904 research outputs found
Unconditional security at a low cost
By simulating four quantum key distribution (QKD) experiments and analyzing
one decoy-state QKD experiment, we compare two data post-processing schemes
based on security against individual attack by L\"{u}tkenhaus, and
unconditional security analysis by Gottesman-Lo-L\"{u}tkenhaus-Preskill. Our
results show that these two schemes yield close performances. Since the Holy
Grail of QKD is its unconditional security, we conclude that one is better off
considering unconditional security, rather than restricting to individual
attacks.Comment: Accepted by International Conference on Quantum Foundation and
Technology: Frontier and Future 2006 (ICQFT'06
Efficient Heralding of Photonic Qubits with Apllications to Device Independent Quantum Key Distribution
We present an efficient way of heralding photonic qubit signals using linear
optics devices. First we show that one can obtain asymptotically perfect
heralding and unit success probability with growing resources. Second, we show
that even using finite resources, we can improve qualitatively and
quantitatively over earlier heralding results. In the latte r scenario, we can
obtain perfect heralded photonic qubits while maintaining a finite success
probability. We demonstrate the advantage of our heralding scheme by predicting
key rates for device independent quantum key distribution, taking imperfections
of sources and detectors into account
Faint laser quantum key distribution: Eavesdropping exploiting multiphoton pulses
The technological possibilities of a realistic eavesdropper are discussed.
Two eavesdropping strategies taking profit of multiphoton pulses in faint laser
QKD are presented. We conclude that, as long as storage of Qubits is
technically impossible, faint laser QKD is not limited by this security issue,
but mostly by the detector noise.Comment: 7 pages, 6 figure
A simple proof of the unconditional security of quantum key distribution
Quantum key distribution is the most well-known application of quantum
cryptography. Previous proposed proofs of security of quantum key distribution
contain various technical subtleties. Here, a conceptually simpler proof of
security of quantum key distribution is presented. The new insight is the
invariance of the error rate of a teleportation channel: We show that the error
rate of a teleportation channel is independent of the signals being
transmitted. This is because the non-trivial error patterns are permuted under
teleportation. This new insight is combined with the recently proposed quantum
to classical reduction theorem. Our result shows that assuming that Alice and
Bob have fault-tolerant quantum computers, quantum key distribution can be made
unconditionally secure over arbitrarily long distances even against the most
general type of eavesdropping attacks and in the presence of all types of
noises.Comment: 13 pages, extended abstract. Comments will be appreciate
Factors, And Correlates in the Prevalence of Adolescent Delinquency: Do Sports Involvement Non-Sports Involvement Matter?
Child and adolescent involvement in sport activities is widely believed to reduce risky behaviors Sport participation is time consuming and reduces the amount of unsupervised free time duringwhich risky behavior is more likely to occur Additionally sports teams have positive role models and influences encouraging youth to stay out of trouble Although popular belief is that sport participation deters delinquent behavior research findings have been inconsistent Two competing theories supporting the inconsistent findings arethe Social Bonds Theory Hirschi 1969 and the AthleteDelinquentHypothesis Begg Langley Moffit Marshall 1996 The purpose of the current study is to explore delinquency and adolescence utilizing a revised scale on the impact of gender athletic involvement and non-athletic involvement as well as child and teenage correlates with current college student delinquency The implications and limitations are discusse
Quantum Kolmogorov Complexity and Quantum Key Distribution
We discuss the Bennett-Brassard 1984 (BB84) quantum key distribution protocol
in the light of quantum algorithmic information. While Shannon's information
theory needs a probability to define a notion of information, algorithmic
information theory does not need it and can assign a notion of information to
an individual object. The program length necessary to describe an object,
Kolmogorov complexity, plays the most fundamental role in the theory. In the
context of algorithmic information theory, we formulate a security criterion
for the quantum key distribution by using the quantum Kolmogorov complexity
that was recently defined by Vit\'anyi. We show that a simple BB84 protocol
indeed distribute a binary sequence between Alice and Bob that looks almost
random for Eve with a probability exponentially close to 1.Comment: typos correcte
Fair and optimistic quantum contract signing
We present a fair and optimistic quantum contract signing protocol between
two clients that requires no communication with the third trusted party during
the exchange phase. We discuss its fairness and show that it is possible to
design such a protocol for which the probability of a dishonest client to cheat
becomes negligible, and scales as N^{-1/2}, where N is the number of messages
exchanged between the clients. Our protocol is not based on the exchange of
signed messages: its fairness is based on the laws of quantum mechanics. Thus,
it is abuse-free, and the clients do not have to generate new keys for each
message during the Exchange phase. We discuss a real-life scenario when the
measurement errors and qubit state corruption due to noisy channels occur and
argue that for real, good enough measurement apparatus and transmission
channels, our protocol would still be fair. Our protocol could be implemented
by today's technology, as it requires in essence the same type of apparatus as
the one needed for BB84 cryptographic protocol. Finally, we briefly discuss two
alternative versions of the protocol, one that uses only two states (based on
B92 protocol) and the other that uses entangled pairs, and show that it is
possible to generalize our protocol to an arbitrary number of clients.Comment: 11 pages, 2 figure
General theory for decoy-state quantum key distribution with arbitrary number of intensities
We develop a general theory for quantum key distribution (QKD) in both the
forward error correction and the reverse error correction cases when the QKD
system is equipped with phase-randomized coherent light with arbitrary number
of decoy intensities. For this purpose, generalizing Wang's expansion, we
derive a convex expansion of the phase-randomized coherent state. We also
numerically check that the asymptotic key generation rates are almost saturated
when the number of decoy intensities is three.Comment: This manuscript has been revised extensivel
Key distillation from quantum channels using two-way communication protocols
We provide a general formalism to characterize the cryptographic properties
of quantum channels in the realistic scenario where the two honest parties
employ prepare and measure protocols and the known two-way communication
reconciliation techniques. We obtain a necessary and sufficient condition to
distill a secret key using this type of schemes for Pauli qubit channels and
generalized Pauli channels in higher dimension. Our results can be applied to
standard protocols such as BB84 or six-state, giving a critical error rate of
20% and 27.6%, respectively. We explore several possibilities to enlarge these
bounds, without any improvement. These results suggest that there may exist
weakly entangling channels useless for key distribution using prepare and
measure schemes.Comment: 21 page
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