  Quantum plasma with arbitrary degree degeneration of electronic gas is
considered. Plasma is in two external electromagnetic fields. It is required to
find the plasma response on this fields. From Wigner kinetic equation for the
quantum collisionless plasmas distribution function in square-law approach on
sizes of vector potentials of two electric fields is received. The formula for
calculation electric current at any temperature (any degree of degeneration of
electronic gas) is deduced. This formula contains an one-dimensional
quadrature. It is shown, that the nonlinearity account leads to occurrence the
longitudinal electric current directed along a wave vectors. This longitudinal
current is orthogonal to a known transversal current, received at the linear
analysis. The case of small values of wave numbers is considered. It is shown,
that in case of small values of wave numbers a longitudinal current in quantum
plasma coincides with a longitudinal current in classical plasma.
