Casting a quickened spell is a swift action. You can perform another action, even casting another spell, in the same round as you cast a quickened spell. A spell whose casting time is more than 1 round or 1 full-round action cannot be quickened. A quickened spell uses up a spell slot four levels higher than the spell's actual level. Casting a quickened spell doesn't provoke an attack of opportunity.

Quicken Spell

Metamagic

You can apply the effects of this feat to a spell cast spontaneously, so long as it has a casting time that is not more than 1 full-round action, without increasing the spell's casting time.