  We use Raman-assisted tunneling in an optical superlattice to generate large
tunable effective magnetic fields for ultracold atoms. When hopping in the
lattice, the accumulated phase shift by an atom is equivalent to the
Aharonov-Bohm phase of a charged particle exposed to a staggered magnetic field
of large magnitude, on the order of one flux quantum per plaquette. We study
the ground state of this system and observe that the frustration induced by the
magnetic field can lead to a degenerate ground state for non-interacting
particles. We provide a measurement of the local phase acquired from
Raman-induced tunneling, demonstrating time-reversal symmetry breaking of the
underlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single
atoms in the lattice exposed to the magnetic field is directly revealed.
