Although the unit of charge in nature is a
fundamental constant, the charge of individual quasiparticles in some
low-dimensional systems may be fractionalized. Quantum One-Dimensional (1D)
systems, for instance, are theoretically predicted to carry charge in units
smaller than the electron charge e. Unlike 2D systems, the charge of
these excitations is not quantized and depends directly on the strength of the
Coulomb interactions. For example, in a 1D system with momentum
conservation, it is predicted that the charge of a unidirectional electron that
is injected into the wire decomposes into right and left moving charge
excitations carrying fractional charges f0e and (1-f0)e
respectively. f0 approaches
unity for non-interacting electrons and is less than one for repulsive
interactions. In this work we provide the first experimental evidence for charge
fractionalization in 1D. Unidirectional electrons are injected at the bulk of a
wire and the imbalance in the currents detected at two drains on opposite sides
of the injection region is used to determine f0. Our results elucidate further the
collective nature of electrons in 1D.