Experimental realization of an electromagnetically induced binary photonic lattice with tunable flat band

We experimentally and theoretically demonstrate an electromagnetically induced binary photonic lattice with an instantaneously tunable flat band in a three-level ⁸⁵Rb atomic configuration. The transmitted binary patterns result from the diffraction of an injected Gaussian probe beam through the atomic vapor cell, in which the refractive index is modulated by a binary coupling field with alternating high- and low-intensity peaks under electromagnetically induced transparency. The binary coupling field is established by spatially superimposing two standing-wave fields whose periods differ by a factor of two. The transmitted patterns and the flat band can be readily modulated via controllable atomic coherence. Crucially, by tuning the Rabi frequencies to engineer the refractive index contrast, instantaneous switching of the flat band is achieved. This investigation provides a new method for producing tunable binary photonic lattices, which can serve as a promising platform for investigating the dynamical evolutions of wave packets.