268 research outputs found
A quantum key distribution protocol for rapid denial of service detection
We introduce a quantum key distribution protocol designed to expose fake
users that connect to Alice or Bob for the purpose of monopolising the link and
denying service. It inherently resists attempts to exhaust Alice and Bob's
initial shared secret, and is 100% efficient, regardless of the number of
qubits exchanged above the finite key limit. Additionally, secure key can be
generated from two-photon pulses, without having to make any extra
modifications. This is made possible by relaxing the security of BB84 to that
of the quantum-safe block cipher used for day-to-day encryption, meaning the
overall security remains unaffected for useful real-world cryptosystems such as
AES-GCM being keyed with quantum devices.Comment: 13 pages, 3 figures. v2: Shifted focus of paper towards DoS and added
protocol 4. v1: Accepted to QCrypt 201
Quantum entanglement distribution with 810 nm photons through telecom fibers
We demonstrate the distribution of polarization entangled photons of
wavelength 810 nm through standard telecom fibers. This technique allows
quantum communication protocols to be performed over established fiber
infrastructure, and makes use of the smaller and better performing setups
available around 800 nm, as compared to those which use telecom wavelengths
around 1550 nm. We examine the excitation and subsequent quenching of
higher-order spatial modes in telecom fibers up to 6 km in length, and perform
a distribution of high quality entanglement (visibility 95.6%). Finally, we
demonstrate quantum key distribution using entangled 810 nm photons over a 4.4
km long installed telecom fiber link.Comment: 5 pages, 5 figures, 1 tabl
Studying Free-Space Transmission Statistics and Improving Free-Space QKD in the Turbulent Atmosphere
The statistical fluctuations in free-space links in the turbulent atmosphere
are important for the distribution of quantum signals. To that end, we first
study statistics generated by the turbulent atmosphere in an entanglement based
free-space quantum key distribution (QKD) system. Using the insights gained
from this analysis, we study the effect of link fluctuations on the security
and key generation rate of decoy state QKD concluding that it has minimal
effect in the typical operating regimes. We then investigate the novel idea of
using these turbulent fluctuations to our advantage in QKD experiments. We
implement a signal-to-noise ratio filter (SNRF) in our QKD system which rejects
measurements during periods of low transmission efficiency, where the measured
quantum bit error rate (QBER) is temporarily elevated. Using this, we increase
the total secret key generated by the system from 78,009 bits to 97,678 bits,
representing an increase of 25.2% in the final secure key rate, generated from
the same raw signals. Lastly, we present simulations of a QKD exchange with an
orbiting LEO satellite and show that an SNRF will be extremely useful in such a
situation, allowing many more passes to extract a secret key than would
otherwise be possible.Comment: 9 pages, 6 figure
Inappropriate Implantable Cardioverter-Defibrillator Shocks Incidence, Predictors, and Impact on Mortality
ObjectivesThe purpose of this study was to assess the incidence, predictors, and outcome of inappropriate shocks in implantable cardioverter-defibrillator (ICD) patients.BackgroundDespite the benefits of ICD therapy, inappropriate defibrillator shocks continue to be a significant drawback. The prognostic importance of inappropriate shocks outside the setting of a clinical trial remains unclear.MethodsFrom 1996 to 2006, all recipients of defibrillator devices equipped with intracardiac electrogram storage were included in the current analysis and clinically assessed at implantation. During follow-up, the occurrence of inappropriate ICD shocks and all-cause mortality was noted.ResultsA total of 1,544 ICD patients (79% male, age 61 ± 13 years) were included in the analysis. During the follow-up period of 41 ± 18 months, 13% experienced ≥1 inappropriate shocks. The cumulative incidence steadily increased to 18% at 5-year follow-up. Independent predictors of the occurrence of inappropriate shocks included a history of atrial fibrillation (hazard ratio [HR]: 2.0, p < 0.01) and age younger than 70 years (HR: 1.8, p = 0.01). Experiencing a single inappropriate shock resulted in an increased risk of all-cause mortality (HR: 1.6, p = 0.01). Mortality risk increased with every subsequent shock, up to an HR of 3.7 after 5 inappropriate shocks.ConclusionsIn a large cohort of ICD patients, inappropriate shocks were common. The most important finding is the association between inappropriate shocks and mortality, independent of interim appropriate shocks
Prognostic Importance of Atrial Fibrillation in Implantable Cardioverter-Defibrillator Patients
ObjectivesThis study aimed to assess the prevalence of different types of atrial fibrillation (AF) and their prognostic importance in implantable cardioverter-defibrillator (ICD) patients.BackgroundThe prevalence of AF has taken epidemic proportions in the population with cardiovascular disease. The prognostic importance of different types of AF in ICD patients remains unclear.MethodsData on 913 consecutive patients (79% men, mean age 62 ± 13 years) receiving an ICD at the Leiden University Medical Center were prospectively collected. Among other characteristics, the existence and type of AF (paroxysmal, persistent, or permanent) were assessed at implantation. During follow-up, the occurrence of appropriate or inappropriate device therapy as well as mortality was noted.ResultsAt implantation, 73% of patients had no history of AF, 9% had a history of paroxysmal AF, 7% had a history of persistent AF, and 11% had permanent AF. During 833 ± 394 days of follow-up, 117 (13%) patients died, 228 (25%) patients experienced appropriate device discharge, and 139 (15%) patients received inappropriate shocks. Patients with permanent AF exhibited more than double the risk of mortality, ventricular arrhythmias triggering device discharge, and inappropriate device therapy. Patients with paroxysmal or persistent AF did not show a significant increased risk of mortality or appropriate device therapy but demonstrated almost 3 times the risk of inappropriate device therapy.ConclusionsIn the population currently receiving ICD treatment outside the setting of clinical trials, a large portion has either a history of AF or permanent AF. Both types of AF have prognostic implications for mortality and appropriate as well as inappropriate device discharge
Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility
The search for 4He-eta bound states was performed with the WASA-at-COSY
facility via the measurement of the excitation function for the dd->3He n pi0
and dd->3He p pi- processes. The beam momentum was varied continuously between
2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He
eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined
based on the dd->3He n reaction and quasi-free proton-proton scattering via
dd->pp n_spectator n_spectator reactions. The excitation functions determined
independently for the measured reactions do not reveal a structure which could
be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the
total cross sections for the bound state production and decay in
dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes
were determined taking into account the isospin relation between both the
channels considered. The results of the analysis depend on the assumptions of
the N* momentum distribution in the anticipated mesic-4He. Assuming as in the
previous works, that this is identical with the distribution of nucleons bound
with 20 MeV in 4He, we determined that (for the mesic bound state width in the
range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about
3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on
the recent theoretical findings of the N*(1535) momentum distribution in the
N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector
acceptance decreases and hence the corresponding upper limits are 5 nb and 10
nb for npi0 and ppi- channels respectively.Comment: This article will be submitted to JHE
Charge Symmetry Breaking in dd->4He{\pi}0 with WASA-at-COSY
Charge symmetry breaking (CSB) observables are a suitable experimental tool
to examine effects induced by quark masses on the nuclear level. Previous high
precision data from TRIUMF and IUCF are currently used to develop a consistent
description of CSB within the framework of chiral perturbation theory. In this
work the experimental studies on the reaction dd->4He{\pi}0 have been extended
towards higher excess energies in order to provide information on the
contribution of p-waves in the final state. For this, an exclusive measurement
has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY
facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +-
13(sys) +- 8(ext)) pb and first data on the differential cross section are
consistent with s-wave pion production.Comment: 14 pages, 5 figure
ABC Effect and Resonance Structure in the Double-Pionic Fusion to He
Exclusive and kinematically complete measurements of the double pionic fusion
to He have been performed in the energy region of the so-called ABC effect,
which denotes a pronounced low-mass enhancement in the -invariant mass
spectrum. The experiments were carried out with the WASA detector setup at
COSY. Similar to the observations in the basic reaction
and in the He reaction, the data reveal a correlation
between the ABC effect and a resonance-like energy dependence in the total
cross section. Differential cross sections are well described by the hypothesis
of resonance formation during the reaction process in addition to the
conventional -channel mechanism. The deduced resonance
width can be understood from collision broadening due to Fermi motion of the
nucleons in initial and final nuclei
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