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.
"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