Decoherence of the quantum logic gate implemented with the Jaynes-Cummings model
Hiroo Azuma
Abstract
In this paper, we investigate decoherence of Knill, Laflamme, and Milburn's nonlinear sign-shift gate that is implemented with the Jaynes-Cummings model. We analyze it by two methods. In the first method, we introduce a stochastic variable as an external magnetic field, and we let it couple with a magnetic dipole moment of a two-level atom. We examine this model using a semiclassical theory. The results of the Monte Carlo simulations under the semiclassical approximation correspond well with those obtained with the quantum mechanical perturbation theory for the stochastic process. In the second method, we study a master equation of the Jaynes-Cummings model with cavity losses in a fully quantum mechanical manner. We solve the master equation numerically with the Runge-Kutta method. For both semiclassical and fully quantum mechanical analyses, we can observe both the $\mbox{T}_{1}$ and $\mbox{T}_{2}$ decays. This paper is a sequel of the reference [H.~Azuma, Prog. Theor. Phys. {\bf 126}, 369 (2011)].