618 research outputs found
Locking classical information
It is known that the maximum classical mutual information that can be
achieved between measurements on a pair of quantum systems can drastically
underestimate the quantum mutual information between those systems. In this
article, we quantify this distinction between classical and quantum information
by demonstrating that after removing a logarithmic-sized quantum system from
one half of a pair of perfectly correlated bitstrings, even the most sensitive
pair of measurements might only yield outcomes essentially independent of each
other. This effect is a form of information locking but the definition we use
is strictly stronger than those used previously. Moreover, we find that this
property is generic, in the sense that it occurs when removing a random
subsystem. As such, the effect might be relevant to statistical mechanics or
black hole physics. Previous work on information locking had always assumed a
uniform message. In this article, we assume only a min-entropy bound on the
message and also explore the effect of entanglement. We find that classical
information is strongly locked almost until it can be completely decoded. As a
cryptographic application of these results, we exhibit a quantum key
distribution protocol that is "secure" if the eavesdropper's information about
the secret key is measured using the accessible information but in which
leakage of even a logarithmic number of key bits compromises the secrecy of all
the others.Comment: 32 pages, 2 figure
Dilemma that cannot be resolved by biased quantum coin flipping
We show that a biased quantum coin flip (QCF) cannot provide the performance
of a black-boxed biased coin flip, if it satisfies some fidelity conditions.
Although such a QCF satisfies the security conditions of a biased coin flip, it
does not realize the ideal functionality, and therefore, does not fulfill the
demands for universally composable security. Moreover, through a comparison
within a small restricted bias range, we show that an arbitrary QCF is
distinguishable from a black-boxed coin flip unless it is unbiased on both
sides of parties against insensitive cheating. We also point out the difficulty
in developing cheat-sensitive quantum bit commitment in terms of the
uncomposability of a QCF.Comment: 5 pages and 1 figure. Accepted versio
Unconditional Security of Single-Photon Differential Phase Shift Quantum Key Distribution
In this Letter, we prove the unconditional security of single-photon
differential phase shift quantum key distribution (DPS-QKD) protocol, based on
the conversion to an equivalent entanglement-based protocol. We estimate the
upper bound of the phase error rate from the bit error rate, and show that
DPS-QKD can generate unconditionally secure key when the bit error rate is not
greater than 4.12%. This proof is the first step to the unconditional security
proof of coherent state DPS-QKD.Comment: 5 pages, 2 figures; shorten the length, improve clarity, and correct
typos; accepted for publication in Physical Review Letter
Quantum cryptography with finite resources: unconditional security bound for discrete-variable protocols with one-way post-processing
We derive a bound for the security of QKD with finite resources under one-way
post-processing, based on a definition of security that is composable and has
an operational meaning. While our proof relies on the assumption of collective
attacks, unconditional security follows immediately for standard protocols like
Bennett-Brassard 1984 and six-states. For single-qubit implementations of such
protocols, we find that the secret key rate becomes positive when at least
N\sim 10^5 signals are exchanged and processed. For any other discrete-variable
protocol, unconditional security can be obtained using the exponential de
Finetti theorem, but the additional overhead leads to very pessimistic
estimates
Optimal ratio between phase basis and bit basis in QKD
In the original BB84 protocol, the bit basis and the phase basis are used
with equal probability. Lo et al (J. of Cryptology, 18, 133-165 (2005))
proposed to modify the ratio between the two bases by increasing the final key
generation rate. However, the optimum ratio has not been derived. In this
letter, in order to examine this problem, the ratio between the two bases is
optimized for exponential constraints given Eve's information
distinguishability and the final error probability
Universally Composable Quantum Multi-Party Computation
The Universal Composability model (UC) by Canetti (FOCS 2001) allows for
secure composition of arbitrary protocols. We present a quantum version of the
UC model which enjoys the same compositionality guarantees. We prove that in
this model statistically secure oblivious transfer protocols can be constructed
from commitments. Furthermore, we show that every statistically classically UC
secure protocol is also statistically quantum UC secure. Such implications are
not known for other quantum security definitions. As a corollary, we get that
quantum UC secure protocols for general multi-party computation can be
constructed from commitments
Multipartite entanglement verification resistant against dishonest parties
Future quantum information networks will likely consist of quantum and
classical agents, who have the ability to communicate in a variety of ways with
trusted and untrusted parties and securely delegate computational tasks to
untrusted large-scale quantum computing servers. Multipartite quantum
entanglement is a fundamental resource for such a network and hence it is
imperative to study the possibility of verifying a multipartite entanglement
source in a way that is efficient and provides strong guarantees even in the
presence of multiple dishonest parties. In this work, we show how an agent of a
quantum network can perform a distributed verification of a multipartite
entangled source with minimal resources, which is, nevertheless, resistant
against any number of dishonest parties. Moreover, we provide a tight tradeoff
between the level of security and the distance between the state produced by
the source and the ideal maximally entangled state. Last, by adding the
resource of a trusted common random source, we can further provide security
guarantees for all honest parties in the quantum network simultaneously.Comment: The statement of Theorem 2 has been revised and a new proof is given.
Other results unchange
Reduction of Soil-Borne Plant Pathogens Using Lime and Ammonia Evolved from Broiler Litter
In laboratory and micro-plots simulations and in a commercial greenhouse, soil ammonia (NH3) and pH were manipulated as means to control soil-borne fungal pathogens and nematodes. Soil ammonification capacity was increased by applying low C/N ratio broiler litter at 1–8% (w/w). Soil pH was increased using lime at 0.5–1% (w/w). This reduced fungi (Fusarium oxysporum f. sp. dianthi and Sclerotium rolfsii) and root-knot nematode (Meloidogyne javanica) in lab tests below detection. In a commercial greenhouse, broiler litter (25 Mg ha−1) and lime (12.5 Mg ha−1) addition to soil in combination with solarization significantly reduced M. javanica induced root galling of tomato test plants from 47% in the control plots (solarization only) to 7% in treated plots. Root galling index of pepper plants, measured 178 days after planting in the treated and control plots, were 0.8 and 1.5, respectively, which was statistically significantly different. However, the numbers of nematode juveniles in the root zone soil counted 83 and 127 days after pepper planting were not significantly different between treatments. Pepper fruit yield was not different between treatments. Soil disinfection and curing was completed within one month, and by the time of bell-pepper planting the pH and ammonia values were normal
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