The kinetics of electron transport in quantum point contacts has been
studied by means of low-frequency noise spectroscopy. The temperature
and frequency (Lorentzian or 1/f) dependences of the noise intensity a
re found to be device specific, in contrast to the conductance depende
nce, which universally exhibits a strong quantum size effect at low te
mperatures. The origin of the Lorentzian noise spectrum is electron tr
apping and release at a single trap close to the point contact, and is
connected to random resistance switching in the time domain. The 1/f
noise in other point contacts is attributed to a collection of traps i
n the vicinity of the point contact. A comprehensive model is presente
d which accounts for the conductance and temperature dependences of th
e noise in quantum point contacts.