  Waves fail to propagate in random media. First predicted for quantum
particles in the presence of a disordered potential, Anderson localization has
been observed also in classical acoustics, electromagnetism and optics. Here,
for the first time, we report the observation of Anderson localization of pairs
of entangled photons in a two-particle discrete quantum walk affected by
position dependent disorder. A quantum walk on a disordered lattice is realized
by an integrated array of interferometers fabricated in glass by femtosecond
laser writing. A novel technique is used to introduce a controlled phase shift
into each unit mesh of the network. Polarization entanglement is exploited to
simulate the different symmetries of the two-walker system. We are thus able to
experimentally investigate the genuine effect of (bosonic and fermionic)
statistics in the absence of interaction between the particles. We will show
how different types of randomness and the symmetry of the wave-function affect
the localization of the entangled walkers.
