  An extra constant phase can be added to the wave function of a finite-length
portion of a chiral Fermi sea. This phase can be read-out with the help of an
imbalanced interferometer, where such a phase carrier interferes with the
reference Fermi sea. As a result of such interference, the same in value but
opposite in sign charge is appeared at interferometer's outputs. A phase
carrier consists of electron-hole pairs residing on the surface of the Fermi
sea. Importantly, these pairs are not only electrically neutral, but in
addition do not carry heat. A phase carrier can be created, for instance, with
the help of an on-demand single-electron source able to produce excitations
with a multiple-peak density profile.
