  The counterintuitive features of quantum physics challenge many common-sense
assumptions. In an interferometric quantum eraser experiment, one can actively
choose whether or not to erase which-path information, a particle feature, of
one quantum system and thus observe its wave feature via interference or not by
performing a suitable measurement on a distant quantum system entangled with
it. In all experiments performed to date, this choice took place either in the
past or, in some delayed-choice arrangements, in the future of the
interference. Thus in principle, physical communications between choice and
interference were not excluded. Here we report a quantum eraser experiment, in
which by enforcing Einstein locality no such communication is possible. This is
achieved by independent active choices, which are space-like separated from the
interference. Our setup employs hybrid path-polarization entangled photon pairs
which are distributed over an optical fiber link of 55 m in one experiment, or
over a free-space link of 144 km in another. No naive realistic picture is
compatible with our results because whether a quantum could be seen as showing
particle- or wave-like behavior would depend on a causally disconnected choice.
It is therefore suggestive to abandon such pictures altogether.
