408 research outputs found
Spectra for the product of Gaussian noises
Products of Gaussian noises often emerge as the result of non-linear
detection techniques or as a parasitic effect, and their proper handling is
important in many practical applications, including in fluctuation-enhanced
sensing, indoor air or environmental quality monitoring, etc. We use Rice's
random phase oscillator formalism to calculate the power density spectra
variance for the product of two Gaussian band-limited white noises with
zero-mean and the same bandwidth W. The ensuing noise spectrum is found to
decrease linearly from zero frequency to 2W, and it is zero for frequencies
greater than 2W. Analogous calculations performed for the square of a single
Gaussian noise confirm earlier results. The spectrum at non-zero frequencies,
and the variance of the square of a noise, is amplified by a factor two as a
consequence of correlation effects between frequency products. Our analytic
results is corroborated by computer simulations.Comment: submitted for publicatio
Critical analysis of the Bennett-Riedel attack on secure cryptographic key distributions via the Kirchhoff-law-Johnson-noise scheme
Recently, Bennett and Riedel (BR) (http://arxiv.org/abs/1303.7435v1) argued that thermodynamics is not essential in the Kirchhoff-law–Johnson-noise (KLJN) classical physical cryptographic exchange method in an effort to disprove the security of the KLJN scheme. They attempted to demonstrate this by introducing a dissipation-free deterministic key exchange method with two batteries and two switches. In the present paper, we first show that BR's scheme is unphysical and that some elements of its assumptions violate basic protocols of secure communication. All our analyses are based on a technically unlimited Eve with infinitely accurate and fast measurements limited only by the laws of physics and statistics. For non-ideal situations and at active (invasive) attacks, the uncertainly principle between measurement duration and statistical errors makes it impossible for Eve to extract the key regardless of the accuracy or speed of her measurements. To show that thermodynamics and noise are essential for the security, we crack the BR system with 100% success via passive attacks, in ten different ways, and demonstrate that the same cracking methods do not function for the KLJN scheme that employs Johnson noise to provide security underpinned by the Second Law of Thermodynamics. We also present a critical analysis of some other claims by BR; for example, we prove that their equations for describing zero security do not apply to the KLJN scheme. Finally we give mathematical security proofs for each BR-attack against the KLJN scheme and conclude that the information theoretic (unconditional) security of the KLJN method has not been successfully challenged.Laszlo B. Kish, Derek Abbott, Claes G. Granqvis
Information theoretic security by the laws of classical physics
It has been shown recently that the use of two pairs of resistors with
enhanced Johnson-noise and a Kirchhoff-loop-i.e., a Kirchhoff-Law-Johnson-Noise
(KLJN) protocol-for secure key distribution leads to information theoretic
security levels superior to those of a quantum key distribution, including a
natural immunity against a man-in-the-middle attack. This issue is becoming
particularly timely because of the recent full cracks of practical quantum
communicators, as shown in numerous peer-reviewed publications. This
presentation first briefly surveys the KLJN system and then discusses related,
essential questions such as: what are perfect and imperfect security
characteristics of key distribution, and how can these two types of securities
be unconditional (or information theoretical)? Finally the presentation
contains a live demonstration.Comment: Featured in MIT Technology Review
http://www.technologyreview.com/view/428202/quantum-cryptography-outperformed-by-classical/
; Plenary talk at the 5th IEEE Workshop on Soft Computing Applications,
August 22-24, 2012, (SOFA 2012). Typos correcte
Fluctuation-enhanced gas sensing
AbstractThe sensitivity of gas sensors was earlier measured by classical method-comparison the resistance of sensors in gas media and air. Here we reported results of the study of low-frequency noise characteristics of sensors. We compare data for different Figaro TGS sensors as well as our sol-gel H2 tin dioxide and porous silicon sensors. The study was performed in dry air and in a mix of dry air with carbon monoxide, hydrogen and alcohol of different concentrations. Higher sensitivity of spectral dependence of noise (SDN) to gas concentration in comparison with classical method of the measurements of gas sensing by a change in the Ohmic resistance part of current-voltage characteristics of samples allows using such SND powerful method for determination of gas concentration in the air or environment
Non-linear microwave impedance of short and long Josephson Junctions
The non-linear dependence on applied field () or current () of the microwave (ac) impedance of both
short and long Josephson junctions is calculated under a variety of excitation
conditions. The dependence on the junction width is studied, for both field
symmetric (current anti-symmetric) and field anti-symmetric (current symmetric)
excitation configurations.The resistance shows step-like features every time a
fluxon (soliton) enters the junction, with a corresponding phase slip seen in
the reactance. For finite widths the interference of fluxons leads to some
interesting effects which are described. Many of these calculated results are
observed in microwave impedance measurements on intrinsic and fabricated
Josephson junctions in the high temperature superconductors, and new effects
are suggested. When a field () or current () is applied,
interesting phase locking effects are observed in the ac impedance
. In particular an almost periodic dependence on the dc bias is
seen similar to that observed in microwave experiments at very low dc field
bias. These results are generic to all systems with a potential
in the overdamped limit and subjected to an ac drive.Comment: 7 pages, 11 figure
Effect of Alkali Metal Atom Doping on the CuInSe2-Based Solar Cell Absorber
The efficiency of Cu(In,Ga)Se_2 (CIGS)-based solar cells can bemarkedly improved by controlled introduction of alkali metal (AM) atomsusing post-deposition treatment (PDT) after CIGS growth. Previous studieshave indicated that AM atoms may act as impurities or agglomerate intosecondary phases. To enable further progress, understanding of atomic levelprocesses responsible for these improvements is required. To this end, we haveinvestigated theoretically the effects of the AM elements Li, Na, K, Rb, and Cson the properties of the parent material CuInSe_2 . First, the effects of the AMimpurities in CuInSe_2 have been investigated in terms of formation energies,charge transition levels, and migration energy barriers. We found that AM atoms preferentially substitute for Cu atoms at theneutral charge state. Under In-poor conditions, AM atoms at the In site also show low formation energies and are acceptors. Themigration energy barriers show that the interstitial diffusion mechanism may be relevant only for Li, Na, and K, whereas all theAM atoms can diffuse with the help of Cu vacancies. The competition between these two mechanisms strongly depends on theconcentration of Cu vacancies. We also discuss how AM atoms can contribute to increasing Cu-depleted regions. Second, AMatoms can form secondary phases with Se and In atoms. We suggest a mechanism for the secondary phase formation followingthe PDT process. On the basis of the calculated reaction enthalpies and migration considerations, we find that mixed phases aremore likely in the case of LiInSe_2 and NaInSe_2 , whereas formation of secondary phases is expected for KInSe_2 , RbInSe_2 , andCsInSe_2 . We discuss our findings in the light of experimental results obtained for AM treatments. The secondary phases havelarge energy band gaps and improve the morphology of the buffer surface by enabling a favorable band alignment, which canimprove the electrical properties of the device. Moreover, they can also passivate the surface by forming a diffusion barrier.Overall, our work points to different roles played by the light and heavy AM atoms and suggests that both types may be neededto maximize their benefits on the solar cell performance.Peer reviewe
Search for Two-Neutrino Double Electron Capture of Xe with XENON100
Two-neutrino double electron capture is a rare nuclear decay where two
electrons are simultaneously captured from the atomic shell. For Xe
this process has not yet been observed and its detection would provide a new
reference for nuclear matrix element calculations. We have conducted a search
for two-neutrino double electron capture from the K-shell of Xe using
7636 kgd of data from the XENON100 dark matter detector. Using a
Bayesian analysis we observed no significant excess above background, leading
to a lower 90 % credibility limit on the half-life
yr. We also evaluated the sensitivity of the XENON1T experiment, which is
currently being commissioned, and find a sensitivity of
yr after an exposure of 2 tyr.Comment: 6 pages, 4 figure
The Large Enriched Germanium Experiment for Neutrinoless Double Beta Decay (LEGEND)
The observation of neutrinoless double-beta decay (0)
would show that lepton number is violated, reveal that neutrinos are Majorana
particles, and provide information on neutrino mass. A discovery-capable
experiment covering the inverted ordering region, with effective Majorana
neutrino masses of 15 - 50 meV, will require a tonne-scale experiment with
excellent energy resolution and extremely low backgrounds, at the level of
0.1 count /(FWHMtyr) in the region of the signal. The
current generation Ge experiments GERDA and the MAJORANA DEMONSTRATOR
utilizing high purity Germanium detectors with an intrinsic energy resolution
of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in
the 0 signal region of all 0
experiments. Building on this success, the LEGEND collaboration has been formed
to pursue a tonne-scale Ge experiment. The collaboration aims to develop
a phased 0 experimental program with discovery potential
at a half-life approaching or at years, using existing resources as
appropriate to expedite physics results.Comment: Proceedings of the MEDEX'17 meeting (Prague, May 29 - June 2, 2017
Removing krypton from xenon by cryogenic distillation to the ppq level
The XENON1T experiment aims for the direct detection of dark matter in a
cryostat filled with 3.3 tons of liquid xenon. In order to achieve the desired
sensitivity, the background induced by radioactive decays inside the detector
has to be sufficiently low. One major contributor is the -emitter
Kr which is an intrinsic contamination of the xenon. For the XENON1T
experiment a concentration of natural krypton in xenon Kr/Xe < 200
ppq (parts per quadrillion, 1 ppq = 10 mol/mol) is required. In this
work, the design of a novel cryogenic distillation column using the common
McCabe-Thiele approach is described. The system demonstrated a krypton
reduction factor of 6.410 with thermodynamic stability at process
speeds above 3 kg/h. The resulting concentration of Kr/Xe < 26 ppq
is the lowest ever achieved, almost one order of magnitude below the
requirements for XENON1T and even sufficient for future dark matter experiments
using liquid xenon, such as XENONnT and DARWIN
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