategy between any two pure states of a
bipartite system is presented. It is optimal in that the probability of success
is the largest achievable if the parties which share the system, and which can
communicate classically, are only allowed to act locally on it. The study of
optimal local conversions sheds some light on the entanglement of a single copy
of a pure state. We propose a quantification of such an entanglement by means
of a finite minimal set of new measures from which the optimal probability of
conversion follows.Comment: Revtex, 4 pages, no figures. Minor changes. Appendix remove
Dynamic entanglement in oscillating molecules and potential biological implications
We demonstrate that entanglement can persistently recur in an oscillating
two-spin molecule that is coupled to a hot and noisy environment, in which no
static entanglement can survive. The system represents a non-equilibrium
quantum system which, driven through the oscillatory motion, is prevented from
reaching its (separable) thermal equilibrium state. Environmental noise,
together with the driven motion, plays a constructive role by periodically
resetting the system, even though it will destroy entanglement as usual. As a
building block, the present simple mechanism supports the perspective that
entanglement can exist also in systems which are exposed to a hot environment
and to high levels of de-coherence, which we expect e.g. for biological
systems. Our results furthermore suggest that entanglement plays a role in the
heat exchange between molecular machines and environment. Experimental
simulation of our model with trapped ions is within reach of the current
state-of-the-art quantum technologies.Comment: Extended version, including supplementary information. 9 pages, 8
figure
Classical communication and non-classical fidelity of quantum teleportation
In quantum teleportation, the role of entanglement has been much discussed.
It is known that entanglement is necessary for achieving non-classical
teleportation fidelity. Here we focus on the amount of classical communication
that is necessary to obtain non-classical fidelity in teleportation. We
quantify the amount of classical communication that is sufficient for achieving
non-classical fidelity for two independent 1-bit and single 2-bits noisy
classical channels. It is shown that on average 0.208 bits of classical
communication is sufficient to get non-classical fidelity. We also find the
necessary amount of classical communication in case of isotropic
transformation. Finally we study how the amount of sufficient classical
communication increases with weakening of entanglement used in the
teleportation process.Comment: Accepted in Quantum Info. Proces
Biomass and biological fuels
The analysis of results obtained at national and
international level on the utilization of renewable energy sources pointed
out the opportunity of over-passing the energy crisis by the orientation of
world economy to produce energy by the help of biomass. The high plant
mass volume present in the world could compensate the relatively low
output of light energy conversion through photosynthesis. The climatic
conditions from Romania favourable to plant growing with high capacity of
biomass multiplication, as well as farming by-product, animal dejections,
domestic garbage, can ensure the biogas necessary to cover a great
percentage of the energy necessary for animal breeding farms or heating
dwellings
Diminution in environment pollution by revaluating wastes and crop residues
The paper assesses the amount of by-products from crops obtained every year
in Romania (about 20,637,000 t), pointing out the opportunity of a more economic revaluation
of these produces and of pollution diminution. Cereals straw (about 5 million t each year)
could be used as raw material in the industry of celluloses. Straw residues, maize stalks, marc,
domestic wastes, etc. could be changed into compost, which is used as crop fertilizer.
Sunflower heads (774,000 t each year) and husks (227,000 t each year) represent a source for
producing food vegetable jelly and furfural. Grain legumes stalks (130,000 t), together with
218,000 t leaves and necks, resulted from sugar beet processing, could be used for animal
feeding. Oil is extracted from apricot, sweet cherry, peach, plum, and grape stones (about
87,000 t each year), as well as from tomato seeds
On the elliptical flow in asymmetric collisions and nuclear equation of state
We here present the results of elliptical flow for the collision of different
asymmetric nuclei (10Ne20 +13 Al27, 18Ar40 +21 Sc45, 30Zn64 +28 Ni58, 36Kr86
+41 Nb93) by using the Quantum Molecular Dynamics (QMD) model. General features
of elliptical flow are investigated with the help of theoretical simulations.
The simulations are performed at different beam energies between 40 and 105
MeV/nucleon. A significant change can be seen from in-plane to out-of-plane
elliptical flow of different fragments with incident energy. A comparison with
experimental data is also made. Further, we predict, for the first time that,
elliptical flow for different kind of fragments follow power law dependence ?
C(Atot)? for asymmetric systems
Information-theoretic aspects of quantum inseparability of mixed states
Information-theoretic aspects of quantum inseparability of mixed states are
investigated in terms of the -entropy inequalities and teleportation
fidelity. Inseparability of mixed states is defined and a complete
characterization of the inseparable systems with maximally
disordered subsystems is presented within the Hilbert-Schmidt space formalism.
A connection between teleportation and negative conditional -entropy is
also emphasized.Comment: Revtex, 19 pages, to appear in Phys. Rev. A, vol. 54; one postscript
figure available at request from [email protected]
Fundamental limitations for quantum and nano thermodynamics
The relationship between thermodynamics and statistical physics is valid in
the thermodynamic limit - when the number of particles becomes very large.
Here, we study thermodynamics in the opposite regime - at both the nano scale,
and when quantum effects become important. Applying results from quantum
information theory we construct a theory of thermodynamics in these limits. We
derive general criteria for thermodynamical state transformations, and as
special cases, find two free energies: one that quantifies the
deterministically extractable work from a small system in contact with a heat
bath, and the other that quantifies the reverse process. We find that there are
fundamental limitations on work extraction from nonequilibrium states, owing to
finite size effects and quantum coherences. This implies that thermodynamical
transitions are generically irreversible at this scale. As one application of
these methods, we analyse the efficiency of small heat engines and find that
they are irreversible during the adiabatic stages of the cycle.Comment: Final, published versio
Bell Correlations and the Common Future
Reichenbach's principle states that in a causal structure, correlations of
classical information can stem from a common cause in the common past or a
direct influence from one of the events in correlation to the other. The
difficulty of explaining Bell correlations through a mechanism in that spirit
can be read as questioning either the principle or even its basis: causality.
In the former case, the principle can be replaced by its quantum version,
accepting as a common cause an entangled state, leaving the phenomenon as
mysterious as ever on the classical level (on which, after all, it occurs). If,
more radically, the causal structure is questioned in principle, closed
space-time curves may become possible that, as is argued in the present note,
can give rise to non-local correlations if to-be-correlated pieces of classical
information meet in the common future --- which they need to if the correlation
is to be detected in the first place. The result is a view resembling Brassard
and Raymond-Robichaud's parallel-lives variant of Hermann's and Everett's
relative-state formalism, avoiding "multiple realities."Comment: 8 pages, 5 figure
Dynamics of entanglement between two trapped atoms
We investigate the dynamics of entanglement between two continuous variable
quantum systems. The model system consists of two atoms in a harmonic trap
which are interacting by a simplified s-wave scattering. We show, that the
dynamically created entanglement changes in a steplike manner. Moreover, we
introduce local operators which allow us to violate a Bell-CHSH inequality
adapted to the continuous variable case. The correlations show nonclassical
behavior and almost reach the maximal quantum mechanical value. This is
interesting since the states prepared by this interaction are very different
from any EPR-like state.Comment: 9 page
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