| In recent years the study of shot noise in mesoscopic quantum systems has become an emerging topic in mesoscopic physics, because a measurement of shot noise can reveal more information of transport properties which is not available through the conductance measurement alone [1, 2].; Besides, special interest has recently been put on the investigation of tunneling through a two-level system (TLS), when the coherent coupling between the two levels is presented. It is quite desirable to find a way of evaluating current correlation in arbitrary bias-voltages, particularly in moderately small bias-voltage region, where the coherence plays a more prominent role in quantum tunneling processes. Accordingly, the purpose of this work is to develop a general scheme to study the quantum shot noise spectrum of coupled small quantum systems based on the recently established quantum rate equations with a bias-voltage and temperature dependent version [22].; Actually, a numerical method, named generation-recombination approach, was established for analysis of shot noise in two-terminal single-electron tunneling devices with the classical rate equation (classical shot noise) in Refs. [23, 24, 25]. These earlier papers proposed a powerful method to evaluate the double-time current correlation function by switching the time-dependent current to a time evolution propagator of the density matrices in a consistent way. In the present work, we will modify this traditional approach to suit the underlying quantum rate equations for properly accounting for the quantum coherence effects, i.e., the nondiagonal elements of density matrix, in calculation of quantum shot noise and develop a tractable computation technique in matrix form.; As applications, analytical and numerical investigations have been given in detail for three cases: (1) electron tunneling through a quantum dot connected to ferromagnetic leads with intradot spin-flip scattering, (2) spinless fermions tunneling through seriesly coupled quantum dots, and (3) side-coupled quantum dots, focusing on the shot noise as functions of bias-voltage and frequency. (Abstract shortened by UMI.)... |
