6,996 research outputs found
Multimode theory of measurement-induced non-Gaussian operation on wideband squeezed light
We present a multimode theory of non-Gaussian operation induced by an
imperfect on/off-type photon detector on a splitted beam from a wideband
squeezed light. The events are defined for finite time duration in the time
domain. The non-Gaussian output state is measured by the homodyne detector with
finite bandwidh . Under this time- and band-limitation to the quantm states,
we develop a formalism to evaluate the frequency mode matching between the
on/off trigger channel and the conditional signal beam in the homodyne channel.
Our formalism is applied to the CW and pulsed schemes. We explicitly calculate
the Wigner function of the conditional non-Gaussian output state in a realistic
situation. Good mode matching is achieved for BT\alt1, where the discreteness
of modes becomes prominant, and only a few modes become dominant both in the
on/off and the homodyne channels. If the trigger beam is projected nearly onto
the single photon state in the most dominant mode in this regime, the most
striking non-classical effect will be observed in the homodyne statistics. The
increase of and the dark counts degrades the non-classical effect.Comment: 20 pages, 14 figures, submitted to Phys. Rev.
Pulsars: Gigantic Nuclei
What is the real nature of pulsars? This is essentially a question of the
fundamental strong interaction between quarks at low-energy scale and hence of
the non-perturbative quantum chromo-dynamics, the solution of which would
certainly be meaningful for us to understand one of the seven millennium prize
problems (i.e., "Yang-Mills Theory") named by the Clay Mathematical Institute.
After a historical note, it is argued here that a pulsar is very similar to an
extremely big nucleus, but is a little bit different from the {\em gigantic
nucleus} speculated 80 years ago by L. Landau. The paper demonstrates the
similarity between pulsars and gigantic nuclei from both points of view: the
different manifestations of compact stars and the general behavior of the
strong interaction.Comment: 8 pages, 1 figures; Comments welcome
Equilibrium magnetization in the vicinity of the first order phase transition in the mixed state of high-Tc superconductors
We present the results of a scaling analysis of isothermal magnetization M(H)
curves measured in the mixed state of high-Tc superconductors in the vicinity
of the established first order phase transition. The most surprising result of
our analysis is that the difference between the magnetization above and below
the transition may have either sign, depending on the particular chosen sample.
We argue that this observation, based on M(H) data available in the literature,
is inconsistent with the interpretation that the well known first order phase
transition in the mixed state of high-Tc superconductors always represents the
melting transition in the vortex system.Comment: 4 pages, 5 figure
Analytical solutions of the Schr\"{o}dinger equation with the Woods-Saxon potential for arbitrary state
In this work, the analytical solution of the radial Schr\"{o}dinger equation
for the Woods-Saxon potential is presented. In our calculations, we have
applied the Nikiforov-Uvarov method by using the Pekeris approximation to the
centrifugal potential for arbitrary states. The bound state energy
eigenvalues and corresponding eigenfunctions are obtained for various values of
and quantum numbers.Comment: 14 page
Activation barrier scaling and crossover for noise-induced switching in a micromechanical parametric oscillator
We explore fluctuation-induced switching in a parametrically-driven
micromechanical torsional oscillator. The oscillator possesses one, two or
three stable attractors depending on the modulation frequency. Noise induces
transitions between the coexisting attractors. Near the bifurcation points, the
activation barriers are found to have a power law dependence on frequency
detuning with critical exponents that are in agreement with predicted universal
scaling relationships. At large detuning, we observe a crossover to a different
power law dependence with an exponent that is device specific.Comment: 5 pages, 5 figure
Electron-electron scattering effect on spin relaxation in multi-valley nanostructures
We develop a theory of effects of electron-electron collisions on the
Dyakonov-Perel' spin relaxation in multi-valley quantum wells. It is shown that
the electron-electron scattering rate which governs the spin relaxation is
different from that in a single-valley system. The theory is applied to Si/SiGe
(001)-grown quantum wells where two valleys are simultaneously populated by
free carriers. The dependences of the spin relaxation rate on temperature,
electron concentration and valley-orbit splitting are calculated and discussed.
We demonstrate that in a wide range of temperatures the electron-electron
collisions can govern spin relaxation in high-quality Si/SiGe quantum wells.Comment: 6 pages, 4 figures, EPL style, revised versio
Universality in adsorbate ordering on nanotube surfaces
Numerically efficient transfer matrix technique for studying statistics of
coherent adsorbates on small nanotubes has been developed. In the framework of
a realistic microscopic model fitted to the data of ab initio calculations
taken from literature sources, the ordering of potassium adsorbate on (6,0)
single-walled carbon nanotube has been studied. Special attention has been
payed to the phase transition-like abrupt changes seen in the adsorption
isotherms at low temperature. It has been found that the behavior during the
transitions conforms with the universality hypothesis of the theory of critical
phenomena and is qualitatively the same as in the one dimensional Ising model.
Quantitatively the critical behavior can be fully described by two parameters.
Their qualitative connection with the properties of interphase boundaries is
suggested but further research is needed to develop a quantitative theory.Comment: 11 pages, 6 figures; some typos correcte
Critical currents, flux-creep activation energy and potential barriers for the vortex motion from the flux creep experiments
We present an experimental study of thermally activated flux creep in a
superconducting ring-shaped epitaxial YBCO film as well as a new way of
analyzing the experimental data. The measurements were made in a wide range of
temperatures between 10 and 83 K. The upper temperature limit was dictated by
our experimental technique and at low temperatures we were limited by a
crossover to quantum tunneling of vortices. It is shown that the experimental
data can very well be described by assuming a simple thermally activated
hopping of vortices or vortex bundles over potential barriers, whereby the
hopping flux objects remain the same for all currents and temperatures. The new
procedure of data analysis also allows to establish the current and temperature
dependencies of the flux-creep activation energy U, as well as the temperature
dependence of the critical current Ic, from the flux-creep rates measured at
different temperatures. The variation of the activation energy with current,
U(I/Ic), is then used to reconstruct the profile of the potential barriers in
real space.Comment: 12 pages, 13 Postscript figures, Submitted to Physical Review
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