4,436 research outputs found
How Much Does Money Matter in a Direct Democracy?
The fine-structure splitting of quantum confined InxGa1-x Nexcitons is investigated using polarization-sensitive photoluminescence spectroscopy. The majority of the studied emission lines exhibits mutually orthogonal fine-structure components split by 100-340 mu eV, as measured from the cleaved edge of the sample. The exciton and the biexciton reveal identical magnitudes but reversed sign of the energy splitting.Original Publication:Supaluck Amloy, Y T Chen, K F Karlsson, K H Chen, H C Hsu, C L Hsiao, L C Chen and Per-Olof Holtz, Polarization-resolved fine-structure splitting of zero-dimensional InxGa1-xN excitons, 2011, PHYSICAL REVIEW B, (83), 20, 201307.http://dx.doi.org/10.1103/PhysRevB.83.201307Copyright: American Physical Societyhttp://www.aps.org
Polymers grafted to porous membranes
We study a single flexible chain molecule grafted to a membrane which has
pores of size slightly larger than the monomer size. On both sides of the
membrane there is the same solvent. When this solvent is good, i.e. when the
polymer is described by a self avoiding walk, it can fairly easily penetrate
the membrane, so that the average number of membrane crossings tends, for chain
length , to a positive constant. The average numbers of monomers on
either side of the membrane diverges in this limit, although their ratio
becomes infinite. For a poor solvent, in contrast, the entire polymer is
located, for large , on one side of the membrane. For good and for theta
solvents (ideal polymers) we find scaling laws, whose exponents can in the
latter case be easily understood from the behaviour of random walks.Comment: 4 pages, 6 figure
Charmful Three-body Baryonic B decays
We study the charmful three-body baryonic B decays with or
in the final state. We explain the measured rates of , , and and
predict the branching fractions of , , , and to be of order ,
respectively. They are readily accessible to the factories.Comment: 21 pages, 5 figures, version to appear in PR
Stretched Polymers in a Poor Solvent
Stretched polymers with attractive interaction are studied in two and three
dimensions. They are described by biased self-avoiding random walks with
nearest neighbour attraction. The bias corresponds to opposite forces applied
to the first and last monomers. We show that both in and a phase
transition occurs as this force is increased beyond a critical value, where the
polymer changes from a collapsed globule to a stretched configuration. This
transition is second order in and first order in . For we
predict the transition point quantitatively from properties of the unstretched
polymer. This is not possible in , but even there we can estimate the
transition point precisely, and we can study the scaling at temperatures
slightly below the collapse temperature of the unstretched polymer. We find
very large finite size corrections which would make very difficult the estimate
of the transition point from straightforward simulations.Comment: 10 pages, 16 figure
Quantum-Logic Gate between Two Optical Photons with an Average Efficiency above 40%
Optical qubits uniquely combine information transfer in optical fibers with a
good processing capability and are therefore attractive tools for quantum
technologies. A large challenge, however, is to overcome the low efficiency of
two-qubit logic gates. The experimentally achieved efficiency in an optical
controlled NOT (CNOT) gate reached approximately 11% in 2003 and has seen no
increase since. Here we report on a new platform that was designed to surpass
this long-standing record. The new scheme avoids inherently probabilistic
protocols and, instead, combines aspects of two established quantum nonlinear
systems: atom-cavity systems and Rydberg electromagnetically induced
transparency. We demonstrate a CNOT gate between two optical photons with an
average efficiency of 41.7(5)% at a postselected process fidelity of 81(2)%.
Moreover, we extend the scheme to a CNOT gate with multiple target qubits and
produce entangled states of presently up to five photons. All these
achievements are promising and have the potential to advance optical quantum
information processing in which almost all advanced protocols would profit from
high-efficiency logic gates.Comment: In this revision, we extend the discussion of the efficiency in Sec.
IV.C and we add models in appendices B, E, and L-
Experimental Studies of Low-field Landau Quantization in Two-dimensional Electron Systems in GaAs/AlGaAs Heterostructures
By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional
electron systems, we study the low-field Landau quantization when the thermal
damping is reduced with decreasing the temperature. Magneto-oscillations
following Shubnikov-de Haas (SdH) formula are observed even when their
amplitudes are so large that the deviation to such a formula is expected. Our
experimental results show the importance of the positive magneto-resistance to
the extension of SdH formula under the damping induced by the disorder.Comment: 9 pages, 3 figure
The key parameters controlling the photodesorption yield in interstellar CO ice analogs: Influence of ice deposition temperature and thickness
The overabundance of gas molecules in the coldest regions of space point to a
non-thermal desorption process. Laboratory simulations show an efficient
desorption of CO ice exposed to ultraviolet radiation, known as
photodesorption, which decreases for increasing ice deposition temperature.
However, the understanding of this abnormal phenomenon has remained elusive. In
this work we show the same phenomenon, and in particular, a dramatic drop in
the photodesorption yield is observed when the deposition temperature is 19 K
and higher. Also the minimum ice thickness that accounts for a constant
photodesorption yield of CO ice is deposition temperature dependent, an
observation reported here for the first time. We propose that the key
parameters that dominate the absorbed photon energy transfer in CO ice, and
contribute to the measured photodesorption yields are the energy transfer
length, single ice layer contributed desorption yield, and relative effective
surface area. This set of parameters should be incorporated in astrophysical
models that simulate photodesorption of the top CO-rich ice layer on icy dust
populations with the size distribution which is ice thickness related.Comment: 8 pages, 4 figure
Asymptotic Stability of the Relativistic Boltzmann Equation for the Soft Potentials
In this paper it is shown that unique solutions to the relativistic Boltzmann
equation exist for all time and decay with any polynomial rate towards their
steady state relativistic Maxwellian provided that the initial data starts out
sufficiently close in . If the initial data are continuous then
so is the corresponding solution. We work in the case of a spatially periodic
box. Conditions on the collision kernel are generic in the sense of
(Dudy{\'n}ski and Ekiel-Je{\.z}ewska, Comm. Math. Phys., 1988); this resolves
the open question of global existence for the soft potentials.Comment: 64 page
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