102 research outputs found
On Quantum Advantage in Information Theoretic Single-Server PIR
In (single-server) Private Information Retrieval (PIR), a server holds a
large database of size , and a client holds an index and
wishes to retrieve without revealing to the server. It is well
known that information theoretic privacy even against an `honest but curious'
server requires communication complexity. This is true even if
quantum communication is allowed and is due to the ability of such an
adversarial server to execute the protocol on a superposition of databases
instead of on a specific database (`input purification attack'). Nevertheless,
there have been some proposals of protocols that achieve sub-linear
communication and appear to provide some notion of privacy. Most notably, a
protocol due to Le Gall (ToC 2012) with communication complexity ,
and a protocol by Kerenidis et al. (QIC 2016) with communication complexity
, and shared entanglement.
We show that, in a sense, input purification is the only potent adversarial
strategy, and protocols such as the two protocols above are secure in a
restricted variant of the quantum honest but curious (a.k.a specious) model.
More explicitly, we propose a restricted privacy notion called \emph{anchored
privacy}, where the adversary is forced to execute on a classical database
(i.e. the execution is anchored to a classical database). We show that for
measurement-free protocols, anchored security against honest adversarial
servers implies anchored privacy even against specious adversaries.
Finally, we prove that even with (unlimited) pre-shared entanglement it is
impossible to achieve security in the standard specious model with sub-linear
communication, thus further substantiating the necessity of our relaxation.
This lower bound may be of independent interest (in particular recalling that
PIR is a special case of Fully Homomorphic Encryption)
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
DFTB+, a software package for efficient approximate density functional theory based atomistic simulations
DFTB+ is a versatile community developed open source software package offering fast and efficient methods for carrying out atomistic quantum mechanical simulations. By implementing various methods approximating density functional theory (DFT), such as the density functional based tight binding (DFTB) and the extended tight binding method, it enables simulations of large systems and long timescales with reasonable accuracy while being considerably faster for typical simulations than the respective ab initio methods. Based on the DFTB framework, it additionally offers approximated versions of various DFT extensions including hybrid functionals, time dependent formalism for treating excited systems, electron transport using non-equilibrium Green's functions, and many more. DFTB+ can be used as a user-friendly standalone application in addition to being embedded into other software packages as a library or acting as a calculation-server accessed by socket communication. We give an overview of the recently developed capabilities of the DFTB+ code, demonstrating with a few use case examples, discuss the strengths and weaknesses of the various features, and also discuss on-going developments and possible future perspectives
Maternal and fetal blood lipid concentrations during pregnancy differ by maternal body mass index: findings from the ROLO study
Helicity-dependent cross sections for the photoproduction of pairs from nucleons
The double-polarization observable and helicity-dependent cross sections
, have been measured for the photoproduction of
pairs off quasi-free protons and neutrons at the Mainz MAMI accelerator
with the Crystal Ball/TAPS setup. A circularly polarized photon beam was
produced by bremsstrahlung from longitudinally polarized electrons and impinged
on a longitudinally polarized deuterated butanol target. The reaction products
were detected with an almost covering calorimeter. The results reveal
for the first time the helicity- and isospin-dependent structure of the reaction. They are compared to predictions from
reaction models in view of nucleon resonance contributions and also to a refit
of one model that predicted results for the proton and for the neutron target.
The comparison of the prediction and the refit demonstrate the large impact of
the new data.Comment: Submitted to Phys. Rev. Let
Modellierungskonzepte der Synergetik und der Theorie der Selbstorganisation
Mnay models situated in the current research landscape of modelling and
simulating social processes have roots in physics. This is visible in the name
of specialties as Econophysics or Sociophysics. This chapter describes the
history of knowledge transfer from physics, in particular physics of
self-organization and evolution, to the social sciences. We discuss why
physicists felt called to describe social processes. Across models and
simulations the question how to explain the emergence of something new is the
most intriguing one. We present one model approach to this problem and
introduce a game -- Evolino -- inviting a larger audience to get acquainted
with abstract evolution-theory approaches to describe the quest for new ideas.Comment: In German, extended first version, final version Ebeling, W., &
Scharnhorst, A. (2015). Modellierungskonzepte der Synergetik und der Theorie
der Selbstorganisation. In N. Braun & N. J. Saam (Eds.), Handbuch
Modellbildung und Simulation in den Sozialwissenschaften (pp. 419--452).
Wiesbaden: Springer Fachmedien Wiesbaden. doi:10.1007/978-3-658-01164-2 (in
German
128 EFFECT OF PERIFOLLICULAR BLOOD FLOW ON THE QUALITY OF OOCYTES COLLECTED DURING REPEATED OPU SESSIONS
315 USE OF PERIFOLLICULAR BLOOD FLOW TO PREDICT THE DEVELOPMENTAL COMPETENCE OF BOVINE CUMULUS-OOCYTE COMPLEXES COLLECTED DURING REPEATED OVUM PICKUP SESSIONS ONCE OR TWICE WEEKLY
313 EVALUATION OF COLOR DOPPLER ULTRASONOGRAPHY OF THE PERIFOLLICULAR BLOOD FLOW TO PREDICT THE DEVELOPMENTAL COMPETENCE OF BOVINE CUMULUS - OOCYTE COMPLEXES COLLECTED DURING REPEATED OVUM PICK-UP SESSIONS
- …