Spin dynamics in Keldysh formalism

ERNESTO P. DANIELI; GONZALO A. ÁLVAREZ; HORACIO M. PASTAWSKI; PATRICIA R. LEVSTEIN

Miramare, Trieste, Italy

Conferencia; Third Stig Lundqvist Conference on Advancing Frontiers of Condensed Matter Physics: "Fundamental Interactions and Excitations in Confined Systems"; 2003

The Abdus Salam International Centre for Theoretical Physics (ICTP)

We formulate the many-body spin dynamics at high temperature within the non-equilibrium Keldysh formalism. For the simplest XY interaction, analytical expressions in terms of the one particle solutions are obtained for linear and ring configurations. We present the formalism applied to closed and open system. For the closed case we solve the dynamic of local excitations in small rings of even size, and obtain different group velocities for excitations in systems with different total spin projections. This should enable an experimental filtering of spin projections with a given parity i.e. a spin projection chromatography. On the other hand we solve the action of a spin bath over a two interacting spin system as an incoherent injection of quantum waves. We discuss the simplest case in this category: the problem of cross-polarization transfer in NMR in which the nuclear spin system 13C - 1H is in contact with a spin reservoir. For a solvable model of this system, the result of the Keldysh equation with a decoherent source is shown to give the exact dynamics. Comparison with other results are done.