  The model of interacting fermion systems in one dimension known as
Tomonaga-Luttinger liquid (TLL) provides a simple and exactly solvable
theoretical framework, predicting various intriguing physical properties.
Evidence of TLL has been observed as power-law behavior in the electronic
transport and momentum-resolved spectroscopy on various types of
one-dimensional (1D) conductors. However, these measurements, which rely on dc
transport involving tunneling processes, cannot identify the eigenmodes of the
TLL, i.e., collective excitations characterized by non-trivial effective charge
e* and charge velocity v*. The elementary process of charge fractionalization,
a phenomenon predicted to occur at the junction of a TLL and non-interacting
leads, has not been observed. Here we report time-resolved transport
measurements on an artificial TLL comprised of coupled integer quantum Hall
edge channels, successfully identifying single charge fractionalization
processes. An electron wave packet with charge e incident from a
non-interacting region breaks up into several fractionalized charge wave
packets at the edges of the artificial TLL region, from which e* and v* can be
directly evaluated. These results are informative for elucidating the nature of
TLLs and low-energy excitations in the edge channels.
