分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： We perform a systematic study of capture excitation functions by using an empirical coupled-channel model. In this model, a barrier distribution is used to take effectively into account the effects of couplings between the relative motion and intrinsic degrees of freedom. The shape of the barrier distribution is of an asymmetric Gaussian form. The effect of neutron transfer channels is also included in the barrier distribution. Based on the interaction potential between the projectile and the target, empirical formulas are proposed to determine the parameters of the barrier distribution. Theoretical estimates for barrier distributions and calculated capture cross sections together with experimental cross sections of 220 reaction systems with 182 ZPZT 1640 are tabulated. The results show that our empirical formulas work quite well in the energy region around the Coulomb barrier. This model can provide prediction of capture cross sections for the synthesis of superheavy nuclei as well as valuable information on capture and fusion dynamics.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： Macroscopic parameters as well as precise information on the random force characterizing the Langevin type description of the nuclear fusion process around the Coulomb barrier are extracted from the microscopic dynamics of individual nucleons by exploiting the numerical simulation of the improved quantum molecular dynamics. It turns out that the dissipation dynamics of the relative motion between two fusing nuclei is caused by a non-Gaussian distribution of the random force. We find that the friction coefficient as well as the time correlation function of the random force takes particularly large values in a region a little bit inside of the Coulomb barrier. A clear non-Markovian effect is observed in the time correlation function of the random force. It is further shown that an emergent dynamics of the fusion process can be described by the generalized Langevin equation with memory effects by appropriately incorporating the microscopic information of individual nucleons through the random force and its time correlation function.
分类： 物理学 >> 核物理学 提交时间： 2017-07-30
摘要： Applying a macroscopic reduction procedure on the improved quantum molecular dynamics (ImQMD) model, the energy dependences of the nucleus-nucleus potential, the friction parameter, and the random force characterizing a one-dimensional Langevin-type description of the heavy-ion fusion process are investigated. Systematic calculations with the ImQMD model show that the fluctuation-dissipation relation found in the symmetric head-on fusion reactions at energies just above the Coulomb barrier fades out when the incident energy increases. It turns out that this dynamical change with increasing incident energy is caused by a specific behavior of the friction parameter which directly depends on the microscopic dynamical process, i.e., on how the collective energy of the relative motion is transferred into the intrinsic excitation energy. It is shown micro- scopically that the energy dissipation in the fusion process is governed by two mechanisms: One is caused by the nucleon exchanges between two fusing nuclei, and the other is due to a rearrangement of nucleons in the intrinsic system. The former mechanism monotonically increases the dissipative energy and shows a weak dependence on the incident energy, while the latter depends on both the relative distance between two fusing nuclei and the incident energy. It is shown that the latter mechanism is responsible for the energy dependence of the fusion potential and explains the fading out of the fluctuation-dissipation relation.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Zheng-Hao Liu
Yu Meng
Yu-Ze Wu
Ze-Yan Hao
Zhen-Peng Xu
Cheng-Jun Ai
Hai Wei
Kai Wen
Jing-Ling Chen
Jie Ma
Jin-Shi Xu
Chuan-Feng Li
Guang-Can Guo
摘要： Contextuality, a hallmark feature of the quantum theory, captures the incompatibility between quantum correlations and any noncontextual hidden-variable model. The Greenberger--Horne--Zeilinger (GHZ)-type paradoxes are proofs of contextuality which reveal this incompatibility with deterministic logical arguments. However, the simplest GHZ-type paradox with the fewest number of complete contexts and the largest degree of nonclassicality remains elusive. Here, we derive a GHZ-type paradox utilising only three complete contexts and show this number cannot be further reduced. We forward to demonstrating the paradox with an experiment which recovered all essential ingredients in a 37-dimensional contextuality test based on high-speed modulation, optical convolution and homodyne detection of time-multiplexed modes of coherent light that can be interpreted as a classical entity. By proposing and observing a strong form of contextuality in an extremely high-dimensional system, our results pave the way for the exploration of exotic quantum correlations with optical systems.
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