Yes, with a quantum computer you could hypothetically halve the effectiveness of AES (so AES-256 would be roughly equivalent to AES-128). This would make a 128-bit key fairly weak (and AES-128 is fairly common still)… a 64-bit space can be brute forced on regular computers in a reasonable amount of time. This doesn’t mean it will be cheap or feasible to break 128-bit AES on quantum computers, though. Maybe it can do it in roughly 2^64 computations, but if each operation is slow it still might not be feasible. At least initially it would probably be expensive to crack so hopefully they’d only bother for really targeted stuff.
Yes, with a quantum computer you could hypothetically halve the effectiveness of AES (so AES-256 would be roughly equivalent to AES-128). This would make a 128-bit key fairly weak (and AES-128 is fairly common still)… a 64-bit space can be brute forced on regular computers in a reasonable amount of time. This doesn’t mean it will be cheap or feasible to break 128-bit AES on quantum computers, though. Maybe it can do it in roughly 2^64 computations, but if each operation is slow it still might not be feasible. At least initially it would probably be expensive to crack so hopefully they’d only bother for really targeted stuff.