Browsing by Author "Jiang, Tsin-Fu"

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A Dynamical Decomposition of the Hamiltonian for Analyzing the Time Evolution of Quantum Mechanically Driven Harmonic Oscillator Systems
(2015-12-01)
Lin, Chyi-Lung
;
Jiang, Tsin-Fu
;
物理研究所
;
Institute of Physics
For analyzing the time evolution of quantum mechanically driven harmonic oscillator systems, we first establish the eigenvalue equation for the time-evolved wave function, and then we dynamically decompose the Hamiltonian into two parts. One part is the operator which does not change the state, and the other part does. Through this decomposition, the time evolution of the state can be solved more easily than in the familiar way. We illustrate this method by exactly solving the system of the driven harmonic oscillator. We show that nonspreading wave packets can also exist in this system in addition to the historically known paradigms, the profiles of which are the same as those in the harmonic oscillator system.
A Dynamical Decomposition of the Hamiltonian for Analyzing the Time Evolution of Quantum Mechanically Driven Harmonic Oscillator Systems
(2015-12)
Lin, Chyi-Lung
;
Jiang, Tsin-Fu
;
物理研究所
;
Institute of Physics
For analyzing the time evolution of quantum mechanically driven harmonic oscillator systems, we first establish the eigenvalue equation for the time-evolved wave function, and then we dynamically decompose the Hamiltonian into two parts. One part is the operator which does not change the state, and the other part does. Through this decomposition, the time evolution of the state can be solved more easily than in the familiar way. We illustrate this method by exactly solving the system of the driven harmonic oscillator. We show that nonspreading wave packets can also exist in this system in addition to the historically known paradigms, the profiles of which are the same as those in the harmonic oscillator system.
Band structures of a dipolar Bose-Einstein condensate in one-dimensional lattices
(2008-08-01)
Lin, YuanYao
;
Lee, Ray-Kuang
;
Kao, Yee-Mou
;
Jiang, Tsin-Fu
;
物理研究所
We derive the effective Gross-Pitaevskii equation for a cigar-shaped dipolar Bose-Einstein condensate in one-dimensional lattices and investigate the band structures numerically. Due to the anisotropic and the long-ranged dipole-dipole interaction in addition to the known contact interaction, we elucidate the possibility of modifying the band structures by changing the alignment of the dipoles with the axial direction. With the considerations of the transverse parts and the practical physical parameters of a cigar-shaped trap, we show the possibility to stabilize an attractive condensate simply by adjusting the orientation angle of dipoles. Some interesting Bloch waves at several particle current densities are identified for possible experimental observations.
Effects of strong laser fields on hadronic helium atoms
(2015-12-30)
Lee, Han-Chieh
;
Jiang, Tsin-Fu
;
物理研究所
;
Institute of Physics
The metastable hadronic helium atoms in microseconds lifetime are available in laboratory, and two-photon spectroscopy was reported recently. This exotic helium atom has an electron in the ground state and a negative hadron rotating around the helium nucleus. We theoretically study the excitation on hadronic helium by femtosecond pulse and elucidate the influence of moleculelike structure and rotation behavior on the photoelectron spectra and high-order harmonic generation. Because of the moleculelike structure, the electronic ground state consists of several angular orbitals. These angular orbitals can enhance photoelectron spectra at high energies, and also influence the harmonic generation spectra considerably. In particular, the harmonic spectra can occur at even harmonic orders because of the transition between these angular orbitals and continuum states. On the other side, the rotation behavior of hadron can induce a frequency shift in the harmonic spectra. The magnitude of the frequency shift depends on the orbiting speed of the hadron, which is considerable because the rotation period is in a few femtoseconds, a time scale that is comparable to that of infrared laser and is feasible in current laser experiments.
Lande subtraction method with finite integration limits and application to strong-field problems
(2012-12-11)
Jiang, Tsin-Fu
;
Jheng, Shih-Da
;
Lee, Yun-Min
;
Su, Zheng-Yao
;
物理研究所
The Lande subtraction method has been widely used in Coulomb problems, but the momentum coordinate p is an element of (0,infinity) is assumed. In past applications, a very large range of p was used for accuracy. We derive the supplementary formulation with p is an element of (0, p(max)) at reasonably small p(max) for practical calculations. With the recipe, accuracy of the hydrogenic eigenspectrum is dramatically improved compared to the ordinary Lande formula by the same momentum grids. We apply the present formulation to strong-field atomic above-threshold ionization and high-order harmonic generations. We demonstrate that the proposed momentum space method can be another practical theoretical tool for atomic strong-field problems in addition to the existing methods. DOI:10.1103/PhysRevE.86.066702
Magnetic quantum number dependence of hydrogen photoelectron spectra under circularly polarized pulse in barrier suppression ionization regime
(2018-08-01)
Jheng, Shih-Da
;
Jiang, Tsin-Fu
;
Chen, Jen-Hao
;
Liu, Jinn-Liang
;
物理研究所
Photoelectron spectra and transition mechanisms of a hydrogen atom in the n = 2 state under circularly polarized pulses in the barrier suppression ionization (BSI) regime, found by solving the time-dependent Schrodinger equation, are presented in detail. The photoelectron peak emerges from low-energy, in contrast to being centered at higher energy in the case of ionization from the ground state. We show that the magnetic quantum number dependence of photoelectron angular distributions on initial states yields 3- and 2-band structures for 2p(-) and 2p(0) in zenith angle, respectively, and 1-band structures for both 2p(+) and 2s. The intermediate transition pathways from these initial states to the corresponding final states are also revealed.
Nonlinear optics of graphene in the presence of Rabi oscillation
(2014-10-01)
Lee, Han-Chieh
;
Jiang, Tsin-Fu
;
物理研究所
;
Institute of Physics
When graphene is subjected to a strong light field, its nonlinear optical response allows only odd harmonic emissions because of a centrosymmetric structure. We demonstrate that this limitation no longer holds when the generation of an electric current density is considered within a quantum theory because of the involvement of the Rabi oscillation in the nonlinear optical response. By transforming the time-dependent Dirac equation into the length gauge, the Rabi frequency in graphene can be defined, allowing the identification of the Rabi coupling effect on the current-induced harmonic spectra. In particular, a peak at the spectral position of the second harmonic of the incident light can be generated in graphene when the intensity of the incident light causes the Rabi frequency to become comparable with the frequency of the incident light, which was demonstrated in ZnO with a measurement of carrier-envelope-offset frequency [Phys. Rev. Lett. 90, 217404 (2003)]. Moreover, as the light intensity increases, we show that a broadband harmonic spectrum is generated and that a compact electron distribution caused by multiphoton absorptions is produced because of highly nonlinear effects associated with the Rabi oscillation. (C) 2014 Optical Society of America
Study of the circular dichroism of He+ ion
(2019-12-01)
Chen, Jen-Hao
;
Liu, Jinn-Liang
;
Jheng, Shih-Da
;
Cheng, Szu-Cheng
;
Jiang, Tsin-Fu
We study the mechanism of circular dichroism (CD) in He+ under XUV and NIR pulses in the experimental condition presented by Ilchen et al. [Phys. Rev. Lett. 118, 013002 (2017)] and in a range of pulse intensities and durations by solving the time-dependent Schrodinger equation (TDSE) in momentum space. The method enables investigation of the ionization and intermediate transition probabilities of He+ in detail. We show that the lowest-order perturbation theory (LOPT) is qualitatively sufficient to describe experimental results and find that ionization favors co- and counter-rotating pulses for NIR intensities in and beyond LOPT regimes, respectively. In the experimental pulse duration, we show that a sub-peak along the first above-threshold ionization peak exists in the counter-rotating case due to one-photon absorption from excited states, which cannot be obtained by solving TDSE with a short duration of 22 fs, since the energy band width is too wide to resolve this substructure. We present the variation of CD values with NIR intensities. (C) 2019 Optical Society of America
Time evolution of freely expanded Bose-Einstein condensates containing small numbers of atoms
(2007-04-01)
Hong, De-Sheng
;
Huang, K. H.
;
Jiang, Tsin-Fu
;
Han, D. J.
;
物理研究所
We investigate the time evolution of freely expanded Bose-Einstein condensates by measuring their aspect ratios at different times after their release from a magnetic trap. In these measurements the condensates contain no more than 9000 Rb-87 atoms. By varying the trapping frequency and atom number, we measure the condensate aspect ratios at different expansion times in free space. We compare our measurements with those calculated from the Thomas-Fermi model and a direct numerical solution. Under our trapping condition, the data of the time dependent aspect ratios of the freely expanded condensates reasonably agrees with the numerical calculations, but shows a clear deviation from the predictions of the Thomas-Fermi model when the atom number in the condensates is small.