2,424 research outputs found
The quantum dynamic capacity formula of a quantum channel
The dynamic capacity theorem characterizes the reliable communication rates
of a quantum channel when combined with the noiseless resources of classical
communication, quantum communication, and entanglement. In prior work, we
proved the converse part of this theorem by making contact with many previous
results in the quantum Shannon theory literature. In this work, we prove the
theorem with an "ab initio" approach, using only the most basic tools in the
quantum information theorist's toolkit: the Alicki-Fannes' inequality, the
chain rule for quantum mutual information, elementary properties of quantum
entropy, and the quantum data processing inequality. The result is a simplified
proof of the theorem that should be more accessible to those unfamiliar with
the quantum Shannon theory literature. We also demonstrate that the "quantum
dynamic capacity formula" characterizes the Pareto optimal trade-off surface
for the full dynamic capacity region. Additivity of this formula simplifies the
computation of the trade-off surface, and we prove that its additivity holds
for the quantum Hadamard channels and the quantum erasure channel. We then
determine exact expressions for and plot the dynamic capacity region of the
quantum dephasing channel, an example from the Hadamard class, and the quantum
erasure channel.Comment: 24 pages, 3 figures; v2 has improved structure and minor corrections;
v3 has correction regarding the optimizatio
Entanglement measures and approximate quantum error correction
It is shown that, if the loss of entanglement along a quantum channel is
sufficiently small, then approximate quantum error correction is possible,
thereby generalizing what happens for coherent information. Explicit bounds are
obtained for the entanglement of formation and the distillable entanglement,
and their validity naturally extends to other bipartite entanglement measures
in between. Robustness of derived criteria is analyzed and their tightness
compared. Finally, as a byproduct, we prove a bound quantifying how large the
gap between entanglement of formation and distillable entanglement can be for
any given finite dimensional bipartite system, thus providing a sufficient
condition for distillability in terms of entanglement of formation.Comment: 7 pages, two-columned revtex4, no figures. v1: Deeply revised and
extended version: different entanglement measures are separately considered,
references are added, and some remarks are stressed. v2: Added a sufficient
condition for distillability in terms of entanglement of formation; published
versio
A dynamical model for quantum memory channels
A dynamical model for quantum channel is introduced which allows one to pass
continuously from the memoryless case to the case in which memory effects are
present. The quantum and classical communication rates of the model are defined
and explicit expression are provided in some limiting case. In this context we
introduce noise attenuation strategies where part of the signals are sacrificed
to modify the channel environment. The case of qubit channel with phase damping
noise is analyzed in details.Comment: 11 pages, 4 figures; minor correction adde
Comment on "The black hole final state"
Horowitz and Maldacena have suggested that the unitarity of the black hole
S-matrix can be reconciled with Hawking's semiclassical arguments if a
final-state boundary condition is imposed at the spacelike singularity inside
the black hole. We point out that, in this scenario, departures from unitarity
can arise due to interactions between the collapsing body and the infalling
Hawking radiation inside the event horizon. The amount of information lost when
a black hole evaporates depends on the extent to which these interactions are
entangling.Comment: 4 pages, REVTe
Effects of initial-state fluctuations in pbpb and ppb collisions at the cms experiment.
У овој тези предтсављена је систематска анализа нарушења факторизације дугодометних азимуталних дво-честичних корелација...In this thesis systematic studies on factorization breaking of long-range azimuthal twoparticle correlations into a product of single-particle anisotropies are presented, as a function of transverse momentum (pT) and pseudorapidity of both particles, and as a function of the particle multiplicity in PbPb and pPb collisions..
Quantum information can be negative
Given an unknown quantum state distributed over two systems, we determine how
much quantum communication is needed to transfer the full state to one system.
This communication measures the "partial information" one system needs
conditioned on it's prior information. It turns out to be given by an extremely
simple formula, the conditional entropy. In the classical case, partial
information must always be positive, but we find that in the quantum world this
physical quantity can be negative. If the partial information is positive, its
sender needs to communicate this number of quantum bits to the receiver; if it
is negative, the sender and receiver instead gain the corresponding potential
for future quantum communication. We introduce a primitive "quantum state
merging" which optimally transfers partial information. We show how it enables
a systematic understanding of quantum network theory, and discuss several
important applications including distributed compression, multiple access
channels and multipartite assisted entanglement distillation (localizable
entanglement). Negative channel capacities also receive a natural
interpretation
Entanglement transmission and generation under channel uncertainty: Universal quantum channel coding
We determine the optimal rates of universal quantum codes for entanglement
transmission and generation under channel uncertainty. In the simplest scenario
the sender and receiver are provided merely with the information that the
channel they use belongs to a given set of channels, so that they are forced to
use quantum codes that are reliable for the whole set of channels. This is
precisely the quantum analog of the compound channel coding problem. We
determine the entanglement transmission and entanglement-generating capacities
of compound quantum channels and show that they are equal. Moreover, we
investigate two variants of that basic scenario, namely the cases of informed
decoder or informed encoder, and derive corresponding capacity results.Comment: 45 pages, no figures. Section 6.2 rewritten due to an error in
equation (72) of the old version. Added table of contents, added section
'Conclusions and further remarks'. Accepted for publication in
'Communications in Mathematical Physics
Review of Antlions (Insecta: Neuroptera: Myrmeleontidae) in North Macedonia
We present the state of knowledge on the family Myrmeleontidae occurring in North Macedonia based on published records, museum specimens and new samples, and provide a comprehensive species list. North Macedonia represents only 3.9% of the area of the Balkan Peninsula but harbours 19 species belonging to 14 antlion genera, i.e., 61% of the peninsular fauna. We report collection localities, literature records and biological data for each species. Three species, Nemoleon poecilopterus, Neuroleon assimilis and Myrmeleon inconspicuus, are reported for the first time in North Macedonia. The genus Nemoleon Navás is also reported for the first time in the country
Simple test for quantum channel capacity
Basing on states and channels isomorphism we point out that semidefinite
programming can be used as a quick test for nonzero one-way quantum channel
capacity. This can be achieved by search of symmetric extensions of states
isomorphic to a given quantum channel. With this method we provide examples of
quantum channels that can lead to high entanglement transmission but still have
zero one-way capacity, in particular, regions of symmetric extendibility for
isotropic states in arbitrary dimensions are presented. Further we derive {\it
a new entanglement parameter} based on (normalised) relative entropy distance
to the set of states that have symmetric extensions and show explicitly the
symmetric extension of isotropic states being the nearest to singlets in the
set of symmetrically extendible states. The suitable regularisation of the
parameter provides a new upper bound on one-way distillable entanglement.Comment: 6 pages, no figures, RevTeX4. Signifficantly corrected version. Claim
on continuity of channel capacities removed due to flaw in the corresponding
proof. Changes and corrections performed in the part proposing a new upper
bound on one-way distillable etanglement which happens to be not one-way
entanglement monoton
Private quantum decoupling and secure disposal of information
Given a bipartite system, correlations between its subsystems can be
understood as information that each one carries about the other. In order to
give a model-independent description of secure information disposal, we propose
the paradigm of private quantum decoupling, corresponding to locally reducing
correlations in a given bipartite quantum state without transferring them to
the environment. In this framework, the concept of private local randomness
naturally arises as a resource, and total correlations get divided into
eliminable and ineliminable ones. We prove upper and lower bounds on the amount
of ineliminable correlations present in an arbitrary bipartite state, and show
that, in tripartite pure states, ineliminable correlations satisfy a monogamy
constraint, making apparent their quantum nature. A relation with entanglement
theory is provided by showing that ineliminable correlations constitute an
entanglement parameter. In the limit of infinitely many copies of the initial
state provided, we compute the regularized ineliminable correlations to be
measured by the coherent information, which is thus equipped with a new
operational interpretation. In particular, our results imply that two
subsystems can be privately decoupled if their joint state is separable.Comment: Child of 0807.3594 v2: minor changes v3: presentation improved, one
figure added v4: extended version with a lot of discussions and examples v5:
published versio
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