What are some potential applications of quantum teleportation?

[Strilanc]

Quantum teleportation let's you send quantum information over a classical communication channel by using previously-shared bell pairs (you can send 1 qubit by "consuming" 1 bell pair and sending 2 classical bits).

I was wondering what sorts of hypothetical applications this would have, similar to super dense coding letting you "store" bandwidth.

For example, if you had a very high latency quantum communication channel but a low latency classical channel then quantum teleportation let's you combine them to get a low latency quantum communication channel.

Or maybe you and a friend don't have a quantum channel between you, but there's a lab between you that can send bell pairs to each of you. Quantum teleportation let's you turn the lab-to-you+lab-to-friend one way channels into a you-to-friend two way channel (again assuming you have a classical channel). So, we can use QT to centralize bell pair production.

But these seem pretty tame to me. I'm also not sure what I would use a quantum channel for, besides cryptography.

Any ideas?

 

[haael]

With quantum teleportation you could have quantum computer clusters. You could have two quantum computers on the other sides of the world and with a teleport link they would behave as a single quantum computer with the sum of their qubits number.

 

[Strilanc]

With quantum teleportation you could have quantum computer clusters. You could have two quantum computers on the other sides of the world and with a teleport link they would behave as a single quantum computer with the sum of their qubits number.

That's a good application for quantum channels. It doesn't require quantum teleportation, though. (It can benefit from QT, e.g. the latency reduction if a quicker classical line is available, but works without it.)

*edit* Other applications for quantum channels, so indirectly benefiting from quantum teleportation: things like quantum money and quantum private queries.

I thought of another application. If you stored up a cache of bell pairs, and the quantum channel broke, you could start consuming the bell pairs and survive short outages without any service disruption.

 

[haael]

That's a good application for quantum channels. It doesn't require quantum teleportation, though. (It can benefit from QT, e.g. the latency reduction if a quicker classical line is available, but works without it.)

Are you sure? I don't think so.

According to my knowledge, quantum computers need to transfer quantum (non-collapsed) information between their qubits. Without that, you just have a series of individual 1-qubit computers. Joining quantum computers with a classical link would result only in linear performance boost.

With quantum teleportation however, you could join two N-qubit computers into one 2N-qubit computer, getting exponential performance boost as a result.

I might be wrong, but I think it is just like that. You need to transfer quantum (qubit) information between q-CPUs to do quantum computations. Classical bits exchange is not sufficient.

 

[Strilanc]

quantum computers need to transfer quantum (non-collapsed) information between their qubits. Without that, you just have a series of individual 1-qubit computers. Joining quantum computers with a classical link would result only in linear performance boost.

Quantum teleportation also requires you to send qubits in superposition without collapsing them (a bit more flexibly, but it still has to happen). It doesn't work if all you ever have is classical communication links. You need a pre-existing quantum channel to set it up over.

A quantum channel is anything that let's you transfer qubits in superposition without collapsing them. A piece of fiber optic cable is apparently reasonable at this task, for qubits encoded into the polarization of a photon. So you can allow quantum computers to communicate by sending qubits as photons over fiber to each other, without teleportation.

 

[haael]

OK, help me verify my knowledge.

There are 3 types of channels: classical, quantum and teleportation, right?

Classical channel transfers bits. I.e. zero and one.

Quantum channel transfers qubits. I.e. we may send an electron through it with yet unknown spin and check it on the other side. We can transfer full uncollapsed wavefunction using it.

Teleportation channel transfers bits, but operates on entangled particles on both sides, so if we disturb a particle on our side getting a bit from it and then wait for the bit from the channel, the resulting bits will be correlated. If we decide not to disturb our particle and use the bit from the channel instead to diagnose the particle, we will effectively have transferred a qubit.

That means, teleport link is effectively a quantum link operating over a classical link with help of pre-entangled particles. In other words, a load of pre-entangled particles allow as to upgrade a classical link into a quantum link.

Do I make any error here? I was always thinking that quantum channel and teleportation channel are the same.

Now you are asking what advantages does a teleport link have that a quantum link has not?

One application that comes to my mind is a holographic display. If you have a camera with enough load of entangled particles and a display, then you can make a movie with the camera and send the data. On the display we will have the information about photon phases that will allow us to recover the 3d image. I wonder if it's possible with the current technology.

Also, it should be possible to teleport quantum states over time (into the future) as opposed to teleporting over space. We could for example perform some experiment, collect the quantum data without watching, save the classical bits on a disk, put the quantum state in a fridge and go to sleep. Next day, we could use the bits to recover the data and perform some measurements. In other words, we could trigger some phenomenon, "freeze" its quantum state and watch it later, in different place and time.

 

[Strilanc]

OK, help me verify my knowledge.

There are 3 types of channels: classical, quantum and teleportation, right?

No, just 2 types. A teleportation channel is a quantum channel. All quantum channels preserve entanglement. If you have qubits X,Y,Z where X is entangled with Y and Z, and you send X over fiber, then now the other side has X and X should still be entangled with Y and Z.

 

[haael]

No, just 2 types. A teleportation channel is a quantum channel.

If so, then there are no applications for quantum teleportation more than for an ordinary optic fibre which is a quantum link already.

If we define a teleportation link as "classical channel plus entangled pairs in a fridge" then there might be some applications.

 

[Strilanc]

If so, then there are no applications for quantum teleportation more than for an ordinary optic fibre which is a quantum link already.

If we define a teleportation link as "classical channel plus entangled pairs in a fridge" then there might be some applications.

I would count saving up some quantum channel and storing it in a fridge as an application. Let's you keep communicating during temporary outages.