michael_nielsen

So, how could one discover quantum teleportation? Here's a very abbreviated piece of discovery fiction as a (not entirely serious) answer to that question!

The basic job for teleportation is for Alice to transmit an unknown quantum state a|0>+b|1> to Bob, without directly sending the quantum state or any quantum system.

Coming to this for the first time, you might hope that Alice would be able to measure her state, figure out the quantum amplitudes a and b, and send a classical description of those amplitudes to Bob, who could re-create the state.

Trouble is, it turns out to be impossible to do that in quantum mechanics. It's not just that it's difficult or hard to do, it's genuinely forbidden by the laws of physics!

In fact, in quantum mechanics it turns out that if you acquire information about a state through measurement, that actually damages the state. There's no way round this!

That seems discouraging. But maybe we can tip the problem upside down? Might it be possible for Alice to do a measurement that DOESN'T acquire any information about the amplitudes a and b, but somehow can still help Bob acquire the original state?

That sounds pretty unlikely. But if you know some classical cryptography, you'll know that something like this is done routinely in the cryptosystem known as a one-time pad. Here's how it works.