  The state of a single particle injected onto the surface of the Fermi sea is
a pure state if the temperature is zero and is a mixed state if the temperature
is finite. Moreover, the state of an injected particle is orthogonal to the
state of the Fermi sea at zero temperature, while it is not orthogonal at
non-zero temperature. These changes in the quantum state of the injected
particles can be detected using the temperature dependence of the shot noise
that is generated when the particles one by one pass through a semitransparent
quantum point contact. Namely, the shot noise produced by the mixed state is
suppressed in comparison with the noise of the pure state. In addition, the
correlations between the injected particles and the underlying Fermi sea,
present at non-zero temperature, do enhance the shot noise. Furthermore,
antibunching of injected particles with possible thermal excitations coming
from another input channel of a quantum point contact does suppress shot noise.
Here I analyze in detail these three effects, which are responsible for the
temperature dependence of the shot noise, and discuss how to distinguish them
experimentally.
