  We associate a half-integer number, called {\em the quantum index}, to
algebraic curves in the real plane satisfying to certain conditions. The area
encompassed by the logarithmic image of such curves is equal to $\pi^2$ times
the quantum index of the curve and thus has a discrete spectrum of values. We
use the quantum index to refine real enumerative geometry in a way consistent
with the Block-G\"ottsche invariants from tropical enumerative geometry.
