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Comment by TheRealPomax | Hacker News Reader

It's only called teleportation, it has nothing to do with teleporting matter in the sci-fi sense.

Quantum teleportation is about preparing two particles so that that by destroying the original particle's state by measuring it, and then transmitting a specific bit pattern as regular information, constrained by the speed of light, the other particle can be made to have the identical quantum state as was measured on the now destroyed particle.

The quantum state is (destructively) "teleported" from one particle onto another (preallocated) particle, obeying the rather mundane rules of classical physics.

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In theory, could that be used on a block of random matter and a, say, banana, so that you can get lightspeed transmission of banana-ness?

Realistic theory? No, not even remotely.

The problem comes from having to measure the quantum state of every quantum particle in that banana and transmitting the bits necessary to perform the state transfer. We're talking destructively reading out well over 10^25 particles, turning that into tens of yottabytes of data, and then transmitting that data with error correction over distances that you can't just... you know... ship a banana over.

And then you'd have to receive that data in a way that either lets you perform the transfer in real time, or in a way that lets you store that data so you can transfer the quantum states one by one or in small batches.

And that's if you're okay with "Scanning" the original banana in a way that destroys the banana as yous scan it. Not the quantum states, the actual banana: the destructive read of particles will cause nuclear reactions and so very quickly you're no longer scanning "a banana" but "messed up subatomic partilces".

I don’t like the term “observer” because it implies it’s an entirely passive thing.

Why is it that we cannot passively observe quantum states? Why does observation necessarily have to be destructive?

There is no such thing as "passive" observation: something has to change in order for information to become known. Without a transfer of energy, no observation can be made, so either we absorb the particle to register that energy (and then it is literally gone after measurement) or we stimulate the particle into emission (drastically changing its quantum state), or we "poke" the particle by throwing things at it (changing its quantum state in the process).

To “observe” something, you need to interact with it in some way, such as bouncing a photon off it. That interaction changes the quantum state.

How is that different or better than just transmitting information at light speed over fiber? Excuse the ignorant question.

It is (in theory) capable of transmitting the entire quantum state.

It's the star trek transporter version of teleportation for quantum mechanical systems.

  It's the star trek 
  transporter version of 
  teleportation for quantum 
  mechanical systems.

No. No it isn't. It's not teleportation, because transit still occurs at non-instantaneous rates, and it is effectively slower than light speed travel when you include the overhead of the protocol.

A near-light-speed rocket ship could literally accomplish the same thing.

It is not a gateway technology that opens a portal to a destination. It clones state, and can replicate an infinite series of clones at a station, via transmission of state.

At best it could be called a matter replicator, but it is not teleportation.

Oh, I see - the transmitted information is far "less" than the quantum state itself.

indeed. To convey the single quantum state |φ> we only need to send 2 bits, provided we pre-allocated our "receiving" particle correctly (which as far as we currently know has to be one of an entangled pair).

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