Time-Dependent Quantum Mechanical Problems Solvable by Contour Integration

Yu. N. Demkov, Vladimir I. Osherov

Ricardo Cordero–Soto

Kálmán Varga, Joseph A. Driscoll

Jeremy Canfield, Anna Galler, James K. Freericks

Quantum mechanics has about a dozen exactly solvable potentials. Normally, the time-independent Schrödinger equation for them is solved by using a generalized series solution for the bound states (using the Fröbenius method) and then an analytic continuation for the continuum states (if present). In this work, we present an alternative way to solve these problems, based on the Laplace method. This technique uses a similar procedure for the bound states and for the continuum states. It was originally used by Schrödinger when he solved the wave functions of hydrogen. Dirac advocated using this method too. We discuss why it is a powerful approach to solve all problems whose wave functions are represented in terms of confluent hypergeometric functions, especially for the continuum solutions, which can be determined by an easy-to-program contour integral.

James K. Freericks, Volodymyr Turkowski, V. Zlatić

Nonequilibrium quantum mechanics can be solved with the Keldysh formalism, which evolves the quantum mechanical states forward in time in the presence of a time-dependent field, and then evolves them backward in time, undoing the effect of the time-dependent field. The Feynman path integral over the Keldysh contour is employed to calculate the strongly correlated Green's function. We examine the accuracy of this procedure for the simplest problem that requires a nonequilibrium formulation: the electron spectral function of the spinless Falicov-Kimball model.

R. Németh, József Cserti

We develop a unified treatment of the non-Abelian Aharonov-Bohm (AB) effect in isotropic multiband systems, namely, the scattering of particles on a gauge field corresponding to a noncommutative Lie group. We present a complex contour integral representation of the scattering states for such systems, and using their asymptotic form, we calculate the differential scattering cross section. The angular dependence of the cross section turns out to be the same as that obtained originally by Aharonov and Bohm in their seminal paper [Phys. Rev. 115, 485 (1959)], but this time, it depends on the polarization of the incoming plane wave. As an application of our theory, we perform the contour integrals for the wave functions explicitly and calculate the corresponding cross section for three nontrivial isotropic multiband systems relevant to condensed matter and particle physics. To have a deeper insight into the nature of the scattering, we plot the probability and current distributions for different incoming waves. This paper is a generalization of our recent results on the Abelian AB effect providing an extension of exactly solvable AB scattering problems.