  Glass, a ubiquitous state of matter like a frozen liquid, is a seminal issue
across fundamental and applied sciences and has long been investigated in the
framework of classical mechanics. A challenge in glass physics is the
exploration of the quantum-mechanical behaviour of glass. Experimentally,
however, the real quantum manifestation of glass and the relationship between
classical and quantum glass are totally unknown and remain to be observed in
real systems. Here, we report the direct observation of classical-to-quantum
evolution in the frustration-induced charge glass state exhibited by
interacting electrons in organic materials. We employ Raman spectroscopy to
capture a snapshot of the charge density distribution of each molecule in a
series of charge glasses formed on triangular lattices with different
geometrical frustrations. In less frustrated glass, the charge density profile
exhibits a particle-like two-valued distribution; however, it becomes
continuous and narrowed with increasing frustration, demonstrating the
classical-to-quantum crossover. Moreover, the charge density distribution shows
contrasting temperature evolution in classical and quantum glasses, enabling us
to delineate energy landscapes with distinct features. The present result is
the first to experimentally identify the quantum charge glass and show how it
emerges from classical glass.
