3,742 research outputs found
Violation of Bell inequalities by photons more than 10 km apart
A Franson-type test of Bell inequalities by photons 10.9 km apart is
presented. Energy-time entangled photon-pairs are measured using two-channel
analyzers, leading to a violation of the inequalities by 16 standard deviations
without subtracting accidental coincidences. Subtracting them, a 2-photon
interference visibility of 95.5% is observed, demonstrating that distances up
to 10 km have no significant effect on entanglement. This sets quantum
cryptography with photon pairs as a practical competitor to the schemes based
on weak pulses.Comment: 4 pages, REVTeX, 2 postscript figures include
From quantum-codemaking to quantum code-breaking
This is a semi-popular overview of quantum entanglement as an important
physical resource in the field of data security and quantum computing. After a
brief outline of entanglement's key role in philosophical debates about the
meaning of quantum mechanics I describe its current impact on both cryptography
and cryptanalysis. The paper is based on the lecture given at the conference
"Geometric Issues in the Foundations of Science" (Oxford, June 1996) in honor
of Roger Penrose.Comment: 21 pages, LaTeX2e, psfig, multi3.cls, 1 eps figur
Limits to Non-Malleability
There have been many successes in constructing explicit non-malleable codes for various classes of tampering functions in recent years, and strong existential results are also known. In this work we ask the following question:
When can we rule out the existence of a non-malleable code for a tampering class ??
First, we start with some classes where positive results are well-known, and show that when these classes are extended in a natural way, non-malleable codes are no longer possible. Specifically, we show that no non-malleable codes exist for any of the following tampering classes:
- Functions that change d/2 symbols, where d is the distance of the code;
- Functions where each input symbol affects only a single output symbol;
- Functions where each of the n output bits is a function of n-log n input bits.
Furthermore, we rule out constructions of non-malleable codes for certain classes ? via reductions to the assumption that a distributional problem is hard for ?, that make black-box use of the tampering functions in the proof. In particular, this yields concrete obstacles for the construction of efficient codes for NC, even assuming average-case variants of P ? NC
Distillation of Multi-Party Non-Locality With and Without Partial Communication
Non-local correlations are one of the most fascinating consequences of
quantum physics from the point of view of information: Such correlations,
although not allowing for signaling, are unexplainable by pre-shared
information. The correlations have applications in cryptography, communication
complexity, and sit at the very heart of many attempts of understanding quantum
theory -- and its limits -- better in terms of classical information. In these
contexts, the question is crucial whether such correlations can be distilled,
i.e., whether weak correlations can be used for generating (a smaller amount
of) stronger. Whereas the question has been studied quite extensively for
bipartite correlations (yielding both pessimistic and optimistic results), only
little is known in the multi-partite case. We show that a natural
generalization of the well-known Popsecu-Rohrlich box can be distilled, by an
adaptive protocol, to the algebraic maximum. We use this result further to show
that a much bigger class of correlations, including all purely three-partite
correlations, can be distilled from arbitrarily weak to maximal strength with
partial communication, i.e., using only a subset of the channels required for
the creation of the same correlation from scratch. In other words, we show that
arbitrarily weak non-local correlations can have a "communication value" in the
context of the generation of maximal non-locality.Comment: 5 pages, 3 figure
Long-distance Bell-type tests using energy-time entangled photons
Long-distance Bell-type experiments are presented. The different experimental
challenges and their solutions in order to maintain the strong quantum
correlations between energy-time entangled photons over more than 10 km are
reported and the results analyzed from the point of view of tests of
fundamental physics as well as from the more applied side of quantum
communication, specially quantum key distribution. Tests using more than one
analyzer on each side are also presented.Comment: 22 pages including 7 figures and 5 table
Long-distance Bell-type tests using energy-time entangled photons
Long-distance Bell-type experiments are presented. The different experimental
challenges and their solutions in order to maintain the strong quantum
correlations between energy-time entangled photons over more than 10 km are
reported and the results analyzed from the point of view of tests of
fundamental physics as well as from the more applied side of quantum
communication, specially quantum key distribution. Tests using more than one
analyzer on each side are also presented.Comment: 22 pages including 7 figures and 5 table
Faster tuple lattice sieving using spherical locality-sensitive filters
To overcome the large memory requirement of classical lattice sieving
algorithms for solving hard lattice problems, Bai-Laarhoven-Stehl\'{e} [ANTS
2016] studied tuple lattice sieving, where tuples instead of pairs of lattice
vectors are combined to form shorter vectors. Herold-Kirshanova [PKC 2017]
recently improved upon their results for arbitrary tuple sizes, for example
showing that a triple sieve can solve the shortest vector problem (SVP) in
dimension in time , using a technique similar to
locality-sensitive hashing for finding nearest neighbors.
In this work, we generalize the spherical locality-sensitive filters of
Becker-Ducas-Gama-Laarhoven [SODA 2016] to obtain space-time tradeoffs for near
neighbor searching on dense data sets, and we apply these techniques to tuple
lattice sieving to obtain even better time complexities. For instance, our
triple sieve heuristically solves SVP in time . For
practical sieves based on Micciancio-Voulgaris' GaussSieve [SODA 2010], this
shows that a triple sieve uses less space and less time than the current best
near-linear space double sieve.Comment: 12 pages + references, 2 figures. Subsumed/merged into Cryptology
ePrint Archive 2017/228, available at https://ia.cr/2017/122
Complete experimental toolbox for alignment-free quantum communication
Quantum communication employs the counter-intuitive features of quantum
physics to perform tasks that are im- possible in the classical world. It is
crucial for testing the foundations of quantum theory and promises to rev-
olutionize our information and communication technolo- gies. However, for two
or more parties to execute even the simplest quantum transmission, they must
establish, and maintain, a shared reference frame. This introduces a
considerable overhead in communication resources, par- ticularly if the parties
are in motion or rotating relative to each other. We experimentally demonstrate
how to circumvent this problem with the efficient transmission of quantum
information encoded in rotationally invariant states of single photons. By
developing a complete toolbox for the efficient encoding and decoding of
quantum infor- mation in such photonic qubits, we demonstrate the fea- sibility
of alignment-free quantum key-distribution, and perform a proof-of-principle
alignment-free entanglement distribution and violation of a Bell inequality.
Our scheme should find applications in fundamental tests of quantum mechanics
and satellite-based quantum communication.Comment: Main manuscript: 7 pages, 3 figures; Supplementary Information: 7
pages, 3 figure
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