  We study the photoelectric current generated by a driving light with
nonclassical photon statistics. Due to the nonclassical input photon
statistics, it is no longer enough to treat the driving light as a planar wave
as in classical physics. We make a quantum approach to study such problems, and
find that: when the driving light starts from a coherent state as the initial
state, our quantum treatment well returns the quasi-classical driving
description; when the the driving light is a generic state with a certain P
function, the full system dynamics can be reduced as the P function average of
many "branches" -- in each dynamics branch, the driving light starts from a
coherent state, thus again the system dynamics can be obtained in the above
quasi-classical way. Based on this quantum approach, it turns out the different
photon statistics does make differences to the photoelectric current. Among all
the classical light states with the same light intensity, we prove that the
input light with Poisson statistics generates the largest photoelectric
current, while a nonclassical sub-Poisson light could exceed this classical
upper bound.
