Perturbative formulation and nonadiabatic corrections in adiabatic quantum-computing schemes

Adiabatic limit is the presumption of the adiabatic geometric quantum computation and of the adiabatic quantum algorithm. But in reality, the variation speed of the Hamiltonian is finite. Here we develop a general formulation of adiabatic quantum computing, which accurately describes the evolution of the quantum state in a perturbative way, in which the adiabatic limit is the zeroth-order approximation. As an application of this formulation, nonadiabatic correction or error is estimated for several physical implementations of the adiabatic geometric gates. A quantum-computing process consisting of many adiabatic gate operations is considered, for which the total nonadiabatic error is found to be about the sum of those of all the gates. This is a useful constraint on the computational power. The formalism is also briefly applied to the adiabatic quantum algorithm.