# B Is this equal to teleporting information?

1. Oct 21, 2016

### TJung

2. Oct 21, 2016

### secur

Yes, quantum "teleportation" does transmit information. The speed of transmission is <= c (light speed), so doesn't violate relativity - of course.

3. Oct 21, 2016

### Strilanc

Quantum teleportation is a thing, but it's probably not what you're picturing in your head. It's more like...

Alice and Bob share an entangled EPR pair $S$; qubits in a special state where they agree along the Z axis and also they agree along the X axis.
Alice wants to send a qubit $M$ to Bob.
Alice compares $M$ to $S_A$ along the X axis, getting a SAME_X or OPPOSITE_X result.
Alice also compares $M$ to $S_A$ along the Z axis, getting a SAME_Z or OPPOSITE_Z result.
Alice's results tell her how Bob's $S_B$ relate to $M$.
For any OPPOSITE results, Alice tells Bob he needs to flip over $S_B$ to fix the problem.
Then she tells him he's good to go, $S_B$ is now SAME as $M$ was along both the X and Z axes.
$M$ has been moved into $S_B$.

It's exactly analogous to a classical one-time pad. Instead of sending the information directly, you say how the information relates to a shared secret.

4. Oct 21, 2016

### rootone

Yes, you just did that by asking the question on the internet.

5. Oct 21, 2016

### TJung

I mean, is there FTL information transfer?

6. Oct 22, 2016

### Carrock

7. Oct 22, 2016

### TJung

So what exactly is being teleported? I understand teleportation as the instantaneous transfer of something, so FTL.

8. Oct 22, 2016

### maxverywell

No you cannot teleport (FTL) information or energy or matter.
In quantum teleportation schemes they "teleport" a quantum state $\psi$, but a classical channel of communication is always needed in order to complete the teleportation (so the information is not sent FTL, but at the speed of light). Otherwise, the receiver can only hope that he will get the state $\psi$ on his system and not some other state. With the classically sent additional information, the probability that the receiver will get $\psi$ can become 1.

Last edited: Oct 22, 2016
9. Oct 23, 2016

### TJung

So when they talk about quantum internet, its about security, not speed?

10. Oct 23, 2016

### Staff: Mentor

Yes. Google for "quantum key distribution".

11. Oct 23, 2016

### Strilanc

It's also about flexibility and historically-surprising facts.