Generalized single qubit rotation gates in the presence of dephasing

Abstract

In this study we investigate the effect of dephasing on the performance of the gen- eralized quantum rotation gates implemented by adiabatic passage and static laser pulses proposed in (X.Lacour et al, 2006). The adiabatic passage technique used in the thesis is a stimulated Raman adiabatic passage (STIRAP) which is robust and efficient tool to transfer population between the two lower levels of a three lambda system keeping the population in the excited level negligible. Since the excited level is not populated, the spontaneous emission has no effect on the evolution of the three-level system. However, dephasing caused by collisions or phase fluctuations of the pumped fields influence the evolution and becomes a big challenge when implementing quantum gates. For this reason we study the performance of the quantum gates in the presence of dephasing. Lastly, by applying the quantum jump approach, we show that in an open system the dephasing introduces complex geometrical phases which cannot be recompensated as in the closed system. Numerical solutions for the complex geometrical phases are obtained assuming realistic dephasing rates.