  The mobility edge (ME) is a crucial concept in understanding localization
physics, marking the critical transition between extended and localized states
in the energy spectrum. Anderson localization scaling theory predicts the
absence of ME in lower dimensional systems. Hence, the search for exact MEs,
particularly for single particles in lower dimensions, has recently garnered
significant interest in both theoretical and experimental studies, resulting in
notable progress. However, several open questions remain, including the
possibility of a single system exhibiting multiple MEs and the continual
existence of extended states, even within the strong disorder domain. Here, we
provide experimental evidence to address these questions by utilizing a
quasiperiodic mosaic lattice with meticulously designed nanophotonic circuits.
Our observations demonstrate the coexistence of extended and localized states
in lattices with broken duality symmetry and varying modulation periods. By
single site injection and scanning the disorder level, we could approximately
probe the ME of the modulated lattice. These results corroborate recent
theoretical predictions, introduce a new avenue for investigating ME physics,
and offer inspiration for further exploration of ME physics in the quantum
regime using hybrid integrated photonic devices.
