arXiv subjects

Jie Liu

Publications and source records attributed to Jie Liu.

767 records · Page 43Linked to original sources

arXiv2001

Classical collisional trajectories as the source of strong-field double ionization of helium in the knee regime

In this paper, a quasistatic model is extended to describe the double ionization of Helium in intense linearly polarized field, yielding achieve an insight to the two-electron correlation effect in the ionization dynamics. Our numerical calculations reproduce the excessive double ionization and the photoelectron spectra observed experimentally both quantitatively and qualitatively. Moreover, it is shown that the classical collisional trajectories are the main source of the double ionization in the knee regime and responsible for the unusual angular distribution of the photoelectrons.

physics.atom-ph↗

arXiv2001

Quantum Step Heights in Hysteresis Loops of Molecular Magnets

We present an analytical theory on the heights of the quantum steps observed in the hysteresis loops of molecular magnets. By considering the dipolar interaction between molecular spins, our theory successfully yields the step heights measured in experiments, and reveals a scaling law for the dependence of the heights on the sweeping rates hidden in the experiment data on Fe$_8$ and Mn$_4$. With this theory, we show how to accurately determine the tunnel splitting of a single molecular spin from the step heights.

cond-mat.soft↗

arXiv2001

Theory of nonlinear Landau-Zener tunneling

A nonlinear Landau-Zener model was proposed recently to describe, among a number of applications, the nonadiabatic transition of a Bose-Einstein condensate between Bloch bands. Numerical analysis revealed a striking phenomenon that tunneling occurs even in the adiabatic limit as the nonlinear parameter $C$ is above a critical value equal to the gap $V$ of avoided crossing of the two levels. In this paper, we present analytical results that give quantitative account of the breakdown of adiabaticity by mapping this quantum nonlinear model into a classical Josephson Hamiltonian. In the critical region, we find a power-law scaling of the nonadiabatic transition probability as a function of $C/V-1$ and $α$, the crossing rate of the energy levels. In the subcritical regime, the transition probability still follows an exponential law but with the exponent changed by the nonlinear effect. For $C/V>>1$, we find a near unit probability for the transition between the adiabatic levels for all values of the crossing rate.

quant-ph↗

arXiv2001

Controlled Generation of Dark Solitons with Phase Imprinting

The generation of dark solitons in Bose-Einstein condensates with phase imprinting is studied by mapping it into the classic problem of a damped driven pendulum. We provide simple but powerful schemes of designing the phase imprint for various desired outcomes. We derive a formula for the number of dark solitons generated by a given phase step, and also obtain results which explain experimental observations.

cond-mat↗

arXiv1999

Quantum chaos of a kicked particle in a 1D infinite square potential well

We study quantum chaos in a non-KAM system, i.e. a kicked particle in a one-dimensional infinite square potential well. Within the perturbative regime the classical phase space displays stochastic web structures, and the diffusion coefficient D in the regime increases with the perturbative strength K giving a scaling $D \propto K^{2.5}$, and in the large K regime D goes as K^2. Quantum mechanically, we observe that the level spacing statistics of the quasi eigenenergies changes from Poisson to Wigner distribution as the kick strength increases. The quasi eigenstates show power-law localization in the small K region, which become extended one at large K. Possible experimental realization of this model is also discussed.

chao-dyn↗

arXiv1998

Nonadiabatic Geometric Phase and Hannay Angle: A Squeezed State Approach

The geometric phases of the cyclic states of a generalized harmonic oscillator with nonadiabatic time-periodic parameters are discussed in the framework of squeezed state. A class of cyclic states are expressed as a superposition of an infinte number of squeezed states. Then, their geometric phases are obtained explicitly and found to be $-(n+1/2)$ times the classical nonadiabatic Hannay angle. It is shown that the analysis based on squeezed state approach provide a clear picture of the geometric meaning of the quantal phase.

cond-mat↗

arXiv1998

Nonadiabatic geometric phase for the cyclic evolution of a time-dependent Hamiltonian system

The geometric phases of the cyclic states of a generalized harmonic oscillator with nonadiabatic time-periodic parameters are discussed in the framework of squeezed state. It is shown that the cyclic and quasicyclic squeezed states correspond to the periodic and quasiperiodic solutions of an effective Hamiltonian defined on an extended phase space, respectively. The geometric phase of the cyclic squeezed state is found to be a phase-space area swept out by a periodic orbit. Furthermore, a class of cyclic states are expressed as a superposition of an infinte number of squeezed states. Their geometric phases are found to be independent of $\hbar$, and equal to $-(n+1/2)$ times the classical nonadiabatic Hannay angle.

quant-ph↗

arXiv1998

Squeezed state dynamics of kicked quantum systems

We study kicked quantum systems by using the squeezed state approach. Taking the kicked quantum harmonic oscillator as an example, we demonstrate that chaos in an underlying classical system can be enhanced as well as suppressed by quantum fluctuations. Three different energy diffusions are observed in the kicked quantum harmonic oscillator, namely, localization, linear diffusion, and quadratic diffusion.

chao-dyn↗

arXiv1998

Quantum fluctuations: Enhancement or suppression of chaos?

We have studied the effects of quantum fluctuations on dynamical behavior by using squeezed state approach. Our numerical results of the kicked harmonic oscillator demonstrate qualitatively and quantitatively that quantum fluctuations can not only enhance chaos but also suppress classical diffusion. In addition, the squeezed state approach also gives a simple picture of dynamical localization.

chao-dyn↗

arXiv1998

Plateau in Above-Threshold-Ionization Spectra and Chaotic Behavior in Rescattering Process

An improved quasistatic model is used to describe the ionization process of atoms in intense linearly polarized fields. Numerical calculations of Above-Threshold-Ionization (ATI) energy spectra and photoelectron angular distributions (PAD) of hydrogen atoms reveal clearly plateau and side lobe structures, which are in good agreement with recent ATI experiments. Our results show that, the existence of this plateau and side lobes is consequences of the classical kinematics of the electrons in combined atom and laser fields. Furthermore, we find that the onset of these unusual phenomena is related to the onset of the chaotic behavior in the system.

chao-dyn↗

arXiv1998

Chaotic Behavior of a One-dimensional Model Atom in an Intense Field

In this paper we describe the rescattering process in optical field ionization through a one-dimensional model, which improves the well-known quasistatic model by adding the smoothed Coulomb potential in its second step. The above-threshold ionization spectra and high-order harmonic generation are calculated from this model. They are qualitatively in agreement with the quantum results and experiments. In particular, we find that this model is characterized by chaotic scattering. Modern nonlinear theory is used to analyze this dynamical system. It is found that singular self-similar fractal structure exists in the phase-dependence energy spectra, and the unstable manifolds constitute the chaotic scattering pattern. Our results also demonstrate a close connection of irregular trajectories with the energy spectra and high-order harmonic generation. We conclude that the chaotic behavior plays an important role in this one-dimensional model of optical field ionization.

chao-dyn↗