I can't help but imagine that somehow there's an abuse for this...
As for the idea-VERY powerful spell. The CC is weak, but the denial effect is huge. It's an interesting idea, but very worrisome.
Also to note: Sanctuary will block the denial, but still...
Let me put this for you :
Case 1 :
Consider killing a dragon of 5 HP.
2
for shockwave / Eagle Eye to reduce HP to 1 / 2
4
for quanta vortex to kill the dragon
total quanta usage : 6 quanta to destroy 10 quanta of opponent.
Opponent loses 10 quanta and a dragon (one card)
You lose 6 quanta and 2 spell cards.
Net result : you lose 1 card in exchange for destroying 4 net quanta of opponent and prevent further damage caused by the dragon.
Case 2 :
You use a single lightning on opponent's dragon of 5 HP
New result : You lose 2
to prevent further damage caused by the dragon.
That doesn't seem too unbalanced for me, at least in the case of a 10|5 dragon.