- #1
Dragonfall
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The other thread was going too off-topic, so I'll repost here. Why is this not possible, without considering FTL signals?
I'm just going over what I'm asking again since I wasn't clear before:
Bob takes n+1 qubits, all initiated at |0> (the first n being input registers and the last is an output register), and sends the first n through an n-fold Hadamard gate. This results in the superposition
[tex]\mid\Psi\rangle =\frac{1}{\sqrt{2^n}}\sum_{i=0}^{2^n-1}\mid i\rangle\mid 0\rangle[/tex]
Bob then chooses some function f bounded above by 2^n-1, then finds a unitary operator which implements the function:
[tex]U_f\mid x\rangle\mid 0\rangle =\mid x\rangle\mid f(x)\rangle[/tex]
Bob then sends [itex]U_f\mid\Psi\rangle[/itex] to Alice. Alice now has n+1 qubits with loads of information about the function f. Alice would like to learn a PARTICULAR VALUE of f (not a random one). Can she do it?