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1.
Dicke模型中的量子相变在三十多年前已被预言,该模型描述的是N个二能级原子与单模腔场集体耦合的系统.在标准Dicke模型的基础上加入原子光的非线性相互作用和含时外场驱动,使用含时幺正变换和Holstein-Primafoff变换方法从理论上推导出基态能量表达式.并且给出了丰富的相图,而且这些性质最近已有文献从实验上验证.本文主要呈现了非线性相互作用和外场驱动对量子相变的影响. 相似文献
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3.
Refractive processes in strong-field QED are pure quantum processes, which involve only external photons and the background electromagnetic field. We show analytically that such processes occurring in a plane-wave field and involving external real photons are all characterized by a surprisingly modest net exchange of energy and momentum with the laser field, corresponding to a few laser photons, even in the limit of ultra-relativistic laser intensities. We obtain this result by a direct calculation of the transition matrix element of an arbitrary refractive QED process and accounting exactly for the background plane-wave field. A simple physical explanation of this modest net exchange of laser photons is provided, based on the fact that the laser field couples with the external photons only indirectly through virtual electron–positron pairs. For stronger and stronger laser fields, the pairs cover a shorter and shorter distance before they annihilate again, such that the laser can transfer to them an energy corresponding to only a few photons. These results can be relevant for the future experiments aiming to test strong-field QED at present and next-generation facilities. 相似文献
4.
R. Kh. Gainutdinov A. A. Mutygullina M. A. Khamadeev 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(12):1661-1665
The problem of nonlocality of effective interaction of radiation field with a strong classical electromagnetic field has been investigated. The interaction operator allowing one to take into account the natural nonlocality of such a process is derived from the analysis of ordered diagrams of quantum electrodynamics. 相似文献
5.
R. Kh. Gainutdinov A. A. Mutygullina 《Bulletin of the Russian Academy of Sciences: Physics》2009,73(2):281-283
Radiative corrections to the energy levels of an atom interacting with a strong laser field have been investigated. A formula
for the Lamb shift of the laser-dressed states is derived, which makes it possible to calculate this shift with an error up
to α2.
Original Russian Text ? R.Kh. Gainutdinov, A.A. Mutygullina, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya
Fizicheskaya, 2009, Vol. 73, No. 2, pp. 292–293. 相似文献
6.
G. Bilalbegović 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,49(1):43-49
The first 52 fs of a time evolution of the electron density in OCS after an interaction with an intense sub 10 fs laser pulse
are studied using the time-dependent density functional theory. The nuclear motion in this linear trimer is simulated by the
classical molecular dynamics method. Laser fields of intensity 1013 W/cm2 and 1015 W/cm2 are used. Details of the laser induced changes of the structure, as well as the ionization rate are sensitive to the applied
field intensity and its polarization. It is found that under suitable conditions the OCS molecule bends soon after an interaction
with a laser pulse. A deviation from the linear geometry of up to 23.6° and charged ions of up to +3 are observed. The time
evolution of electric dipole moments and the time-dependent electron localization function (ELF) are also studied. 相似文献
7.
The elastic differential cross-section forē-Na scattering in the presence of non-resonant laser field is studied for the exchange ofℓ=0, 1, 2 photons. The undressed contribution is evaluated within the framework of the eikonal Born series approximation and
the effect of exchange is taken into account via the Ochkur approximation. The sodium atom has been treated in the frozen
core approximation with special attention to the effect of the dressing of the target by the laser field. The ‘dressing’ of
the target leads to quite an increase in the cross-section over the ‘undressed’ value near the forward direction for the exchange
of one or two photons. 相似文献
8.
Summary The energy absorption rate by a classical homogeneous plasma irradiated by a strong fluctuating laser field via inverse bremsstrahlung
is considered. A chaotic-field model is used and comparison is made with the fundamental model of a purely coherent field.
In the present analysis, the emphasis is put on the interplay between the laser field statistics and the plasma electron energy
distribution. Numerical calculations are concerned with the dependence of the energy absorption rates on laser intensity and
frequency. Laser intensity values up to 4.6\1015 W/cm2 are considered. The multiphoton structure of the energy absorption is analysed as well. Concerning the joint influence of
the radiation and particle statistics on the absorption rate, the basic result may be stated as follows. For situations where
the particle thermal velocityv
T
is larger than the oscillatory velocityv
0 imparted by the field (v
T
≥v
0, relatively weak field), the absorption rate is only weakly dependent on the field statistics. For situations, instead, whenv
0≫v
T
, which occurs for very high intensities, the reverse becomes true: now the initial particle velocity distribution plays the
modest role of a velocity spread of an electron beam oscillating atv
0. In general, for very high intensities (v
0≫v
T
), the energy absorption via bremsstrahlung becomes less effective because the high oscillatory velocityv
0 reduces the time available to electrons for the interaction with the ions, the third body which makes possible the exchange
for energy between electrons and a radiation field. We report also, for the first time, results on the Marcuse effect for
the case of a chaotic laser field, along with calculations of the absorption rate for a directed electron beam. 相似文献
9.
High-order harmonic generation in a two-color strong laser field with Bohmian trajectory theory
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We theoretically study the high-order harmonic generation(HHG) in a two-color laser field using the Bohmian mechanics. Our results show that, for the case of a weak second-color laser field, the simulation of the HHG with only one central Bohmian trajectory is in a good agreement with the ab initio time-dependent Schr o¨dinger equation(TDSE) results.In contrast, with the increase of the amplitude of the second-color laser field, the HHG spectra from the single central Bohmian trajectory deviate from the TDSE results more and more significantly. By analyzing the Bohmian trajectories,we find that the significant deviation is due to the fact that the central Bohmian trajectory leaves the core quickly in the two-color laser field with the breaking of inversion symmetry. Interestingly, we find that another Bohmian trajectory with different initial position, which keeps oscillating around the core, could qualitatively well reproduce the TDSE results. Furthermore, we study the HHG spectrum in a two-color laser field with inversion symmetry and find that the HHG spectrum in TDSE can be still well simulated with the central Bohmian trajectory. These results indicate that, similar to the case of one color laser field, the HHG spectra in a two-color laser field can be also reproduced with a single Bohmian trajectory,although the initial position of the trajectory is dependent on the symmetry of the laser field. Our work thus demonstrates that Bohmian trajectory theory can be used as a promising tool in investigating the HHG process in a two-color laser field. 相似文献
10.
R. González-Férez P. Schmelcher 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):189-199
We investigate the effects of a magnetic field with low to intermediate strength on several spectroscopic properties of the
sodium atom. A model potential is used to describe the core of sodium, reducing the study of the system to an effective one-particle
problem. All states with principal quantum numbers n = 3, 4, 5, 6 and 7 are studied and analysed. A grid of twenty values for the field strength in the complete regime B = 0 - 0.02 a.u. is employed. Ionisation energies, transition wavelengths and their dipole oscillator strengths are presented.
Received 5 November 2002 Published online 4 February 2003 相似文献
11.
Obulkasim Oluk Bai-Song Xie Muhmmad Ali Bake Sayipjamal Dulat 《Frontiers of Physics》2014,9(2):157-163
By solving the quantum Vlasov equation, electron positron pair production in a strong electric field with asymmetric laser pulses has been investigated. We consider three different situations of subcycle, cycle and supercycle laser pulses. It is found that in asymmetric laser pulse field, i.e.. when the pulse length of one rising or falling side is fixed while the pulse length of the other side is changed, the pair production rate and mnnber density can be significantly modified comparable to symmetric situation. For each ca,se of these three different cycle pulses, when one side pulse length is constant and the other side pulse length becomes shorter, i.e., the whole pulse is compressed, the more pairs can be produced than that in tile vice versa case, i.e., the whole pulse is elongated. In compressed pulse case there exists an optimum pulse length ratio of asylnmetric pulse lengths which makes the pair number density maximunn. Moreover, the created maximum pair number density by subcycle pulse is larger than that by cycle or/and supercycle pulse. In elongated pulse case, however, only for supercycle laser pulse the created pairs is enhanced and there exists also an optimum asymmetric pulse length ratio that maximizes the pair number density. On the other hand. surprisingly, in both cases of subcycle and cycle elongated laser pulses, the pair number density is monotonically decreasing as the asymmetry of pulse increases. 相似文献
12.
本文研究氢原子在会聚的线偏振强激光场中原子势的变化以及由此而引起的原子能级移位和波函数的空间扩展问题.结果表明,变化后的原子势等价于半径由外场决定而荷电量为核电荷的振荡球壳的势.在此势下,原子能级将变浅和分裂,波函数的空间分布将增大. 相似文献
13.
M. Morato J. O. Caceres A. Gonzalez Ureña 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(1):215-218
Deflection of a cold supersonic NO beam seeded in He has been observed when
these molecules interact with both static and a resonant oscillating electric field. The NO beam splits into two beams each
one deflecting about 0.5° towards the positive and negative direction of the Stark field when the employed resonant frequency
between the two Stark levels of the NO molecule is 1515 kHz. This deflection angle is about four orders of magnitude higher
than the value one would expect from the NO dipole moment and the employed RF field gradient. This phenomenon suggests the
possibility of a significant translational motion perpendicular to the beam axis, which is induced by the resonant RF electric
field on the cold and high-density supersonic beam. 相似文献
14.
E. A. Volkova A. M. Popov O. V. Tikhonova 《Journal of Experimental and Theoretical Physics》2001,93(6):1155-1162
The interaction of a three-dimensional atomic system in a short-range potential with intense laser radiation is investigated by the direct numerical integration of the nonstationary Schrödinger equation. The calculations helped to discover a stabilization regime, which is interpreted as a result of forming a Kramers-Henneberger atom “dressed” in a field. Dynamics of the energy spectrum of photoelectrons depending on the increase of the laser field intensity is investigated, and conditions of a photodetachment of an electron from a bound state of the Kramers-Henneberger potential are analyzed. These results reveal specific features of the stabilization process of the three-dimensional system with a short-range potential compared to the similar process in a system with a long-range (Coulomb) potential. 相似文献
15.
Y. Kimura Y. Kitahama K. Takazawa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(1):203-208
Experimental set-up for studying effects of a strong magnetic field on a structure and a decay dynamics of molecules, was
designed and constructed. A vacuum chamber, in which a molecular beam propagated, was mounted in a bore of a superconducting
magnet. Laser light crossed the molecular beam in the magnetic field and excited the molecules. Fragment or parent ions produced
through sequential decay processes, were extracted by an electric field parallel to the magnetic field and detected by a microchannel
plate. By measuring the time-of-flight from the photo-excitation to the ion-detection, a species of ions —mass and charge
state— was identified. A performance of the set-up was demonstrated using the resonance enhanced multiphoton ionization process
through the
X2Π-A2Σ+ transition of nitric oxide (NO) molecules. A mass resolution m/Δm ≥180±6 was obtained in the field up to 10 T. This was
the first successful result demonstrating the sufficient mass resolution obtained by the time-of-flight technique in the strong
magnetic field up to 10 T. Parent NO+ ions were selectively detected by the mass spectrometer and the ion current was measured as a function of the frequency of
the laser light. Rotational transition lines were measured with a sufficient S/N ratio in the field up to 10 T. 相似文献
16.
Quantum correlations in a two-qubit anisotropic Heisenberg XYZ chain with uniform magnetic field
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Quantum correlations in an anisotropic Heisenberg XY Z chain is investigated by use of concurrence C and measurement-induced disturbance(MID). We show that the behaviors of the MID are remarkably different from the concurrence. Firstly, it is shown that there is a revival phenomenon in the concurrence but not in the MID, which is suitable for both the ground state case and the finite temperature case. Based on the analysis of the ground-state C and MID structures,we illustrate the reason why the ground-state MID does not show a revival phenomenon in detail. Then we explore different effects of the external and self parameters on entanglement and MID behaviors. It can be shown that the region of MID is evidently larger than the case of concurrence, and that the concurrence signals a quantum phase transition even at finite T while MID does not. Cases where the concurrence finally maintains one nonzero constant value regardless of the value of the variable B for a constant Jz, while MID decreases monotonously to zero with increasing B. We also show that if B can take a proper range of values, the concurrence decreases with the improvement of the anisotropic parameter γ, whereas an opposite effect for MID behaviors is presented. 相似文献
17.
A gauge-invariant Green’s function approach to the quantum transport of spatially confined electrons in strong electromagnetic fields is presented. The theory includes mean field and exchange effects, as well as collisions and initial correlations. It allows for a self-consistent treatment of spectral properties and collective effects (plasmons), on one hand, and nonlinear field phenomena, such as harmonic generation and multiphoton absorption, on the other. It is equally applicable to electrons in quantum dots, ultracold ions in traps and valence electrons of metal clusters. 相似文献
18.
E. Hasovi? D. B. Milo?evi? M. Busulad?i? A. Gazibegovi?-Busulad?i? W. Becker 《Laser Physics》2012,22(12):1827-1832
The molecular strong-field approximation is applied to calculate angle-resolved photoelectron spectra in the process of high-order above-threshold ionization of carbon-monoxide molecules by an elliptically polarized laser field. The theory is formulated to include the Stark shift of the initial bound state of the valence electron. It is shown that the angle-resolved photoelectron spectra of aligned CO molecules exhibit pronounced minima which can be explained by destructive interference of two partial T-matrix contributions. The dependence of contributing partial amplitudes on the laser field ellipticity is analyzed in detail. 相似文献
19.
基于自由电子激光器的能量模型,在具有螺旋磁场自由电子激光器中,本文采用一种简单的方法处理了强信号条件下能量转换过程.讨论了饱和产生的过程和初始能量色散对饱和影响的机制.这种处理方法也适用于自由电子激光器的谐波辐射. 相似文献