Measurement of the Wigner function of a cavity field via Autler-Townes spectroscopy

We show that the Wigner fuction of a cavity field can be constructed from t he spontaneous emission spectrum in driven three-level atomic systems. We c onsider two configurations, the upper- and lower-level couplings, in which the driving field is the quantized field inside a cavity. In the proposed m ethod, the Wiener function of the driving field is recovered in a straightf orward manner, without much mathematical manipulation of the experimental d ata, from the spontaneous emission spectra.