A quantum shift, or quantum leap, in common parlance borrows the discontinuity in energy levels in quantum physics as an analogy for a sudden change (compared to the continuous changes in classical descriptions of physical characteristics).
The size is not always part of the analogy except in that the "quantum shift" is far larger in all circumstances than the infinitesimal changes in classical systems. Relative to an infinitesimal the quantum is huge [analytically it is infinitely larger, but the metaphoric analogy doesn't stretch that far].
A quantum shift, or quantum leap, in common parlance borrows the discontinuity in energy levels in quantum physics as an analogy for a sudden change (compared to the continuous changes in classical descriptions of physical characteristics).
The size is not always part of the analogy except in that the "quantum shift" is far larger in all circumstances than the infinitesimal changes in classical systems. Relative to an infinitesimal the quantum is huge [analytically it is infinitely larger, but the metaphoric analogy doesn't stretch that far].
FWIW.