Thermalization and decoherence through stroboscopic measurements and injections. Application to a spin system

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

Córdoba, Argentina

Taller; 2º Taller Regional de Física Estadística y sus Aplicaciones a la Física de la Materia Condensada (TREFEMAC'04); 2004

A model for the quantum dynamics of two coupled spins with one of them connected to a reservoir is developed. The influence of the environment is simulated by stroboscopically (and then continuously) stopping the quantum evolution of the two-spin system, which in this way loses coherence. Polarization is injected to the system at each step of the interrupted evolution with certain probability. Excellent agreement with NMR experiments taken in molecular crystals is observed. It is remarkable that this simple model produces the exact result that can be obtained by reintroducing the neglected non-secular terms in the generalized Liouville-von Neumann approach introduced by Müller et al. [Phys. Rev. Lett. 32 (1974) 1402]. Moreover, it contains the quantum dynamics for short time and the Quantum Zeno Effect is evidenced. Hence, it is possible to establish the equivalence between these approaches improving our understanding of the effects of different interactions on the evolution, i.e., those that produce dissipation and those that only induce decoherence. This model contains unitary evolution using the propagators of the system without the necessity of including the bath. The bath participates stroboscopically and instantaneously, so it is very simple to apply in an algorithm and it converge easily to the continuous form.