共查询到20条相似文献,搜索用时 797 毫秒
1.
S.U. Addicks A. Beige M. Dakna G.C. Hegerfeldt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(3):393-404
Cooperative effects in the fluorescence of two dipole-interacting atoms, with macroscopic quantum jumps (light and dark periods),
are investigated. The transition rates between different intensity periods are calculated in closed form and are used to determine
the rates of double jumps between periods of double intensity and dark periods, the mean duration of the three intensity periods
and the mean rate of their occurrence. We predict, to our knowledge for the first time, cooperative effects for double jumps,
for atomic distances from one and to ten wave lengths of the strong transition. The double jump rate, as a function of the
atomic distance, can show oscillations of up to 30% at distances of about a wave length, and oscillations are still noticeable
at a distance of ten wave lengths. The cooperative effects of the quantities and their characteristic behavior turn out to
be strongly dependent on the laser detuning.
Received 19 March 2001 and Received in final form 13 June 2001 相似文献
2.
Z. Haba H. Kleinert 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(4):553-560
We set up a forward - backward path integral for a point particle in a bath of photons to derive a master equation for the
density matrix which describes electromagnetic dissipation and decoherence. We also derive the associated Langevin equation.
As an application, we recalculate the Wigner-Weisskopf formula for the natural line width of an atomic state at zero temperature
and find, in addition, the temperature broadening caused by the decoherence term. Our master equation also yields the correct
Lamb shift of atomic levels. The two equations may have applications to dilute interstellar gases or to few-particle systems
in cavities.
Received 29 November 2000 and Received in final form 11 February 2001 相似文献
3.
M. Kuperman D. Zanette 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):387-391
We analyze the phenomenon of stochastic resonance in an Ising-like system on a small-world network. The system, which is subject
to the combined action of noise and an external modulation, can be interpreted as a stylized model of opinion formation by
imitation under the effects of a “fashion wave”. Both the amplitude threshold for the detection of the external modulation
and the width of the stochastic-resonance peak show considerable variation as the randomness of the underlying small-world
network is changed.
Received 19 December 2001 相似文献
4.
N. Liu W. Gao J. Yin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):137-145
A new scheme to magnetically guide cold, neutral atoms using a V-shaped current-carrying conductor is proposed. The spatial
distributions of the magnetic fields, potentials and forces generated by the V-shaped current-carrying conductor are calculated,
and the relationship between the magnetic field and the parameters of the V-shaped current-carrying conductor are analyzed
in detail. Our study shows that the V-shaped current-carrying conductor proposed here can be used to guide cold atoms in the
weak-field-seeking state, and to construct various atom-optical elements, such as atomic funnel, atomic beam-splitter and
atom interferometer and so on, and even to realize a single-mode atomic waveguiding under certain conditions.
Received 17 November 2000 and Received in final form 26 May 2001 相似文献
5.
F. Levi A. Godone J. Vanier S. Micalizio G. Modugno 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):53-59
The paper is concerned with the line shapes of resonance phenomena observed in Coherent Population Trapping (CPT) applied
to alkali atoms in a cell containing a buffer gas. Significant asymmetries and departures from a Lorentzian shape have been
observed in connection with the measurement of dark lines and CPT maser emission profiles. Measurements are reported as a
function of the power and frequency tuning of the laser used to create the CPT phenomenon. The paper reports on different
experimental conditions and a comparison between theory and experiments is made for the cases of cesium and rubidium in a
buffer gas.
Received 3 March 2000 and Received in final form 10 April 2000 相似文献
6.
D.G. Angelakis P.L. Knight 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):247-250
We show how entangled atomic pairs can be prepared in order to test the Bell inequalities. The scheme is based on the interaction
of the atoms with a highly localized field mode within a photonic crystal. The potential of using optically separated transitions
and the stability of the entangled state to spontaneous emission could lead to the closure of the communication and the detection
loopholes appearing in experiments so far. The robustness of the scheme against detector inefficiencies, the spread in the
atomic velocities and the fact that the entangled pairs are not generated simultaneously is also studied.
Received 31 July 2001 and Received in final form 30 November 2001 相似文献
7.
G. Li S. Wu P. Zhou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):267-277
The dressed-state populations and the resonance fluorescence spectrum of a V-type three-level atom driven by a strong coherent
field and a weak stochastic one simultaneously are investigated. There can be significant population inversion due to the
effect of the stochastic field. The atomic resonance fluorescence spectrum can be controlled by adjusting the frequency difference
between the coherent field and the stochastic one and the coherent Rabi frequency. Peak suppression and line narrowing occur
under appropriate conditions.
Received 23 June 2000 and Received in final form 18 January 2001 相似文献
8.
Z. Ficek J. Seke A.V. Soldatov G. Adam N.N. Bogolubov Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):411-419
We investigate the absorption and dispersion properties of a two-level atom driven by a polychromatic field. The driving field
is composed of a strong resonant (carrier) frequency component and a large number of symmetrically detuned sideband fields
(modulators). A rapid increase in the absorption at the central frequency and the collapse of the response of the system from
multiple frequencies to a single frequency are predicted to occur when the Rabi frequency of the modulating fields is equal
to the Rabi frequency of the carrier field. These are manifestations of the undressing or a disentanglement of the atomic
and driving field states, that leads to a collapse of the atom to its ground state. Our calculation permits consideration
of the question of the undressing of the driven atom by a multiple-modulated field and the predicted spectra offer a method
of observing undressing. Moreover, we find that the absorption and dispersion spectra split into multiplets whose structures
depend on the Rabi frequency of the modulating fields. The spectral features can jump between different resonance frequencies
by changing the Rabi frequency of the modulating fields or their initial phases, which can have potential applications as
a quantum frequency filter.
Received 23 October 2001 and Received in final form 31 January 2002 相似文献
9.
Room temperature stable single-photon source 总被引:2,自引:0,他引:2
A. Beveratos S. Kühn R. Brouri T. Gacoin J.-P. Poizat P. Grangier 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(2):191-196
We report on the realization of a stable solid state room temperature source for single photons. It is based on the fluorescence
of a single nitrogen-vacancy (NV) color center in a diamond nanocrystal. Antibunching has been observed in the fluorescence
light under both continuous and pulsed excitation. Our source delivers 2×104 s-1 single-photon pulses at an excitation repetition rate of 10 MHz. The number of two-photon pulses is reduced by a factor of
five compared to strongly attenuated coherent sources.
Received 1st August 2001 and Received in final form 2 October 2001 相似文献
10.
Ellison CJ Kim SD Hall DB Torkelson JM 《The European physical journal. E, Soft matter》2002,8(2):155-166
Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine
the effects of decreasing film thickness on glass transition temperature, T
g, the relative strength of the glass transition, and the relative rate of physical aging below T
g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state
of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine)
(P2VP) differs from that in the rubbery state with a transition at T
g. Positive deviations from bulk T
g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T
g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence
intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength
of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful
information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when
used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of
physical aging in films as thin as 10 nm.
Received 21 August 2001 相似文献
11.
U. Kentsch T. Werner G. Zschornack F. Grossmann V.P. Ovsyannikov F. Ullmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):297-305
Irq+ ( 41≤q≤64) ions with open-shell configurations have been produced in the electron beam of the room-temperature Dresden Electron
Beam Ion Trap (Dresden EBIT) at electron excitation energies from 2 keV to 13 keV. X-ray emission from direct excitation processes
and radiative capture in krypton-like to aluminium-like iridium ions is measured with an energy dispersive Si(Li) detector.
The detected X-ray lines are analyzed and compared with results from multiconfigurational Dirac-Fock (MCDF) atomic structure
calculations. This allows to determine dominant produced ion charge states at different electron energies. The analysis shows
that at the realized working gas pressure of 5×10-9mbar for higher charged ions the maximum ion charge state is not preferently determined by the chosen electron beam energy
needed for ionization of certain atomic substates, but by the balance between ionization and charge state reducing processes
as charge exchange and radiative recombination. This behaviour is also discussed on the basis of model calculations for the
resulting ion charge state distribution.
Received 12 July 2001 and Received in final form 10 September 2001 相似文献
12.
M. Genovese C. Novero 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):109-113
We propose a quantum transmission based on bi-photons, which are doubly-entangled both in polarisation and phase. This scheme
finds a natural application in quantum cryptography, where we show that an eventual eavesdropper is bound to introduce a larger
error on the quantum communication than for a single entangled bi-photon communication, when he steels the same information.
Received 23 July 2001 / Received in final form 30 November 2001 Published online 24 September 2002 相似文献
13.
Column size effects of DER fluids 总被引:1,自引:0,他引:1
The static yield stress of dielectric electrorheological (DER) fluids of infinite column state and chain state are calculated
from the first principle method. The results indicate that the column surface contributions to ER effects is very small and
both states will give correct results to the real DER fluids.
Received 29 January 2001 and Received in final form 30 April 2001 相似文献
14.
15.
J. A. Pomarico D. I. Iriarte H. O. Di Rocco 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):65-72
In this paper we analyze the variations in line intensities ratios due to a non-equilibrium situation and to optical depth
effects. A four level model is proposed and the two particular situations for the possible transitions are considered. Electron
density and temperature as well as the source thickness are used as independent parameters to find out in which way and extent
they modify the ratios of levels populations compared with the ideal case of an equilibrium state and optically thin source.
Accordingly with the ion of interest, electron temperatures ranging from I/20 to I/7 eV (I being the ionization energy), whereas electron densities in the interval from 1014 to 1020 cm-3 will be considered. These ranges are of special interest for diverse applications such as LIBS and measurement of transition
probabilities. Some results are presented for real ions and a new expression for the escape factor is also proposed for general
plasma conditions.
Received 12 June 2001 and Received in final form 24 October 2001 相似文献
16.
A. Saffarzadeh 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):149-153
Spin-polarized tunneling in FMS/M/FMS double tunnel junctions where FMSs are ferromagnetic semiconductor layers and M is a
metal spacer is studied theoretically within the single-site coherent potential approximation (CPA). The exchange interaction
between a conduction electron and localized moment of the magnetic ion is treated in the framework of the s-f model. The spin polarization in the FMS layers is observed to oscillates as a function of the number of atomic planes in
the spacer layer. Amplitude of these oscillations decreases with increasing the exchange interaction in FMS layers.
Received 9 June 2001 and Received in final form 20 August 2001 相似文献
17.
P. Boubert P. Vervisch 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):43-48
Excitation of carbon monoxide molecules has been carried out in a cold cell and in a low-pressure plasma jet using an ArF
narrow-band excimer laser. The different excitation models are discussed and the relevance of atomic carbon absorption into
the laser cavities is pointed out. Excitation spectra of Cameron bands have been obtained in a room-temperature cell and compared
with calculated spectra. A value of the constant σ related to the interaction strength between a
3
Π(
v
= 2) state and its neighbouring singlet states is derived: 0≤σ≤0.05. The fluorescence spectrum following broad band excitation of CO has been observed both in UV and visible. Similar experiments
carried out in a high enthalpy flow have allowed to point out the presence of a
3
Π metastable carbon monoxide. A method for relative measurements of this species concentration is proposed.
Received 9 April 2001 and Received in final form 13 June 2001 相似文献
18.
E. Capobianco 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):201-211
We show new modeling aspects of stock return volatility processes, by first representing them through Hammerstein Systems,
and by then approximating the observed and transformed dynamics with wavelet-based atomic dictionaries. We thus propose an
hybrid statistical methodology for volatility approximation and non-parametric estimation, and aim to use the information
embedded in a bank of volatility sources obtained by decomposing the observed signal with multiresolution techniques. Scale
dependent information refers both to market activity inherent to different temporally aggregated trading horizons, and to
a variable degree of sparsity in representing the signal. A decomposition of the expansion coefficients in least dependent
coordinates is then implemented through Independent Component Analysis. Based on the described steps, the features of volatility
can be more effectively detected through global and greedy algorithms.
Received 31 December 2001 相似文献
19.
S. Pleutin A. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):521-531
The static polarizability of cylindrical systems is shown to have a strong dependence on a uniform magnetic field applied
parallel to the tube axis. This dependence is demonstrated by performing exact numerical diagonalizations of simple cylinders
(rolled square lattices), armchair and zig-zag carbon nanotubes (rolled honeycomb lattices) for different electron-fillings.
At low temperature, the polarizability as function of the magnetic field has a discontinuous character where plateau-like
region are separated by sudden jumps or peaks. A one to one correspondence is pointed out between each discontinuity of the
polarizability and the magnetic-field induced cross-over between the ground state and the first excited state. Our results
suggest the possibility to use measurements of the static polarizability under magnetic field to get important informations
about excited states of cylindrical systems such as carbon nanotubes.
Received 29 March 2001 and Received in final form 8 August 2001 相似文献
20.
T. Fritioff C. Carlberg G. Douysset R. Schuch I. Bergström 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):141-143
The atomic and nuclear masses of 4He and 3He have been measured using doubly charged ions in a Penning trap connected to an electron beam ion source. Recent technical
improvements allow mass determinations with uncertainties of a few parts in 1010. The obtained atomic masses are 4.002 603 256 8(13) u and 3.016 029 323 5(28) u respectively. These values deviate by as
much as 5 standard deviations from the accepted values.
Received 23 October 2000 and Received in final form 6 February 2001 相似文献