Generation of phase states by two-photon absorption

A new method for producing a phase state by two-photon absorption is propos ed. We show that such a process conserves the phase of an initial coherent state \alpha] and converts it to \psi] = (\0]) + e(i phi)\1])/root 2, where alpha = \alpha\e(i phi). Therefore, we obtain desirable phase states by co ntrolling the phase of the initial coherent state. Appropriate materials wi th a reasonable two-photon absorption rate are proposed.