A dynamics of a nuclear-spin quantum computer with a large number of qubits is considered using a perturbation approach. Small parameters are introduced and used to compute the error in an implementation of an entanglement between remote qubits, using a sequence of radio-frequency pulses. The error is computed up to the different orders of the perturbation theory and tested using exact numerical solution.
G. P. Berman. D. I. Kamenev. V. I. Tsifrinovich. "Perturbation approach for nuclear magnetic resonance solid-state quantum computation." J. Appl. Math. 2003 (1) 35 - 53, 23 January 2003. https://doi.org/10.1155/S1110757X03110182