A scheme is proposed for the reconstruction of two-mode entangled states in
cavity QED and ion traps. For a two-mode field we show that the Wigner
function can be obtained by measuring the probability of a two-level atom
being in ground states after resonant interaction with two classical fields
and dispersive interaction with the two-mode cavity field displaced by
resonant sources. For the two-dimensional motion of a trapped ion the Wigner
function is obtained by measuring the probability of the ion in its ground
electronic state after displacing the ion motion and then resonantly exciting
the ion.