I suppose there is a type of encryption that is not crackable using quantum computers: a one-time pad such as the Vigenère cipher. This is a cipher with a keypad that has at least the length of the encoded string and will be used only once. This cipher is impossible to crack even with a quantum computer.
I will explain why:
Let's assume our plain textplaintext is
ABCD. The corresponding key could be
1234. If you encode it then you get
XYZW. Now you can use
1234 to get
4678 to get
EFGH what might be a valid sentence too.
So the problem is that nobody can decide whether you meant
EFGH without knowing your key.
The only reason this kind of encryption can be cracked is that the users are lazy and use a key twice. And then you can try to crack it. Other problems are, as @peterh stated that one-time-pads require a secret channel to be shared