Internal consistency of the method of two-time thermal Green's functions

Yu. A. Tserkovnikov

Yu. A. Tserkovnikov

Wei Li, Hongmin Zhao, Jia-tih Lin

Using two-time Green's function we analyze the effect of temperature on the Mølmer and Sørensen (M–S) model of cold trapped ion quantum computer. A formula for the deviation of an internal state from its ground state is derived in the first-order approximation. The fluctuation of internal state caused by thermal motion is also discussed. The deviation of internal state when different trap parameters changes with the temperature are given too. The upper temperature limit for regular quantum computation is obtained and our result is in agreement with experiment.

Vladimir D. Ozrin

Andro Sabashvili

This work describes a new formalism for Fermionic thermal Greens functions that are discretized in imaginary time. The discretization makes the thermal Greens function periodic in imaginary (Matsubara) frequency space and requires a generalisation of the Dyson equation and Luttinger-Ward-Baym-Kadanoff functional. A Pade method is used to perform an analytic continuation of the periodized Matsubara Greens function to real frequencies which conserves the spectral weight and thus the discontinuity of the corresponding real time Greens function at t = 0. Due to the Matsubara Greens function periodicity, the discrete imaginary frequency space is relatively small which allows calculations at the extremely high precision which is necessary to perform a reliable Pade fit. We use the method to compute the single particle spectral function and energy loss function for doped bilayer graphene in the two-band limit, described by parabolic dispersion and Coulomb interaction. Calculations are performed in both the random phase approximation (RPA) and the fully self-consistent GW approximation. The formalism is also applied to dynamical mean field the- ory calculations using iterated perturbation theory (IPT) for the paramagnetic Hubbard model.

В. Л. Бонч-Бруевич