How can free will exist if God is omnipotent?
First of all, I assume you are asking about free will in light of God’s sovereignty, not his omnipotence. I see no logical problem in God being all-powerful preventing him from using his power to create a sentient being with free will. I know of no scholar, theologian or skeptic of Christianity who has raised this issue, so I consider the problem solved.
The potential logical problem is not with God being so powerful he could not create a being with free will. The problem is with God being sovereign, one of his assumed traits, that creates a problem. The doctrine of God’s sovereignty proposes that God’s will is always done. If God decrees something, then if he is sovereign, what he decrees will be done. However, if we have free will, then some will argue that this means that things happen which oppose God’s will–and thus the possible contradiction. This apparent contradiction is why some have proposed that humans do not have real free will before baptism. This is the theology of Augustine, Luther, Zwingli and Calvin. The doctrine which proposes that God chooses who will be saved and who will be lost (and associated ideas I will not go into here) is sometimes called Calvinism. The doctrine is sometimes called double predestination. In other words, because God is sovereign, he determines both who will be saved and who will be lost. If so, then our free will is very limited, and God predestines both the good and the evil that we do.
I definitely do NOT agree with this doctrine. Not at all! Instead I believe that the way around this apparent “contradiction” is this. God is sovereign, but it is his sovereign will that we, his highest creation, created in his image, have sovereign free will of our own. In other words, it is God’s sovereign will that we human beings (and angels as well?) have free will. The way Thomas Aquinas put it:
“God, therefore, is the first cause, who moves causes both natural and voluntary. And just as by moving natural causes He does not prevent their actions from being natural, so by moving voluntary causes He does not deprive their actions of being voluntary; but rather is He the cause of this very thing in them, for He operates in each thing according to his own nature.”
If Aquinas is right (and I believe he is), then God used his sovereignty to give us our own limited “local” sovereignty, and this is part of our God-image. In Matthew 6:10 Jesus gives us a model prayer which includes the prayer that “your will be done.” Apparently, on some level, God’s “will” is not always done. It is not God’s will that genocide occurs or that you pick a particular marriage partner or even when a particular light turns from red to green. One of God’s greatest gifts which is the result, not of weakness, but of his power, is that out of love he gave us free will.
I went on a bit of a tangent here. If you want me to return to the actual question about God’s power and our free will, I will do so, but in that case you will need to explain your question more thoroughly, as I do not see an obvious problem there.