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Quantum dense coding properties between two identical and spatially separated atoms in free space with different initial states is investigated. It shows that dense coding capacity χ experienced a sharp decline firstly and then gradually increased to be one steady value 1 with increasing Γt. The realization of dense coding capacity χ is found to be strongly dependent on the initial states. It is worth noting that the initial pure state |ee〉 is not useful for dense coding in this system, due to the dense coding capacity χ is always less than 1(a valid dense coding capacity satisfies χ > 1). Otherwise, for the initial entangled state and mixed state, one can obtain the valid dense coding capacity, the results show that one threshold value of tc is exists, and when t < tc the dense coding capacity is valid. Tuning the atomic distance between the two atoms slightly broaden the valid dense coding region and improve the value of tc. Decreasing the purity a of initial states not only broaden the region but also prolong the effective time where one can carry out the valid dense coding successfully.

Optimal dense coding of a two-qubit anisotropic Heisenberg XXZ model under decoherence is investigated with the Werner state as the initial state. With the time evolution, the dense coding capacity χ oscillates firstly, and then reaches a stable value 1 in the long time limit, whatever the values of other parameters are. Our results imply that the purity r of the initial state have a strong influence on the initial value of the optimal dense coding capacity. When the purity r of the initial state increase, the initial value of dense coding capacity increase. Besides, the coupling coefficient and Dzyaloshinski-Moriya(DM) both have strong influence on the frequency of the oscillation and the area of t that the optimal dense coding is feasible(tf). Interestingly, the decoherence rate γ can strongly affect the dense coding capacity. With the decreasing of γ, the area of tf(which will make the dense coding capacity greater than 1) becomes more wider. When γ = 0, it will still allows a valid dense coding. So we can adjust the parameters to get a optimal dense coding.

We investigate the effects of spin squeezing interaction, external magnetic field and temperature on dense coding capacity properties in two kinds of two-qubit spin squeezing model: one-axis twisting model (OATM) and two-axis countertwisting model (TACM). To the OATM, it is found that the value of dense coding capacity χ is larger than 1 in the region of larger values of Ω(external magnetic filed) and μ(squeezing interaction) parameters space, while in the region of lower values of Ω and μ parameters space, χ is always less than 1 and not valid for dense coding. With increasing temperature T the dense coding capacity is decayed, and one can carry out the valid dense coding in the lower T region through tuning Ω. To the TACM, it is found that the value of χ is promoted with increasing the squeezing parameter γ. Through increasing γ, χ finally reached to one stable value, which is always larger than 1 whatever value of Ω is. The valid dense coding capacity χ can be enhanced through tuning the parameter Ω or γ, but it is decreased with increasing T. Our results show that with proper enhancing the parameter Ω or γ it is easy to carry out the valid dense coding (χ > 1) and the optimal dense coding (χ = 2) when the system in TACM.

We present numerical simulations on the correlated two-electron momentum distributions for the recollisional ($e, 2e$) process in nonsequential double ionization (NSDI) of helium by an 800-nm laser field at an intensity around $4.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.16em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$, based on the improved quantitative rescattering model, in which the lowering of the kinetic energy required for the electrons to escape from the parent ion due to the presence of electric field at the time of recollision has been taken into account. According to the QRS model, the correlated two-electron momentum distributions for laser-induced ($e, 2e$) collision in NSDI can be factorized as a product of the returning-electron wave packet (RWP) and the field-free differential cross section (DCS) for ionization of the parent ion by the impact of the laser-induced returning electron. The RWPs which describe the momentum distribution of the returning electrons are obtained within the strong-field approximation for high-order above threshold ionization. In the calculations of the DCSs for electron impact ionization of ${\mathrm{He}}^{+}$, the precollision Coulomb interaction between the incident electron and the parent ion and the postcollision Coulomb interaction between the two outgoing electrons are considered. In addition, the dynamic screening (DS) of the three-body Coulomb interactions in the final state, due to the fact that the strength of the interaction of any two particles is affected by the presence of the third one, has also been taken into account. It has been found that while the postcollision Coulomb interaction is responsible for the observed fingerlike structure, the precollision Coulomb interaction changes the orientation of the two fingers from $\mathsf{V}$-type to parallel, the final state DS reduces the separation of the two fingers, and the lowering of threshold energy shifts the two fingers towards smaller momenta. All these effects improve the agreement of the simulated results with the experimental results.

We present fully differential cross sections (FDCS) within three-body distorted wave (3DW) for the single ionization of He by 3.6 MeV/amu AuQ+ (Q=24, 53) ions. By comparing our calculations with experimental data and other theoretical predictions, we find the cross sections are strongly influenced by highly charged projectile, ejected electron would be “pulled” along in the forward direction. However, all of the theoretical approaches can not display experimental unique forward peak structures in the FDCS.

A pump-probe scheme for monitoring the electron dynamics of the excited state has been investigated by numerically solving the two-state time-dependent Schrödinger equation based on the non-Born-Oppenheimer approximation. By adjusting the delay time between a mid-infrared probe pulse and an ultra violet pump pulse, an obvious minimum can be seen in the higher-order harmonic region. With electron probability density distribution, ionization rate and classical simulation, the minimum can be ascribed to the electron localization around one nucleus at larger delay time and represents the electron dynamics of the excited state at the time of ionization. Moreover, the position of the minimum is much more sensitive to the nuclear motion.

The four-body model has been used to calculate the fully differential cross-sections (FDCS) for the single ionization of helium by 100 MeV/amu C6+ impact in geometries. By comparing with experimental data and other theories, we find the results of four-body model are in very good agreement in the scattering plane, but poor agreement out of the scattering plane. Accordingly, the contributions of different scattering amplitudes to FDCS are analyzed. It is found that the cross sections due to the interference of the scattering amplitudes between projectile-target nucleus interaction and projectile-ejected electron interaction almost tend to experimental results around the recoil region in geometries. In particular in the perpendicular plane, the cross section originating from interference of the scattering amplitudes between projectile-target nucleus and projectile-ejected electron interactions yields an experimental double-peak structure in the angular distribution. However, this feature could not be presented by the interference of the three amplitudes. Thus, the failure of the four-body model predicting the feature in this geometry may be attributed to an inappropriate weighting of the three amplitudes.

Three‐Coulomb‐wave method is employed to treat the process of (e, 2e) simultaneous ionization and excitation to the n=2 state of helium, with radial and angular correlated wave‐function of He target. The triple differential cross sections are calculated and analyzed in very asymmetric coplanar geometry at incident energies of 5.50, 1.50 and 0.57 keV. Results are compared with the absolute measurements and the theoretical first and second Born approximation. The present triply differential cross section (TDCS) is found to be in good agreement with experimental data qualitatively. The distinguishing feature noted in TDCS structure is the presence of intense recoil peak that for certain parameters is even larger than the binary peak, an unusual feature for the single‐ionization process at high and intermediate energies.

We consider the influence of magnetic fields on the model of neutrino-dominated accretion flows (NDAFs) for gamma-ray bursts (GRBs) via the assumption that the accretion rate of the disc is totally caused by the torque of the Lorentz force, i.e. the magnetic braking of large-scale magnetic fields and magnetic viscosity of small-scale magnetic fields. We calculate the structure, composition, luminosity of neutrino emission and the Poynting flux, and the rate of mass loss driven by neutrino heating or launched centrifugally by large-scale magnetic fields, based on the physical condition of the magnetized NDAFs. It is shown that the magnetized disc is favourable to interpret the diverse prompt emissions as well as the X-ray flares observed in the early afterglow of GRBs.

The phenomenon of multiple rescatterings in the process of high-order harmonic generation from a helium atom with a long wavelength is investigated by solving the time-dependent Schrodinger equation and the classical equation of motion. The results present the rule of cutoff energies for the multirescattering events. What is more, the physical picture of the multiple rescatterings is built and the physical mechanism is revealed in detail. Further studies show that the multiple rescatterings can be manipulated effectively and the intra-cycle interference of multiple rescatterings is weakened simultaneously when the initial state is prepared in the superposition state. Additionally, the long quantum path is verified to play an important role in the multiple rescattering processes.

The molecular multiple rescattering processes have been theoretically investigated via solving the time-dependent Schrödinger equation. Not only has the physical model been established, but also the related rescatterings originating from recombination with parent nucleus and with neighboring nucleus have been distinguished. Moreover, it has shown that the rescatterings originating from recombination with parent nucleus are similar with those atomic rescatterings, while those rescatterings from recombination with neighboring nucleus both before and after reversing the direction of the laser field are more sensitive to the internuclear distance. With time-frequency distribution and classical electron dynamics, the underlying mechanisms are revealed.

Fully differential cross sections (FDCS) are calculated within a four-body model for single ionization of helium by C6+ impact at the incident energy of 100 MeV/a.u. (atomic unit). The results are compared with experimental data and other theoretical predictions. It is shown that our results are in very good agreement with experiment for three small momentum transfers in the scattering plane; however, some significant discrepancies are still present at the largest momentum transfer in both the scattering plane and the perpendicular plane. In actuality, the problem has not been explained by the theory during the last decade. Accordingly, the contributions of different scattering amplitudes to FDCS are analyzed. It is found that for the largest momentum transfer the cross section arising from a destructive interference of the three amplitudes is much smaller than the experimental data. However, the cross section due to the constructive interference of two scattering amplitudes between projectile—ionized electron interaction and projectile—passive electron interaction almost approaches the experimental data.