Antibunched photons emitted by a quantum point contact out of equilibrium.

Motivated by the experimental search for "GHz nonclassical light," we identify the conditions under which current fluctuations in a narrow constriction generate sub-Poissonian radiation. Antibunched electrons generically produce bunched photons, because the same photon mode can be populated by electrons decaying independently from a range of initial energies. Photon antibunching becomes possible at frequencies close to the applied voltage V�e/, when the initial energy range of a decaying electron is restricted. The condition for photon antibunching in a narrow frequency interval below eV/hbar reads SUM_n[Tn(1�Tn)]2