  We propose a realizable experimental scheme to prepare a superposition of the
vacuum and one-photon states using a typical cavity QED-setup. This is
different from previous schemes, where the superposition state of the field is
generated by resonant atom-field interaction and the cavity is initially empty.
Here, we consider only dispersive atom-field interaction and the initial state
of the cavity field is coherent. Then, we determine the parameters to prepare
the desired state via atomic postselection. We also include the effect of
cavity losses and detection imperfections in our analysis, against which this
preparation of the optical qubit in a real Fabry-P\'{e}rot superconducting
cavity is robust. Additionally, we show that this scheme can be used for the
preparation of other photon number Fock state superpositions. In summary, our
task is achieved with a high fidelity and a postselection probability within
experimental reach
