WKB properties of the time-dependent Schrödinger system

Jeong Ryeol Choi

Jędrzej Śniatycki

Raphael N. P. Maia, F. Nicacio, Raúl O. Vallejos +1 more

We analyze the semiclassical evolution of Gaussian wave packets in chaotic systems. We show that after some short time a Gaussian wave packet becomes a primitive WKB state. From then on, the state can be propagated using the standard time-dependent WKB scheme. Complex trajectories are not necessary to account for the long-time propagation. The Wigner function of the evolving state develops the structure of a classical filament plus quantum oscillations, with phase and amplitude being determined by geometric properties of a classical manifold.

MASSIMO RUDAN

John E. G. Farina

Scattering by a one-dimensional potential V=V(x) which is constant outside (-a, a) (a>0) is investigated. Exact expressions for the transmission and reflection coefficients are obtained in terms of f 0 (a), f 1 (a), f' O (a) and f' 1 (a), where f 0 and f 1 are the solutions in (-a, a) satisfying the boundary conditions f 0 (-a)=1, f 0 '(-a)=0, f 1 (-a)=0 and f 1 '(-a)=1. These expressions are used to show that the first-order WKB approximation conserves particles. Numerical results are obtained from these expressions for the transmission and reflection probabilities by (i) using the WKB formulae and (ii) solving the time-independent Schrodinger equation numerically in (-a, a). The time T for the centre of a wavepacket to traverse the interval (-a, a) is also obtained in terms of f 0 (a), f 1 (a), f 0 '(a) and f 1 '(a), and some of its properties studied. In particular, it is shown that T takes the classical form in the classical limit.

C. F. Huang, Sheng Der Chao, Da‐Ren Hang +1 more

We have obtained a set of coupled differential equations from the continuous limit of the transfer matrix method. Decoupling such a set of equations yields an extension to the Wentzel-Kramers-Brillouin (WKB) approximation for the Schrödinger equation with the position-dependent effective mass (PDEM). In the classically allowed region, the decoupling is to ignore the reflection resulting from the variations of both the potential and effective mass. By considering an infinite-well example with the PDEM, it is shown that the extended WKB approximation can provide not only an estimation to eigenenergies, but also an analytic form to approximate wavefunctions.