Quantum bits and superposition displaced Fock states of the cavity field
  We study the effects of counter rotating terms in the interaction of quantized light with a two-level atom, by using the method of small rotations. We give an expression for the wave function of the composed system atom plus field and point out one initial wave function that generates a quantum bit of the electromagnetic field with arbitrary amplitudes. 
L. Arevalo Aguilar and H. Moya-Cessa