14,957 research outputs found
Thermally induced 0-pi phase transition in Josephson junctions through a ferromagnetic oxide film
We investigate the Josephson transport through a ferromagnetic oxide film,
e.g., LaBaCuO, theoretically. Using the recursive Green's function
technique, we found the formation of a pi-junction in such systems. Moreover
the 0-pi phase transition is induced by increasing the temperature. Such
ferromagnetic-oxide based Josephson junctions may become an element in the
architecture of future quantum computers.Comment: 4 pages, 3 figure
Atomic scale 0-pi transition in a high-Tc superconductor/ferromagnetic-insulator/high-T superconductor Josephson junction
We study the Josephson transport in a high-Tc
superconductor/ferromagnetic-insulator(FI)/high-Tc superconductor numerically.
We found the formation of a pi-junction in such systems. More remarkably the
ground state of such junction alternates between 0- and pi-states when
thickness of FI is increasing by a single atomic layer. We propose an
experimental setup for observing the atomic-scale 0-pi transition. Such
FI-based pi-junctions can be used to implement highly-coherent quantum bits.Comment: 4 pages, 3 figure
Critical Temperature T_c versus Charging Energy E_c in MgB2 and C60/CHBr3
The boride compounds MB_x related to the magnesium-boron stacking layered
material MgB2 are discussed in terms of the B-B layers in the borides analogous
to the Cu-O ones in the cuprates. We propose a possibility of superconducting
materials which exhibit higher critical temperature T_c than 39 K of MgB2. We
point out a role of interstitial ionic atoms M (e.g., Mg in MgB2) as
capacitors, which reduce the condensation-energy loss due to the charging
energy E_c between the B-B layers. In the viewpoint of the present model, the
recently discovered 117-Kelvin superconductor C60/CHBr3 is also discussed in
terms of the intercalation molecules CHBr3 as possible capacitors among the
superconducting grains of C60 molecules.Comment: 9 pages, 1 fugure included; prepared for Proceedings of the symposium
ISS2001, Kobe, Sep. 200
Effect of d-f hybridization on the Josephson current through Eu-chalcogenides
A superconducting ring with a pi junction made from
superconductor/ferromagnetic-metal/superconductor (S-FM-S) exhibits a
spontaneous current without an external magnetic field in the ground state.
Such pi ring provides so-called quiet qubit that can be efficiently decoupled
from the fluctuation of the external field. However, the usage of the FM gives
rise to strong Ohmic dissipation. Therefore, the realization of pi junctions
without FM is expected for qubit applications. We theoretically consider the
possibility of the pi coupling for S/Eu-chalcogenides/S junctions based on the
d-f Hamiltonian. By use of the Green's function method we found that pi
junction can be formed in the case of the finite d-f hybridization between the
conduction d and the localized f electrons.Comment: 4 pages, 4 figure
New method for precise determination of top quark mass at LHC
A new method to measure the mass of the top quark at the LHC is presented.
This method uses lepton energy distribution and ideally does not depend on the
velocity distribution of the top quark. We perform a simulation analysis of the
top quark mass reconstruction using this method at the leading order, taking
account of experimental circumstances. We estimate the sensitivity of the mass
determination. The results show that this method is viable in realistic
experimental conditions and has a possibility to achieve a good accuracy in
determining a theoretically well-defined top quark mass by including
higher-order corrections.Comment: 5 pages, 5 figures, Proceedings of the 37th International Conference
on High Energy Physics (ICHEP 2014
Statistical methods for estimating tephra source and dispersal : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Statistics at Massey University, Palmerston North, New Zealand
Tephra refers to any pyroclastic fragments ejected from a volcanic vent and its dispersal
is one of the major hazards with explosive eruptions. The attenuation of tephra fall
thickness is most commonly estimated after contouring field measurements into smooth
isopachs. I explicitly describe the variability in thickness by using a semiempirical
tephra attenuation relation as a link function. This opens the way to fitting models
to actual tephra observations through maximum likelihood estimation (MLE). The
method is illustrated using data published from the 1973 Heimaey eruption in Iceland.
Complex eruptions commonly produce several phases of tephra fall from multiple vents.
When attempting to precisely reconstruct past eruptions from the geological record
alone, separate phases are often indistinguishable. Augmented by a mixture framework,
the MLE attenuation model was able to identify the sources and directions of tephra
deposition for the 1977 Ukinrek Maars eruption in Alaska, US, from only the tephra
thickness data. It was then applied to the unobserved 1256 AD Al-Madinah eruption
in Saudi Arabia.
The estimation of the spatio-temporal hazard from a monogenetic volcanic field is criti-
cally dependent on a reconstruction of past events. The Auckland Volcanic Field (AVF)
has produced about 50 volcanoes in the last 250,000 years. Although inconsistent, age
data for many of these volcanoes exist from various dating methods with various re-
liabilities. The age order of some pairs is also known due to the overlaying of lavas
(stratigraphy). A discussion is provided on how informative priors are obtained via ex-
pert elicitation, on both the individual volcano ages, and the reliabilities of the dating
methods. A possible Bayesian model for reconciling the available inconsistent volcano
age data to estimate the true eruption ages is also discussed.
To improve these eruption age estimates, some of the volcanoes can be correlated with
the better dated tephra layers recovered from five maars in the field. The likelihood of
any combination of volcano and tephra, incorporating the spatial variability based on
the attenuation model and temporal components, is evaluated and is maximised numer-
ically using linear programming. This statistical matching provides an improvement in
the volcano age-order model and age estimates of the volcanoes in the AVF
Quantum Information Processing and Entanglement in Solid State Devices
Control over electron-spin states, such as coherent manipulation, filtering
and measurement promises access to new technologies in conventional as well as
in quantum computation and quantum communication. In this paper, we review
recent theoretical proposal of using electron spins in quantum confined
structures as qubits. We also present a theoretical proposal for testing Bell's
inequality in nano-electronics devices. We show that the entanglement of two
electron spins can be detected in the spin filter effect in the nanostructure
semiconductor / ferromagnetic semiconductor / semiconductor junction. In
particular, we show how to test Bell's inequality via the measurement of the
current-current correlation function in this setup.Comment: 7 pages, 5 figure
- âŠ