> I'm no physicist, but doesn't Heisenberg's Uncertainty Principle forbid
> making exact quantum-level measurements, hence exact copies? If so, then
> all this talk of making exact copies is fantasy.
> Norman Samish
You can't *specifically* copy a quantum state, but you can create
systems in *every possible* quantum state (of a finite size), hence you
can make an ensemble which contains a copy of a given quantum system.
You can't say which specific item in the ensemble is the copy, but you
can make a copy. That may or may not be sufficient for a particular
thought experiment to go forward.
In practice most people believe that consciousness does not depend
critically on quantum states, so making a copy of a person's mind would
not be affected by these considerations.