Quantum coherent versus classical coherent light

The paper shows that the Wigner distribution function of quantum optical co herent states, or of a superposition of such states, can be produced and me asured with a classical optical set-up using classical coherent light field s. This measurement cannot be done directly in quantum optics since the qua ntum phase space variables correspond to non-commuting operators. As an exa mple, the Wigner distribution function of Schrodinger cat states of light h as been measured. It is also shown that the possibility of measuring the Wi gner distribution function of quantum coherent states with classical cohere nt fields is unique in the sense that it cannot be extended to other quantu m states, not even to the incoherent limit of the superposition of coherent states.