For symmetric encryption quantum computing doesn't do much. It reduces the running time of brute-force search by sqrt. So in 2^128 operations you could brute force a 2^256 big search space (i.e. a 256 bit key).
That's why many symmetric systems have moved to a 256 bit key. It makes them quantum safe because 2^128 operations are considered impossible. (According to some physicsists it is guaranteed to boil the oceans).
