  A voltage pulse of a Lorentzian shape carrying a half of the flux quantum
excites out of a zero-temperature Fermi sea an electron in a mixed state, which
looks like a quasi-particle with an effectively fractional charge $e/2$. A
prominent feature of such an excitation is a narrow peak in the energy
distribution function laying exactly at the Fermi energy $ \mu$. Another
spectacular feature is that the distribution function has symmetric tails as
above as below $ \mu$, which results in a zero energy of an excitation. This
sounds improbable since at zero temperature all available states below $ \mu$
are fully occupied. The resolution is lying in the fact that such a voltage
pulse excites also electron-hole pairs which free some space below $ \mu$ and
thus allow a zero-energy quasi-particle to exist. I discuss also how to address
separately electron-hole pairs and a fractionally charged zero-energy
excitation in experiment.
