Artículos de revistas
Semiclassical Approximations Based On Complex Trajectories.
Registro en:
Physical Review. E, Statistical, Nonlinear, And Soft Matter Physics. v. 69, n. 6 Pt 2, p. 066204, 2004-Jun.
1539-3755
15244705
Autor
Ribeiro, A D
de Aguiar, M A M
Baranger, M
Institución
Resumen
The semiclassical limit of the coherent state propagator <z absolute value of e(-i H T/Planck's over 2 pi) z'> involves complex classical trajectories of the Hamiltonian H(u,v) = <v absolute value of H u> satisfying u(0) = z' and v(T) = z*. In this work we study mostly the case z' = z. The propagator is then the return probability amplitude of a wave packet. We show that a plot of the exact return probability brings out the quantal images of the classical periodic orbits. Then we compare the exact return probability with its semiclassical approximation for a soft chaotic system with two degrees of freedom. We find two situations where classical trajectories satisfying the correct boundary conditions must be excluded from the semiclassical formula. The first occurs when the contribution of the trajectory to the propagator becomes exponentially large as Planck's over 2 pi goes to zero. The second occurs when the contributing trajectories undergo bifurcations. Close to the bifurcation the semiclassical formula diverges. More interestingly, in the example studied, after the bifurcation, where more than one trajectory satisfying the boundary conditions exist, only one of them in fact contributes to the semiclassical formula, a phenomenon closely related to Stokes lines. When the contributions of these trajectories are filtered out, the semiclassical results show excellent agreement with the exact calculations. 69 066204