Macroscopic QT

[piningforthefjords]

I've started a couple of threads about this topic before, but those were a while ago, and I still have some nagging questions.

1.) If we wanted to quantum teleport something macroscopic, where would scanning come into play? I thought that the whole point of QT was that you don't have to scan whatever it is you want to teleport. Wouldn't the only scanning take place before QT, in order to figure out the configurations and positions of the atoms so that a replica could be made at the destination (let's say the destination has stores of materials that they could use to make identical replicas)? Once the two objects are entangled, don't we just have to measure the quantum state of the object at the source and then send the result of the measurement to the destination? Wouldn't the entire object have one quantum state, as opposed to each atom having a state that must be measured?

2.) I understand that, in all of the experiments done so far in QT, the atoms were at close to absolute zero. For macroscopic objects to be quantum teleported, how low would the temperature have to be? Would you risk converting the object to a Bose-Einstein condensate, or in any other way fundamentally and irreversibly altering the object, by lowering it to a temperature suitable for QT?

3.) I once mentioned that, if scanning was necessary, we could use nanobots that would infiltrate the object (if it was a human, they would go through the bloodstream and blood vessels), but was told that the energy required to scan all the atoms in such a short time frame would create a black hole. How so?

4.) This is kind of related to another thread I recently started, but if we wanted to entangle the two objects, would we have to entangle them atom-by-atom, or could we entangle the entire object? Would we have to keep the two objects close to each other and then send them apart?

[Van Rijn]

3.) I once mentioned that, if scanning was necessary, we could use nanobots that would infiltrate the object (if it was a human, they would go through the bloodstream and blood vessels), but was told that the energy required to scan all the atoms in such a short time frame would create a black hole. How so?

Who told you that? I do remember a discussion where you were trying to map the -exact- positions of all particles in a body over a very short time, and you tried to invoke nanobots to do it. I pointed out that this is impossible: Nanobots would be large compared to what you are trying to measure, they would interact with what they were measuring, they would displace molecules just by being in the body (and there would have to be a lot of nanobots to do a quick, comprehensive scan), they would require energy (fuel) to run and would produce heat, and the faster they run the more heat they would produce. That's no black hole, but you could vaporize a body if you tried to run too many nanobots too fast.

[korjik]

Oversimplifying things a bit, but to teleport a macroscopic object, you would have to know the state of every individual wavefunction involved, which since they are all interacting, is like solving 10²³ equations with 10²³ unknowns. You would also need to do the computation fast enough so that no states would change in the meantime.

This is also why things are cooled when experimented on. It keeps thermal motions from changing the state the particles are in.

Technically, unless things are very specially prepared, you cant BEC a composite macroscopic object. There are alot of fermions in a body, not the least of which would be the ion flows that run your nerves.

[Paul Wally]

Given all the "logistics" involved in this sub-microscopic approach I would rather look at some macroscopic solution to teleportation. Maybe we could transform a whole space-time region containing the object into some kind of transmittable form and then inverse transform it on the other end.

[piningforthefjords]

Who told you that? I do remember a discussion where you were trying to map the -exact- positions of all particles in a body over a very short time, and you tried to invoke nanobots to do it. I pointed out that this is impossible: Nanobots would be large compared to what you are trying to measure, they would interact with what they were measuring, they would displace molecules just by being in the body (and there would have to be a lot of nanobots to do a quick, comprehensive scan), they would require energy (fuel) to run and would produce heat, and the faster they run the more heat they would produce. That's no black hole, but you could vaporize a body if you tried to run too many nanobots too fast.

So what if we just used the nanobots BEFORE the QT in order to determine the position of every atom. In that case, wouldn't we have more time than a small fraction of a second?

I mean, would we even really have to do anything on an atom-by-atom basis, other than the initial scanning to determine where each atom is? And if nanobots prove difficult, couldn't we make do with some sort of 3D ultra-hi-res X-ray or scanning machine?

[piningforthefjords]

Oversimplifying things a bit, but to teleport a macroscopic object, you would have to know the state of every individual wavefunction involved, which since they are all interacting, is like solving 10²³ equations with 10²³ unknowns. You would also need to do the computation fast enough so that no states would change in the meantime.

This is also why things are cooled when experimented on. It keeps thermal motions from changing the state the particles are in.

Technically, unless things are very specially prepared, you cant BEC a composite macroscopic object. There are alot of fermions in a body, not the least of which would be the ion flows that run your nerves.

But isn't the point of QT that we DON'T have to know the state of every individual wave function involved?

[korjik]

But isn't the point of QT that we DON'T have to know the state of every individual wave function involved?

No. You have to know the wavefunctions so that you can make a potential that causes a position operator make the wavefunctions be somewhere else. Otherwise teleportation would occur naturally.

[Van Rijn]

So what if we just used the nanobots BEFORE the QT in order to determine the position of every atom.

Then you're "just" asking for the impossible. You can't determine the position of every atom without interacting with, and therefore changing, the positon of the atoms. Nor is it clear why you're just stopping at the atomic level. As long as you're doing that, wny don't you choose a bit less detail (which would be much easier to achieve)?

I mean, would we even really have to do anything on an atom-by-atom basis, other than the initial scanning to determine where each atom is? And if nanobots prove difficult, couldn't we make do with some sort of 3D ultra-hi-res X-ray or scanning machine?

No. And isn't this just another repeat of the discussion in a prior thread? I'm quite sure I mentioned before, and I think this came up more than once, that any active process will work against what you're trying to do. Your ultra-hi-res X-ray is going to put a lot of energy into whatever it's trying to scan.

[piningforthefjords]

Then you're "just" asking for the impossible. You can't determine the position of every atom without interacting with, and therefore changing, the positon of the atoms. Nor is it clear why you're just stopping at the atomic level. As long as you're doing that, wny don't you choose a bit less detail (which would be much easier to achieve)?

So, what, the molecular level?

[piningforthefjords]

No. You have to know the wavefunctions so that you can make a potential that causes a position operator make the wavefunctions be somewhere else. Otherwise teleportation would occur naturally.

So then why do I hear about people trying to scale up QT to, say, 2 atoms or 4 atoms or a larger (though not anywhere near macroscopic) number? Won't they have to read the states of ALL of those atoms? And will it have to be one-by-one in sequential order or will it be simultaneous?

Also, is there some fundamental limit to computation or data transmission rate that stands in the way?

[korjik]

So then why do I hear about people trying to scale up QT to, say, 2 atoms or 4 atoms or a larger (though not anywhere near macroscopic) number? Won't they have to read the states of ALL of those atoms? And will it have to be one-by-one in sequential order or will it be simultaneous?

Also, is there some fundamental limit to computation or data transmission rate that stands in the way?

if you are talking about a few hundred atoms at near absolute zero, figuring the wavefunctions isnt all that hard. It is when you have to do about 10²⁰ that it is flatly impossible.

Data rate is limited to the frequency of the transmitter. 10²⁰ bits per second is going to be up into the gamma range for a EM transmitter.

[piningforthefjords]

if you are talking about a few hundred atoms at near absolute zero, figuring the wavefunctions isnt all that hard. It is when you have to do about 10²⁰ that it is flatly impossible.

Data rate is limited to the frequency of the transmitter. 10²⁰ bits per second is going to be up into the gamma range for a EM transmitter.

But the exponential growth of computing technology, including quantum computing, should help us find a way around that, right?

[Shaula]

Not really. Better encoding and so on may help a little but for free space comms you are still having to shift so much data that the antenna and power constraints hit you hard. We'd need some serious advances to get around that.

[piningforthefjords]

if you are talking about a few hundred atoms at near absolute zero, figuring the wavefunctions isnt all that hard. It is when you have to do about 10²⁰ that it is flatly impossible.

Why is it flatly impossible?

Data rate is limited to the frequency of the transmitter. 10²⁰ bits per second is going to be up into the gamma range for a EM transmitter.

Couldn't we put the transmitter in space? That way, the gamma rays would get absorbed by the ozone layer.

[piningforthefjords]

Not really. Better encoding and so on may help a little but for free space comms you are still having to shift so much data that the antenna and power constraints hit you hard. We'd need some serious advances to get around that.

What about something other than antennas and transmitters? Surely, there must be some other way to transmit information. Heck, one of the currently planned applications for QT is transmission of information, right?

[Shaula]

Circular argument. In order to QT you need to read the state and transmit it. You cannot use QT to solve this problem.

I did say barring some serious advances. But essentially you are moving into 'this be magic' territory. We need information to get from a to b fast and without huge energy expenditure. Until we find a way around that problem this mechanism for QT is dead in the water.

[Grey]

Piningforthefjords, it is entirely possible that someday we might figure out a way around the technical and physical problems with teleporting macroscopic objects. The point people are trying to make is that it's so many orders of magnitude beyond what we can do that it's not possible to know whether that will be the case. It's a little like asking someone from the stone age about the technical feasibility of sending someone to the moon. It might be possible, but it doesn't look like it, given our current understanding.

[HenrikOlsen]

And like the stone age man who would likely envision getting to the moon as done by building a boat carried by flying swans instead of an Apollo capsule carried by a Saturn V rocket, we have no idea about what breakthroughs would be needed to make it possible.

[Strange]

Flying swans, you say?

[HenrikOlsen]

Yes.

Sorry about the derail BTW.

[piningforthefjords]

Piningforthefjords, it is entirely possible that someday we might figure out a way around the technical and physical problems with teleporting macroscopic objects. The point people are trying to make is that it's so many orders of magnitude beyond what we can do that it's not possible to know whether that will be the case. It's a little like asking someone from the stone age about the technical feasibility of sending someone to the moon. It might be possible, but it doesn't look like it, given our current understanding.

But we're not in the stone age. We're in the space age. We know how to do QT with one atom. Our technology and scientific knowledge is growing exponentially every day. We have scientists working around the clock, and more importantly, we have to motivation and drive to get there.

I don't think it's fair to compare scaling QT up to macroscopic objects to stone age people trying to get to the moon.

[HenrikOlsen]

I don't think it's fair to compare scaling QT up to macroscopic objects to stone age people trying to get to the moon.

It's quite fair because there's as little idea about how to get from A to B in both cases.

[Grey]

But we're not in the stone age. We're in the space age. We know how to do QT with one atom. Our technology and scientific knowledge is growing exponentially every day. We have scientists working around the clock, and more importantly, we have to motivation and drive to get there.

I don't think it's fair to compare scaling QT up to macroscopic objects to stone age people trying to get to the moon.

I disagree that it's an unfair comparison. People in the stone age could travel easily over tens of miles, and with some preparation over hundreds or even thousands of miles. The Moon is just a few orders of magnitude farther away, and the only serious technological issues you have to overcome are to increase your speed sufficiently to overcome gravity and to carry along breathable air for the trip.

Note that when we talk about quantum teleportation with an atom, we're not actually moving an atom from one place to another. We're transferring a quantum state from one atom to another atom somewhere else (usually about a meter away). And even then, it's a very controlled, low energy state, with nothing else around.

So let's imagine scaling this up to actually disassemble a macroscopic object, and then reassemble it somewhere else. What are the steps required? Well, first of all, we have to get better at it. Right now, even the best protocols are only at about 90% successful. And don't think that 95% or 99% or 99.9999% is going to be good enough. Just a single cell has about 100 trillion atoms, and you'd better get nearly all of them right, or you aren't necessarily going to have a functional cell when you're done.

Then, we have to switch from being able to entangle the atoms in the right way for an arbitrary state of any energy, not just a state that we control. It's not clear what will be required here, because the only reason we're able to do this at all right now is precisely because we're carefully controlling the allowed states.

Next, we have to transfer states to multiple atoms at the same time, and this starts getting complicated, because all of the atoms that we need to work with need to already be present at the target. They don't move around in the process, all that gets transferred is the internal state of the atom. So say we want to teleport the state of a water molecule. We'll have to create a water molecule at the destination site, and then entangle each atom of that molecule with the original. What if we want to teleport a protein molecule? Now we'll have to recreate that protein molecule and somehow entangle it with the original. Want to teleport a person? You'd have to reconstruct all of the cells and structures of the person, and then somehow entangle all the atoms of that target with the corresponding atoms in the original.

Constructing a person from scratch, molecule by molecule, is something so far beyond our current capabilities that it's impossible to predict what would be required to do it. Nobody is trying to figure out how to do it, because we don't have the technology to even start.* And even if you know how to construct a person from raw materials (not just any person, of course, it needs to be an exact duplicate down to the atomic level), that doesn't even deal with the issue of trying to keep all the atoms of that duplicate entangled with the original, with all the other atoms moving around.

Technically, though, the quantum teleportation might not be a necessary step here anyway. The exact quantum states of the atoms may not matter. It's entirely possible that if you create an exact duplicate of someone at the atomic level, they'll be indistinguishable from the original even if you don't worry about transferring the quantum states. Certainly it should be sufficient for any inanimate object. But knowing how to do quantum teleportation with one atom doesn't help you with constructing an atom-by-atom duplicate of something in any way. You'd have to first have the duplicate, and then entangle the individual atoms of the original and target, and then you can transfer the quantum states from one to the other.

Quantum teleportation may turn out to be extremely useful for moving information around and quantum computing. However, for moving a macroscopic object from here to there, there's no evidence that it will be of any use.

* And it's not because of lack of application, either. If we had the ability to build body structures at the cellular and tissue level, we'd have essentially solved all our health problems. Have cancer? No trouble, we'll just dismantle all the cancer cells, and then use the raw materials to rebuild normal cells of the same type. Genetic defect? No worries, we'll just send nanobots to every strand of DNA in your body, cut out the problem gene, and then replace it with the normal gene.

[HenrikOlsen]

Have cancer? No trouble, we'll just dismantle all the cancer cells, and then use the raw materials to rebuild normal cells of the same type. Genetic defect? No worries, we'll just send nanobots to every strand of DNA in your body, cut out the problem gene, and then replace it with the normal gene.

Current thinking is instead that we'll take T cells from the patient, tweak them to replicate better and to recognize the cancer cells as an infection then give them back to the patient. Some surprisingly good results have been experienced.

Now back to the OT again.

[Grey]

Current thinking is instead that we'll take T cells from the patient, tweak them to replicate better and to recognize the cancer cells as an infection then give them back to the patient. Some surprisingly good results have been experienced.

Now back to the OT again.

Yes. I learned about this (and some of the crazy methods they're using to make it work!) from xkcd.

[piningforthefjords]

What about non-quantum teleportation? What about the things that you see in Star Trek, where a body is converted to energy and then "beamed" to a destination. What challenges lie in the way of doing that?

[HenrikOlsen]

Immense energies required, E=MC² means a 70 kg human is about 629EJ or about 1.5 time the total energy consumption of 2008; extremely precise measurements required, to the point where they break current theory; extremely precise matter manipulation, to the point where it breaks current theory; without local machinery, which means this is done at a distance or hundreds of miles; error free transmission of extremely large amounts of data, 7*10²⁷ atoms with multiple numbers for each, lets call it 10⁴² bits of information, gamma rays have a frequency of about 10¹⁹ which means it's going to take 10¹⁰ years (twice as long as the Earth existed) just to send the information on one human being even if you did it with gamma rays.

Several of these points are at the "no path ahead" type where current understanding of the universe gives absolutely no clue to how it could be done.

[piningforthefjords]

So, as we all know, scientists at CERN recently found that some neutrinos APPEAR to travel a bit faster than the speed of light. If it turns out not to be correct, and that relativity has been violated, would this move us any closer to macroscopic teleportation, either classical or quantum? Would it make technologies like it possible?

[piningforthefjords]

I guess what I'm wondering is the following, and I would really appreciate some input.

If the recent developments at CERN end up being true (i.e. it turns out that something CAN travel faster than light), then what's to stop us from communicating faster than the speed of light? All this time I've heard that one of the limitations of QT is that information can't be transmitted faster than light. Could this prove that wrong?

Also, if it turns out that the speed-of-light-limit is false, then could that also mean that other barriers to teleportation of macroscopic objects could also prove to be surmountable?

How long before we find violations of the HUP or the second law of thermodynamics? Those are considered fundamental limitations, too, just like the speed of light may have been.

[Shaula]

Neutrinos are not suited for communication so you'd need to find out that whatever was causing this was due a more generalisable mechanism.

All the rest of your questions are basically: "Who knows?" - the thing about the next model is that we don't know anything about it yet. I'd say that none of the limitations raised so far are likely to go away. They are engineering or physical limits that have been probed extensively, so any effects would have to be small and therefore probably unusable. Of course there could be a totally different way to do this that the new theory would cover but as I said - we have no idea what that theory would allow or disallow.