  Motivated by a recent experiment by L.-H. Reydellet et al., Phys. Rev. Lett.
90, 176803 (2003), we discuss an interpretation of photon-assisted shot noise
in mesoscopic multiprobe conductors in terms of electron-hole pair excitations.
AC-voltages are applied to the contacts of the sample. Of interest are
correlations resulting from the fact that electrons and holes are generated in
pairs. We show that with two out-of-phase ac-potentials of equal magnitude and
frequency, applied to different contacts, it is possible to trace out the
Hanbury Brown Twiss exchange interference correlations in a four probe
conductor. We calculate the distribution of Hanbury Brown Twiss phases for a
four-probe single channel chaotic dot.
