FTL communication

[ibeinsane]

What you are describing is Quantum Cryptography and quantum key distribution. This is currently in use in the world for secure communications, ie the Chinese are currently building a 2'000 km version of this which requires the transmission of photons through fibre optics. See Nature 492, 22–25; 2012 for details of a similar for LEO comms. This is for high security communications.

Although this has grounding with quantum entanglement is not communications via entangled pairs.

[ibeinsane]

The paper described the manipulation of atoms into different energy levels of Cesium using laser excitement with 14 pairs. There is no winning on this forum, you cite a non peer reviewed paper and everyone claims its not peer reviewed, you cite a reviewed paper and everyone claims there isn't enough detail in the abstract.

For all of you who can't access papers here is a scientific American report on the paper. It cites

Monz and his colleagues encoded information onto a string of trapped calcium atoms, using two energy levels of the atom to represent 0 and 1. Using lasers to manipulate the atomic qubits, the group set the entire ensemble into superpositions of 0 and 1â€â€in other words, each qubit is in a sense both a 0 and a 1 until it is measured, at which point it is forced to settle on being one or the other.'

http://blogs.scientificamerican.com/observations/2011/04/05/physicists-entangle-a-record-breaking-14-quantum-bits/

It also points out the limitations in the capability.

I suggest you undertake your own research of papers before dismissing posts as making things up and provide clear evidence to what you are suggesting.

[N_las]

What you are describing is Quantum Cryptography and quantum key distribution. This is currently in use in the world for secure communications, ie the Chinese are currently building a 2'000 km version of this which requires the transmission of photons through fibre optics. See Nature 492, 22–25; 2012 for details of a similar for LEO comms. This is for high security communications.

Although this has grounding with quantum entanglement is not communications via entangled pairs.

Quantum communication has nothing to do with transmitting information using entanglement. It basically encompasses just quantum teleportation and quantum cryptography

The paper described the manipulation of atoms into different energy levels of Cesium using laser excitement with 14 pairs. There is no winning on this forum, you cite a non peer reviewed paper and everyone claims its not peer reviewed, you cite a reviewed paper and everyone claims there isn't enough detail in the abstract.

For all of you who can't access papers here is a scientific American report on the paper. It cites

Monz and his colleagues encoded information onto a string of trapped calcium atoms, using two energy levels of the atom to represent 0 and 1. Using lasers to manipulate the atomic qubits, the group set the entire ensemble into superpositions of 0 and 1â€â€in other words, each qubit is in a sense both a 0 and a 1 until it is measured, at which point it is forced to settle on being one or the other.'

http://blogs.scientificamerican.com/observations/2011/04/05/physicists-entangle-a-record-breaking-14-quantum-bits/

Those papers have nothing to do with communicating through entanglement.

Edited September 26, 2014 by N_las

[ibeinsane]

I hope this abstract from the paper provide a clearer understanding.

http://www.nature.com/nphys/journal/v6/n5/full/nphys1603.html

[N_las]

I hope this abstract from the paper provide a clearer understanding.

http://www.nature.com/nphys/journal/v6/n5/full/nphys1603.html

You are just posting papers that report about creating large entangled quantum systems. What is the relevanz of that? That has nothing to do with your version of "quantum communication"

[ibeinsane]

Those papers have nothing to do with communicating through entanglement.

Ok, now your just trying to wind me up, these show the creation and manipulation of states of entangled pairs. Although not directly showing communication across distances, your earlier comments stated this was the reason that communication through quantum entanglement was not possible as only random numbers can be generated.

I provided the reviewed information that your basis for dismissing the possibility has been explored experimentally.

'

[ZetaX]

Yes, you can entangle A and B and then B with C (and so on), and then forcing A into a know state will force B and therefore also C. But nowhere did you get to choose the state of A (or B or C)!

[ibeinsane]

The paper cited showed experimental groups manipulating the state of one of the cubits by laser excitation within an entangled system. This is the first step of a far off ability if at all practically possible and I did not claim to be a functional communication method as of yet, neither is it possible to currently transmit encryptions keys in this fashion.

[N_las]

Ok, now your just trying to wind me up, these show the creation and manipulation of states of entangled pairs. Although not directly showing communication across distances, your earlier comments stated this was the reason that communication through quantum entanglement was not possible as only random numbers can be generated.

I provided the reviewed information that your basis for dismissing the possibility has been explored experimentally.

'

I am sorry if I wasn't clear. Of course you can create and manipulate entangled quantum states. But that doesn't has anything to do with the reason why you only can transfer random numbers:

Imagine we have a perfect set of millions of entangled particles. I sit at end A, and you sit at end B. We can even manipulate the quantum state of this entangled system. But how would I send information to you? There just isn't a way. How would you do it? Thats not just a technological limitation. You can imagine perfect technology.

If I measure something about the system, I may be able to predict what you will get if you make the same measurment. But how can we make communication with that?

If I measure "1", I may be able to predict that you will measure "0". If I flip my bit (just on paper) after the measurment, we will have both "0". But that is random. We could just as easily have both "1". So we have both the same random number "0" or "1". Thats all "communication" that can be done. There is no information involved.

Edited September 26, 2014 by N_las

[ibeinsane]

I understand where you are coming from although I dispute the complete randomness as it is probabilistic not quite random, not important in what has been said but a little more relevant below.

I suppose my argument was that the manipulation of a cubit is the manipulation of a quantum state without its collapse which would infer that the manipulation of an entangled pair in a quantum state should be possible although I cannot find a direct reference for this. I can only find reference to alteration of a state without collapsing a function tentatively here: http://www.nature.com/nphys/journal/v10/n3/full/nphys2881.html

Although in response to your question as a thought process.

The papers do show they can create entangled particles (cubits) of a specified state by manipulation with lasers etc. This could, for arguments sake create a whole system of entangled 1's (lets use spin for this example as they are opposite for entangled pairs). If I then measure all of the bits at my end I collapse the wavefunction and the particles cease to be entangled.

If you then measure your system after I have collapsed the wave function then you should read a random (probabilistic) collection of 1's and 0's (or spins).

With enough data it would be possible to determine the difference between a system of entangled 1's and a system of random states.

I am still thinking this through and it is at odd's with my own understanding of quantum mechanics but I cannot recall the wavefunction persisting after collapse from one side.

Any thoughts? Or have I misunderstood the collapse of the wavefunction?

[rtxoff]

Please have a look at this experiment. Back in time signaling is already reality it's just awaits confirmation from other labs.

[ZetaX]

Apart from this thing looking completely unscientific (font, power point, ...), it does not contain any explaination on how this supposedly work (maybe the link does, but I will not open that PPP; give an actual paper), just a claim it does time travel. Really, don't post such crap.

[N_las]

The papers do show they can create entangled particles (cubits) of a specified state by manipulation with lasers etc. This could, for arguments sake create a whole system of entangled 1's (lets use spin for this example as they are opposite for entangled pairs). If I then measure all of the bits at my end I collapse the wavefunction and the particles cease to be entangled.

What do you mean by "entangled 1's" ? How can we know that they are all in state 1? The state is only determined by a measurment, so before we measure we can't possibly say that they are in state 1.

If you then measure your system after I have collapsed the wave function then you should read a random (probabilistic) collection of 1's and 0's (or spins).

With enough data it would be possible to determine the difference between a system of entangled 1's and a system of random states.

So what you are saying is, that by manipulating the particles at my end, I can somehow change the probability of what you are measuring? Thats not possible.

Lets imagine we have a single pair of entangled particles (A (mine) and B (yours)). If I would measure spin-up, then you will measure spin-down. But that isn't determined yet. If you would measure at your side, you would have a 50/50 chance.

So the system can be described as:

S = 50% [A-up;B-down] + 50% [A-down;B-up]

(That is not the standart notation used in QM)

Now I can do some manipulation at my side. I shoot at it with another particle ©. Say C has a chance of 75% spin-up, and 25% spin-down. Lets just invent some rules here: If a collision happens between particles with even spins, they will flip their spin. If a collision happens between uneven spins, they will keep their spin.

After their collision, the system can be described as:

S = 12.5%[A-up;B-up,C-up] + 37.5%[A-down;B-up,C-up] + 37.5%[A-down;B-down;Cdown] + 12.5%[A-up;B-down;C-down]

As one can see, the system is now changed by my manipulation.

If you make measurments on the System S, you can only get a value for the spin of B. And from the describtion of S after the collision, we see that your probablity of measuring spin-up or spin-down is exactly 50/50.

It doesn't matter what manipulation I make for the System. The mathematical rules behind quantum mechanics won't allow for any different result, I can't change your probability of which spin you measure, it doesn't matter which manipulation I make.

Edited September 26, 2014 by N_las

[N_las]

Apart from this thing looking completely unscientific (font, power point, ...), it does not contain any explaination on how this supposedly work (maybe the link does, but I will not open that PPP; give an actual paper), just a claim it does time travel. Really, don't post such crap.

They just describe an experiment, they don't have any measurments (at least not in the ppp). It is far from "already reality". The supposed mechanism is based on ignorance about quantum mechanics.

[Error404brain]

if u have instrument precise enough, just 2 coin would be enough.

Since gravity is instantaned (for what we know).

[N_las]

if u have instrument precise enough, just 2 coin would be enough.

Since gravity is instantaned (for what we know).

Disturbances in spacetime travel at the speed of light. So gravity is not instantaneous, and we have known that for a hundred years.

[magnemoe]

They just describe an experiment, they don't have any measurments (at least not in the ppp). It is far from "already reality". The supposed mechanism is based on ignorance about quantum mechanics.

Or more probably waves, first light in fibre optic don't travel at c but a bit slower.

Now I wonder how fast electron tunnels trough an tunnel diode?

And no I don't think its some sort of sensor who stop transferring information faster than light. If we find some theoretical sound method of doing it it would shatter.

I see the coupling faster than light== time travel as false. Or more like someone is putting to many layers on top of relativity theory like other do with the bible.

And yes lots of it sounds more like God or gamemaster crack down on exploits

No traveling between stars will probably be hard and pretty much be reserved for the ones doing it for the emperor, the race or the fanged god (its important to have good reasons )

[Heimdall5008]

Regarding Birgit Dopfer's experiment linked some pages above:

I've done a similar thought experiment in university. So even if it is not possible to send a string of bits (as it was done in this experiment), it should at least be able to send exactly 1 bit (e.g. a timer or alarm signal). This could be useful for a superlumious warning of a solar flare or something like this. This 1 bit should be challenging enough with our technology (high failure rate, therefore many repetitions required to get a statistical significant statement) on anyway longer than lab distances. But with good enough equipment it may be possible to get a superluminoius communication channel that could transmit short meassages (the longer the message the longer the distance between sender and receiver has to be to give you any advantage to a classical channel).

I have no idea why this seems to work (against the statement that information cannot travel faster than light). My best idea to this was that each experiment itself has less information than 1 bit (the smallest information unit). Only with statistical effects of some (many) repetitions you get that information summed up to 1 bit (or more). A bit like the difference between signal velocity and group velocity (the latter can get to superluminous speeds, but is no "real" velocity).

[heretofore]

Given the known constraints, you're not going to get FTL communication ability without warping spacetime. Waiting for proof-of-concept on that one. I can imagine only two other alternatives. Both rely on black box stuff. One requires that we more fully understand the underlying dimensions of the quantum world and somehow figure out how to make shortcuts. The other is is we discover that we're in a simulation, and the simulators contact us, and afford us a cheat.

[ibeinsane]

So what you are saying is, that by manipulating the particles at my end, I can somehow change the probability of what you are measuring? Thats not possible.

If you make measurments on the System S, you can only get a value for the spin of B. And from the describtion of S after the collision, we see that your probablity of measuring spin-up or spin-down is exactly 50/50.

It doesn't matter what manipulation I make for the System. The mathematical rules behind quantum mechanics won't allow for any different result, I can't change your probability of which spin you measure, it doesn't matter which manipulation I make.

\Indeed you are correct.

After looking again at the papers who show manipulation of entangled qubits, the premise for which I surmised it may be possible to changed the state of an entangled pair, I see I misread. They actually manipulate the entangled qubits into an energy state to allow 2 outcomes, not to be 1 of the 2 outcomes, this allows them to set the whole qubit to a single value of "1's" or "0's". Obviously not the manipulation I originally thought.

I was obviously still asleep during the lecture when Alice and Bob discussed this.

As for the probabilities you are correct as I misinterpreted the collapse of the entanglement as a collapse in the 'system' which would the require separate and independent probabilities for each set of entangled pairs. This is incorrect as the observation of one of the pair sets the outcome for the other, the pair as a system constitute the known quantum state, not the individual within the pair.

I'll go back to my 1D structures and stop arguing quantum theory.

[Alchemist]

I still don't see the paradox. Let's just compare light-speed and FTL communication with a rover on Mars (let's assume the distance to be 15 light minutes)

Light speed:

What happens for observer on Earth:

Signal is sent to the rover. 30 minutes later we observe the rover receiving the signal, fulfilling the order and sending the confirmation which is received in this very moment.

What happens to the observer on Mars:

The control center is observed sending the message which is immediately received by the rover. It fulfills the order and sends the confirmation. 30 minutes later the control center is seen receiving the message.

Instant FTL:

What happens for observer on Earth:

Signal is sent to the rover. After time it takes the rover to turn we receive the confirmation. 15 minutes later we observe the rover receiving the signal, fulfilling the order and sending the confirmation.

> we receive the confirmation before the rover did it in our frame of reference. - the signal comes from 15 minutes of rover's future

What happens to the observer on Mars:

The rover receives the command. It fulfills the order and sends the confirmation. 15 minutes later the control center is seen sending the command and then receiving the message.

> the command is received from 15 minutes in command center's future.

where can you really get something to your own past here?

[rtxoff]

nowhere, people just don't want it to be true

[N_las]

Where can you really get something to your own past here?

Imagine you have two completely seperate events happening: Event1 on Earth and Event2 on Mars. Let's assume that earth and mars are stationary, and at a distance of 15 light-minutes (in our reference frame).

If we observe Event1 here on earth and 15 minutes later we observe Event2 on Mars, we can say: "From our point of view, it seems that both events happend at the same time. We observe Event2 15 minutes later, but that is just the travel time of the signal."

Now imagine a 3rd observer that passes Event2 at a near light speed (relative to Mars, Earth, our reference frame). He observes Event2, and he is really close to mars, so the signal delay between Event2 and him is very very small. He might think: "Event2 is happening right now".

If you ignore special relativity, you might think that he will observe Event1 15 minutes after that, and Earth is at a 15 light-minute distance. But depending on his velocity he can see a comletely different distance, and a completely different time intervall before observing Event1.

I havent done the math, but lets assume he sees a distance of 10 light-minutes, and a time intervall of 5 minutes. So from his point of view, even if he takes the signal delay into account, Event1 happed 5 minutes before Event2.

Depending on his velocity, he might see the opposite, that Event1 happend 5 minutes after Event2. Thats the thing about relativity. You can't say that two distant events are happening at the same time. Even if you think they happen at the same time (taken signal delay into account), for a different observer they can happen at different times, or 2 events that happen at different times for you may happen at the same time for a different observer. The extrem case is if you would travel at the speed of light. Then ALL events seem to happen at the same time.

Only to events that happen at the same place can be "objectivly" happen at the same time, because every observer will agree on that.

Now whats happen if we use FTL signals. Lets say that communication with this machine is instant for the reference frame of the sender. If we say that Event1 was the sending of the instant com-signal, and Event2 was the receiving of the instant com-signal on mars, from our point of view both things happen at the same time.

In a reference frame of a 3rd observer, Event2 can happen before Event1. If he uses the same FTL communication technology, he may send us a picture of Event2. But if the FTL signal is instant from the reference frame of the sender, then the people on Earth will receive this message at a point in time before Event1.

So with FTL communication, there is a possible setup that allows us on Earth to receive information about Event2 before we cause Event1. If we send an instant message to mars, we can receive it back on earth before we send it.

[rtxoff]

With this logic there is no 3rd. observer necessary, earth will recieve an answer from the rover before the command is sent and i honestly don't think that is possible however i also think superluminal communication is possible in a way or another. Maybe i am a mad unscientific man because of that but i don't care, there must be a way.

[N_las]

With this logic there is no 3rd. observer necessary, earth will recieve an answer from the rover before the command is sent and i honestly don't think that is possible however i also think superluminal communication is possible in a way or another. Maybe i am a mad unscientific man because of that but i don't care, there must be a way.

You can skip the third observer only if the receiver on Mars has a very high velocity relative to Earth.