119 research outputs found
Connection between dynamics and thermodynamics of liquids on the melting line
The dynamics of a large number of liquids and polymers exhibit scaling
properties characteristic of a simple repulsive inverse power law (IPL)
potential, most notably the superpositioning of relaxation data as a function
of the variable TV{\gamma}, where T is temperature, V the specific volume, and
{\gamma} a material constant. A related scaling law, TmVm{\Gamma}, with the
same exponent {\Gamma}={\gamma}, links the melting temperature Tm and volume Vm
of the model IPL liquid; liquid dynamics is then invariant at the melting
point. Motivated by a similar invariance of dynamics experimentally observed at
transitions of liquid crystals, we determine dynamic and melting point scaling
exponents {\gamma} and {\Gamma} for a large number of non-associating liquids.
Rigid, spherical molecules containing no polar bonds have {\Gamma}={\gamma};
consequently, the reduced relaxation time, viscosity and diffusion coefficient
are each constant along the melting line. For other liquids {\gamma}>{\Gamma}
always; i.e., the dynamics is more sensitive to volume than is the melting
point, and for these liquids the dynamics at the melting point slows down with
increasing Tm (that is, increasing pressure).Comment: 20 pages, 8 figures, 1 tabl
An operational framework for nonlocality
Due to the importance of entanglement for quantum information purposes, a
framework has been developed for its characterization and quantification as a
resource based on the following operational principle: entanglement among
parties cannot be created by local operations and classical communication, even
when parties collaborate. More recently, nonlocality has been identified
as another resource, alternative to entanglement and necessary for
device-independent quantum information protocols. We introduce an operational
framework for nonlocality based on a similar principle: nonlocality among
parties cannot be created by local operations and allowed classical
communication even when parties collaborate. We then show that the
standard definition of multipartite nonlocality, due to Svetlichny, is
inconsistent with this operational approach: according to it, genuine
tripartite nonlocality could be created by two collaborating parties. We
finally discuss alternative definitions for which consistency is recovered
Nonlocality in sequential correlation scenarios
As first shown by Popescu [S. Popescu, Phys. Rev. Lett. 74, 2619 (1995)],
some quantum states only reveal their nonlocality when subjected to a sequence
of measurements while giving rise to local correlations in standard Bell tests.
Motivated by this manifestation of "hidden nonlocality" we set out to develop a
general framework for the study of nonlocality when sequences of measurements
are performed. Similar to [R. Gallego et al., Phys. Rev. Lett. 109, 070401
(2013)] our approach is operational, i.e. the task is to identify the set of
allowed operations in sequential correlation scenarios and define nonlocality
as the resource that cannot be created by these operations. This leads to a
characterisation of sequential nonlocality that contains as particular cases
standard nonlocality and hidden nonlocality.Comment: 13 pages, 3 figure
Die Verschlüsselung der Korrespondenz des kaiserlichen Residenzen in Konstantinopel, Alexander von Greiffenklau zu Vollrads (1643-48)
This paper analyses the encryption of the correspondence of the imperial resident ambassador in Constantinople, Alexander von Greiffenklau zu Vollrads (1643–48). For early modern diplomats, information security was a vital necessity because intercepted letters could negatively affect the course of negotiations. For encryption purposes, Habsburg diplomats used a method where numbers were substituted for letters, vowels or words. Greiffenklau’s encryption key stands out as comparatively simple, and would have hardly withstood a serious decryption attempt. He only partially encrypted his letters, but two types of information were encrypted particularly often: reports concerning the peace between the Ottomans and the Habsburgs and accounts regarding the Ottoman Empire’s internal affairs
Quantum correlations require multipartite information principles
Identifying which correlations among distant observers are possible within
our current description of Nature, based on quantum mechanics, is a fundamental
problem in Physics. Recently, information concepts have been proposed as the
key ingredient to characterize the set of quantum correlations. Novel
information principles, such as, information causality or non-trivial
communication complexity, have been introduced in this context and successfully
applied to some concrete scenarios. We show in this work a fundamental
limitation of this approach: no principle based on bipartite information
concepts is able to single out the set of quantum correlations for an arbitrary
number of parties. Our results reflect the intricate structure of quantum
correlations and imply that new and intrinsically multipartite information
concepts are needed for their full understanding.Comment: Appendix adde
Useful multipartite correlations from useless reduced states
Understanding what can be inferred about a multi-particle quantum system from
only the knowledge of its subparts is a highly non-trivial task. Clearly, if
the global system doesn't contain any information resource, nor do its
subparts. However, is the converse also true? We show that the answer to is
negative. We provide three two-qubit states that are non-entangled, but such
that any three-qubit state compatible with them is entangled. Entanglement can
thus be deduced from the mere observation of separable reduced states. We
extend this finding to correlations and provide local marginal correlations
that are only compatible with global genuinely tripartite non-local
correlations.Comment: Changed order of presentation, references to previous work of G.Toth,
O. G\"uhne, and co-workers adde
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