  One-dimensional metals, such as quantum wires or carbon nanotubes, can carry
charge in arbitrary units, smaller or larger than a single electron charge.
However, according to Luttinger theory, which describes the low-energy
excitations of such systems, when a single electron is injected by tunneling
into the middle of such a wire, it will tend to break up into separate charge
pulses, moving in opposite directions, which carry definite fractions $f$ and
$(1-f)$ of the electron charge, determined by a parameter $g$ that measures the
strength of charge interactions in the wire. (The injected electron will also
produce a spin excitation, which will travel at a different velocity than the
charge excitations.) Observing charge fractionalization physics in an
experiment is a challenge in those (nonchiral) low-dimensional systems which
are adiabatically coupled to Fermi liquid leads. We theoretically discuss a
first important step towards the observation of charge fractionalization in
quantum wires based on momentum-resolved tunneling and multi-terminal
geometries, and explain the recent experimental results of H. Steinberg {\it et
al.}, Nature Physics {\bf 4}, 116 (2008).
