I wonder how a quantum internet would be different than the binary one.
If these bits are blocked, no teleportation happens.
2. Displacement distance & velocity?
3. Energy consumed?
4. Is it really a teleportation?
2. Short & speed of light.
3. Irrelevant, since this is about whether it was actually doable, not about doing it efficiently.
4. The output particle is impossible to distinguish from the input one, but it didn't travel from input to output, so... how else would you define "real" teleportation?
how else would you define
Put a red marble and a blue marble in a sock, and then close your eyes and withdraw one marble from the sock. Place it in a mitten, and send the mitten to a friend.
Then we claim that the person who looks at their marble first has defined the reality of the other by default, and that qualifies as teleportation?
Teleportation has been demonstrated as a thought experiment countless times, and this doesn't pass the smell test. The concept of teleportation is instantaneous transportation of physical objects with mass and volume across arbitrarily large distances, seemingly as if stopping time and stepping through a door that connected point A and point B, in order to skip over the effort of transiting real physical distance.
This concept may be unrealistic, but we don't squat on antiquated terms like luminiferous ether when we conceptualize quantum foam.
There's this academic inertia to opportunistically squat on a word with a loaded meaning, all to gain favor and generate buzz and hype.
People desperately want recognition for a contrivance by leaning on a word. They know that using the word "teleportation" to describe something less exciting will provoke magical thinking among outsiders.
Since this process cannot produce effects faster than light, it's not even a slight improvement beyond radio or lasers or any form of radiant communication.
People don't refer to these efforts appropriately. The objective of these experiments is tamper evidence for quantum communication channels, and nothing more.
So, no particles were moved, it's just cloning the state of one particle to another. It's also important, but it's not something like the "beam me up" type of teleportation.
I'm not even sure if the ansible interface is actually described anywhere in that book....
This is "teleportation" in the same sense that Chinese skateboards with electric motors and debatably-safe lithium batteries duct-taped to them are "hoverboards."
A brief review of how quantum teleportation works. (I have a diagram in quirk that might help with the explanation
You start off with two qubits in a known state, say |0>. You then shift one of the qubits (using a Hadamard gate) into a equally mixed state of
qubit_1 = k(|0>+|1>)
and then use a controlled NOT gate to put the entire system in the state of
qubit_2 = k(|00>+|11>)
(where k = 1/sqrt(2)).
So you then ship one of the qubits off to your friend in Antarctica (say, qubit_1). You then pull out qubit_3. Now, let's say it's also in some known state |0> to begin with, and then you apply a bunch of gate operations to it, resulting in it being in the following state:
qubit_3 = a|0> + b|1>
Where a and b are two complex numbers whose magnitude sums to one.
You use another controlled not gate, this time, qubit_3 will act on qubit_2. This now has entangled qubit_3 into the qubit_1 and qubit_2 system. Finally, you apply another Hadamard gate to qubit_3. The system is now in the following state
|Psi> = |00>(a|0>+b|1>) + |01>(a|1>+b|0>)
+|10>(a|0>-b|1>) + |11>(a|1>-b|0>)
Now, you measure the two qubits that you control. Doing this causes the full state to collapse to one of the four above states. If you measure |11> then your friends particle is in the following state:
|Psi'> = a|1>-b|0>
The important thing to note here, is that from your perspective, the collapse happens immediately. The submitting of the classical information is just to 'patch up' the quantum state that got slightly out of whack.
Now, suppose your friend has the ability to clone qubits. You and your friend agree ahead of time when you'll perform the measurement.
Once the measurement is performed, your friend makes a large number of clones of the resulting state. He can then extract statistically the values of a and b (values of which, you had control over).
So not only would we be able to do FTL communication, we'd basically also have bandwidth limited only by the number of copies your friend could make.
I was about ask: Why is cloning a problem, but not a downconverter crystal (specifically a Type-0 SPDC ) that creates two photons with the same polarization as the input?
Then I realized: the two output photons are also entangled so you can only make 1 independent measurement of the pair.
By the way; the math reason for the impossibility of cloning states boils down to the fact that Quantum State evolution is described by a unitary operator. The linear algebra shows that this means that you can't have a process that takes a state
Q(|psi> x |r>) => |psi> x |psi>
That said; I find it very surprising that causality gets preserved in regular quantum mechanics by a completely unexpected mechanism, namely unitary state evolution. Regular QM doesn't know about special relativity, or its needs, and by pure accident it seems to prevent a giant loophole that would play havoc with causality.
Also, think about the way teleportation in computer games works.
Critical point: for each particle you want to "teleport", you have recipient particle standing by to receive it.
I'm not certain whether somehow mass-entangling an entire object with something else that receives its state and becomes a perfect (or near perfect because real life doesn't have "Heisenberg compensators" like Trek, to compensate for the Heisenberging) copy of the original is more or less ridiculous than Star Trek's version.
Is it ever explicitly called out that teleportation instantaneously moves matter?
I'm not a huge fan, but from what I've seen there is a max range they can teleport. Even taking them orbiting a planet, it usually take about 2-3 seconds or so for the teleportation to go through. Transferring state via EM waves at the speed of light (300km/s) that still gets you between half a million and a million kilometers distance in 2-3 seconds. Seems like plenty range to not need anything instantaneous.
No. Maybe "relatively instantaneously" would be more accurate. Although if we're considering the concept of teleportation as a science fictional plot device in general, it depends, and even within Star Trek, the transporters worked however the plot required.
Trek style transporters did still "move" some kind of matter stream, though. In one episode, the stream bounced off some clouds when an away team was beaming off of a planet and accidentally created a duplicate of Riker.
> Transferring state via EM waves at the speed of light (300km/s) that still gets you between half a million and a million kilometers distance in 2-3 seconds. Seems like plenty range to not need anything instantaneous.
Notwithstanding the other problems involved, sending only state still requires that state to be transferred into some existing matter at the other end.
Not everyone thinks in terms of Star Trek...
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.
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".
Why is it that we cannot passively observe quantum states? Why does observation necessarily have to be destructive?
It's the star trek transporter version of teleportation for quantum mechanical systems.
It's the star trek
transporter version of
teleportation for quantum
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.
Physical networking infrastructure will still be necessary; teleporting a qbit requires a pre-existing entangled qbit pair in addition to two bits of classical information, so you'll need some method of sending one half of an entangled qbit pair to the recipient. It's okay if this process is lossy, because you can easily generate & re-send an entangled qbit if it gets lost. Once you successfully manage to get the entangled qbit through, you can use it to teleport the qbit you actually want to send (whose state is presumably the product of some long, expensive computation and therefore far too valuable to risk sending via such a lossy channel).
This, once reality (at human scale), will bring an important ethical dilemma since for a short time there will be 2 of the same person, which for all intents and purposes are the same, even more so than cloning. Obviously, after transfer is complete, the source would have to be killed.
For non organic matter this could be great and perhaps the basis of some sort of matter to energy converter (it takes energy to create the duplicate), in time, storing the information of stuff you have transferred in a database can do without the initial step, and simply recreate the stuff.
As with any tech, there is a double edge sword to be mindful of.
Be careful what you wish for then push that teleport button as needed.