The quantum computational speed of a single Cooper Pair box
  The speed of computations is investigated by means of the orthogonality speed for a charged qubit interacting with a single cavity field prepared initially in a Fock state or Binomial state. We observe that the rate of the computational speed is related to the number of photons inside the cavity. Moreover, we show that the qubit-field coupling plays an opposite role, where the speed of computations is decreased as the coupling is increased. We suggest using the number of photons in the field as a control parameter to improve the speed of computations. 
A.-S.F.Obada, D.A.M.Abo-Kahla, N. Metwally and M. Abdel-Aty
quant-ph