  Emission of pairs of photons in the interface metal-dielectric under the
laser excitation arising due to the time-dependent perturbation of the
zero-point fluctuations of the electromagnetic field by photons of the laser is
considered. The enhancement of this emission by surface plasmons may be used
for getting polarization-entangled photons. A possibility to compensate the
energy of the zero-point fluctuations of bosons by other fluctuations with
negative energy is discussed.

Optics