In single-particle or intraparticle entanglement, two degrees of freedom of a
single particle, e.g., momentum and polarization of a single photon, are
entangled. Single-particle entanglement (SPE) provides a source of non
classical correlations which can be exploited both in quantum communication
protocols and in experimental tests of noncontextuality based on the
Kochen-Specker theorem. Furthermore, SPE is robust under decoherence phenomena.
Here, we show that single-particle entangled states of single photons can be
produced from attenuated sources of light, even classical ones. To
experimentally certify the entanglement, we perform a Bell test, observing a
violation of the Clauser, Horne, Shimony and Holt (CHSH) inequality. On the one
hand, we show that this entanglement can be achieved even in a classical light
beam, provided that first-order coherence is maintained between the degrees of
freedom involved in the entanglement. On the other hand, we prove that filtered
and attenuated light sources provide a flux of independent SPE photons that,
from a statistical point of view, are indistinguishable from those generated by
a single photon source. This has important consequences, since it demonstrates
that cheap, compact, and low power entangled photon sources can be used for a
range of quantum technology applications