According to [IBM's website](https://www.ibm.com/developerworks/linux/library/l-quant/),

> _[...]where we would [classically] have done an assignment (x=y), we instead initialize the target (x=0) and use exclusive or (x^=y)._

This sounds like x is a copy (clone) of y, however [cloning is impossible in quantum mechanics](http://en.wikipedia.org/wiki/No-cloning_theorem). What's going on?