  The discovery of artificial gauge fields, controlling the dynamics of
uncharged particles that otherwise elude the influence of standard electric or
magnetic fields, has revolutionized the field of quantum simulation. Hence,
developing new techniques to induce those fields is essential to boost quantum
simulation in photonic structures. Here, we experimentally demonstrate in a
photonic lattice the generation of an artificial gauge field by modifying the
input state, overcoming the need to modify the geometry along the evolution or
imposing the presence of external fields. In particular, we show that an
effective magnetic flux naturally appears when light beams carrying orbital
angular momentum are injected into waveguide lattices with certain
configurations. To demonstrate the existence of that flux, we measure the
resulting Aharonov-Bohm caging effect. Therefore, we prove the possibility of
switching on and off artificial gauge fields by changing the topological charge
of the input state, paving the way to access different topological regimes in
one single structure, which represents an important step forward for optical
quantum simulation.
