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The periodic instanton method is used to study the decay rates of metastable ground state and excited states of the cubic potential. The imaginary part of the energy is calculated through the standard procedure in the path-integral scheme. A formula of the decay rate valid for the entire region of energy is obtained. This formula provides a linkage between classical thermal activation at high temperatures and purely quantum tunneling at zero temperature. It is shown that in the low energy limit this more general result reduces exactly to the vacuum result. The temperature dependence of the decay rate agrees with earlier works in the literature. 相似文献
84.
We investigate the quantum transmission properties of connected multi-rings with impurities and analyse the effect of the impurities on the band formation in these geometric structures. It is shown that energy bands and band gaps are formed clearly while there is not any fixed band structure for the case of the single ring. The number of resonant peaks in conductance bands increases with the number of rings. Some essential differences are pointed out and magnetic properties of loop configurations in the presence of Aharonov-Bohm flux are explored as well. 相似文献
85.
In this paper, we investigate the condensate fraction (CF) of fermionic pairs in the BCS-BEC crossover for three- component Fermi gas with both asymmetric interactions and unequal chemical potentials in two-dimensional free space. By using the functional-path-integral method, we have analytically derived the number densities and bound-state energy, from which the off-diagonal long-range order is analyzed in terms of the asymptotic behavior of the two-body density matrix. The explicit formula of CF is obtained as a function of the bound-state energy and population imbalance. It is demonstrated that the CF spectrum with respect to the bound-state energy can be used to characterize the quantum phase transition between the two kinds of Sarma phases as well as the transition from three-component to two-component superfluid. Moreover we obtain the same analytic formula of CF in the BCS superfluid phase as that of homogeneous Fermi gas with equal chemical potentials. 相似文献
86.
本文给出谐振子包含极点和超越极点的扩展Feynman传播子公式的新推导。我们应用了传播子的本征函数展开,从而揭示出Maslov修正和本征函数字称的关系。这一扩展的 Feynman公式被用来讨论在稳恒均匀磁场中和有Chern-Simon背景规范场存在时迴旋运动带电粒子Feynman传播子位相修正及其物理效应。 相似文献
87.
本文从实验和理论方面研究了光栅吸收与入射激光的偏振取向和波长的关系.从计算模型得出的理论结果与观察值相符. 相似文献
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89.
Atomistic simulation of fcc-bcc phase transition in single crystal Al under uniform compression
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By molecular dynamics simulations employing an embedded atom model potential,we investigate the fcc-to-bcc phase transition in single crystal Al,caused by uniform compression.Results show that the fcc structure is unstable when the pressure is over 250 GPa,in reasonable agreement with the calculated value through the density functional theory.The morphology evolution of the structural transition and the corresponding transition mechanism are analysed in detail.The bcc (011) planes are transited from the fcc (11) plane and the (11) plane.We suggest that the transition mechanism consists mainly of compression,shear,slid and rotation of the lattice.In addition,our radial distribution function analysis explicitly indicates the phase transition of Al from fcc phase to bcc structure. 相似文献
90.
The ultracold polar molecules with the tunable dipole-dipole interaction, not only would enable explorations of a large class of exotic many-body physics phenomena, but also could be used for quantum information processing. In the present paper we demonstrate that this dipole-dipole interaction can generate the degenerate chiral quantum states acting as a qubit robust against noise when the ultracold polar molecules are confined by a triangular lattice. Moreover, we also find two first-order quantum phase transitions by controlling an external driving field. One is the transition with the change of the different degenerate chiral quantum states. The other is the transition with the breaking of the degenerate quantum chiral states to the nondegenerate state. In experiment, these first-order quantum phase transitions can be detected by measuring the collective molecular population. 相似文献