  Motivated by recent progress in electron quantum optics, we revisit the
question of single-electron entanglement, specifically whether the state of a
single electron in a superposition of two separate spatial modes should be
considered entangled. We first discuss a gedanken experiment with
single-electron sources and detectors, and demonstrate deterministic (i. e.
without post-selection) Bell inequality violation. This implies that the
single-electron state is indeed entangled and, furthermore, nonlocal. We then
present an experimental scheme where single-electron entanglement can be
observed via measurements of the average currents and zero-frequency current
cross-correlators in an electronic Hanbury Brown-Twiss interferometer driven by
Lorentzian voltage pulses. We show that single-electron entanglement is
detectable under realistic operating conditions. Our work settles the question
of single-electron entanglement and opens promising perspectives for future
experiments.
