85 research outputs found
Adsorption and desorption of deuterium on partially oxidized Si(100) surfaces
Adsorption and desorption of deuterium are studied on the partially oxidized Si(100) surfaces. The partial oxygen coverage causes a decrease in the initial adsorption probability of D atoms. The observed D2 temperature-programmed-desorption (TPD) spectra comprise of multiple components depending on the oxygen coverage (θO). For θO=0.1ML the D2 TPD spectrum is deconvoluted into four components, each of which has a peak in the temperature region higher than the D2 TPD peaking at 780 K on the oxygen free surface. The highest TPD component with a peak around 1040 K is attributed to D adatoms on Si dimers backbonded by an oxygen atom. The other components are attributed to D adatoms on the nearest or second nearest sites of the O-backbonded Si dimers. D adatoms on the partially oxidized Si surfaces are abstracted by gaseous H atoms along two different abstraction pathways: one is the pathway along direct abstraction (ABS) to form HD molecules and the other is the pathway along indirect abstraction via collision-induced-desorption (CID) of D adatoms to form D2 molecules. The ABS pathway is less seriously affected by oxygen adatoms. On the other hand, the CID pathway receives a strong influence of oxygen adatoms since the range of surface temperature effective for CID is found to considerably shift to higher surface temperatures with increasing θO. Gradual substitution of D adatoms with H atoms during H exposure results in HD desorption along the CID pathway in addition to the ABS one. By employing a modulated beam technique the CID-related HD desorption is directly distinguished from the ABS-related one
Instantons, Monopoles and the Flux Quantization in the Faddeev-Niemi Decomposition
We study how instantons arise in the low energy effective theory of the SU(2)
Yang-Mills theory in the context of the non-linear sigma model recently propose
by Faddeev and Niemi. We find a simple relation between the instanton number
and the charge m of the monopole that appears in the effective theory. It
is given by , where is the quantized flux
associated with a U(1) gauge field passing through the loop formed by the
singularity of the monopole.Comment: Tex, 12 pages, 3 figures (eps), references adde
Abelian Decomposition of Sp(2N) Yang-Mills Theory
In the previous paper, we generalized the method of Abelian decomposition to
the case of SO(N) Yang-Mills theory. This method that was proposed by Faddeev
and Niemi introduces a set of variables for describing the infrared limit of a
Yang-Mills theory. Here, we extend the decomposition method further to the
general case of four-dimensional Sp(2N) Yang-Mills theory. We find that the
Sp(2N) connection decomposes according to irreducible representations of SO(N).Comment: latex, 8 page
Concise and Tight Security Analysis of the Bennett-Brassard 1984 Protocol with Finite Key Lengths
We present a tight security analysis of the Bennett-Brassard 1984 protocol
taking into account the finite size effect of key distillation, and achieving
unconditional security. We begin by presenting a concise analysis utilizing the
normal approximation of the hypergeometric function. Then next we show that a
similarly tight bound can also be obtained by a rigorous argument without
relying on any approximation. In particular, for the convenience of
experimentalists who wish to evaluate the security of their QKD systems, we
also give explicit procedures of our key distillation, and also show how to
calculate the secret key rate and the security parameter from a given set of
experimental parameters. Besides the exact values of key rates and security
parameters, we also present how to obtain their rough estimates using the
normal approximation.Comment: 40 pages, 4 figures, revised arguments on security, and detailed
explanaions on how to use theoretical result
Decomposition of meron configuration of SU(2) gauge field
For the meron configuration of the SU(2) gauge field in the four dimensional
Minkowskii spacetime, the decomposition into an isovector field \bn,
isoscalar fields and , and a U(1) gauge field is
attained by solving the consistency condition for \bn. The resulting \bn
turns out to possess two singular points, behave like a monopole-antimonopole
pair and reduce to the conventional hedgehog in a special case. The
field also possesses singular points, while and are regular
everywhere.Comment: 18 pages, 5 figures, Sec.4 rewritten. 5 refs. adde
Magnetic monopoles vs. Hopf defects in the Laplacian (Abelian) gauge
We investigate the Laplacian Abelian gauge on the sphere S^4 in the
background of a single `t Hooft instanton. To this end we solve the eigenvalue
problem of the covariant Laplace operator in the adjoint representation. The
ground state wave function serves as an auxiliary Higgs field. We find that the
ground state is always degenerate and has nodes. Upon diagonalisation, these
zeros induce toplogical defects in the gauge potentials. The nature of the
defects crucially depends on the order of the zeros. For first-order zeros one
obtains magnetic monopoles. The generic defects, however, arise from zeros of
second order and are pointlike. Their topological invariant is the Hopf index
S^3 -> S^2. These findings are corroborated by an analysis of the Laplacian
gauge in the fundamental representation where similar defects occur. Possible
implications for the confinement scenario are discussed.Comment: 18 pages, 3 figure
Flipping quantum coins
Coin flipping is a cryptographic primitive in which two distrustful parties
wish to generate a random bit in order to choose between two alternatives. This
task is impossible to realize when it relies solely on the asynchronous
exchange of classical bits: one dishonest player has complete control over the
final outcome. It is only when coin flipping is supplemented with quantum
communication that this problem can be alleviated, although partial bias
remains. Unfortunately, practical systems are subject to loss of quantum data,
which restores complete or nearly complete bias in previous protocols. We
report herein on the first implementation of a quantum coin-flipping protocol
that is impervious to loss. Moreover, in the presence of unavoidable
experimental noise, we propose to use this protocol sequentially to implement
many coin flips, which guarantees that a cheater unwillingly reveals
asymptotically, through an increased error rate, how many outcomes have been
fixed. Hence, we demonstrate for the first time the possibility of flipping
coins in a realistic setting. Flipping quantum coins thereby joins quantum key
distribution as one of the few currently practical applications of quantum
communication. We anticipate our findings to be useful for various
cryptographic protocols and other applications, such as an online casino, in
which a possibly unlimited number of coin flips has to be performed and where
each player is free to decide at any time whether to continue playing or not.Comment: 17 pages, 3 figure
Instantons and Monopoles in General Abelian Gauges
A relation between the total instanton number and the quantum-numbers of
magnetic monopoles that arise in general Abelian gauges in SU(2) Yang-Mills
theory is established. The instanton number is expressed as the sum of the
`twists' of all monopoles, where the twist is related to a generalized Hopf
invariant. The origin of a stronger relation between instantons and monopoles
in the Polyakov gauge is discussed.Comment: 28 pages, 8 figures; comments added to put work into proper contex
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