Quantum interferences, where two electronic pathways “compete” in a manner akin to the interference of separate propagating waves, are often exploited in atomic systems to realize a variety of exotic phenomena, such as electromagnetically induced transparency, slow light and lasing without inversion. In crystalline materials, quantum interferences can sometimes be difficult to discern with conventional probes, even if their consequences may be just as profound. In this talk, I will discuss how optical second harmonic generation spectroscopy reveals a hidden quantum interference in the LnAlSi (Ln = lanthanide) family of Weyl semimetals, a class of topologically ordered matter defined by massless, chiral quasiparticles, and I will discuss how this previously concealed feature of their shared band structure plays a role in their electronic and optical properties.