Traveling without moving: Quantum communication scheme transfers quantum states without transmitting physical particles

March 10, 2015 by Stuart Mason Dambrot feature
Figure 1 | Quantum control device for the passing or blocking of the incident single photon with the frequency ω. A control atom and a mesoscopic Rydberg atomic ensemble are stored in two separate trapping potentials, and the ensemble forms a superatom with the collective ground state |G> and the Rydberg state |R>. The single atom controls the transmission properties of the ensemble by Rydberg dipole interaction. The photon will be absorbed by the ensemble for the control atomic state | g>, and will pass through the ensemble for the control atomic state | r >. Credit: Guo, Q., Cheng, L.-Y., Chen, L., Wang, H.-F. & Zhang, S. Counterfactual quantum-information transfer without transmitting any physical particles. Sci. Rep. 5, 8416; DOI:10.1038/srep08416 (2015). Copyright © 2015, Rights Managed by Nature Publishing Group. Licensed under CC BY 4.0.

(Phys.org)—While Einstein considered quantum entanglement as "spooky action at a distance," and those who fully accept entanglement acknowledge it to be counterintuitive, current entanglement-based quantum communication schemes for transferring an unknown quantum state from one place to another require classical transportation of particles between sender and receiver. Now consider this: Recently, scientists in China at Harbin Institute of Technology, Yanbian University and Changchun University demonstrated what is known as a counterfactual approach in which quantum information can be transferred between two distant participants without sending any physical particles between them. The researchers accomplished this by entangling two nonlocal qubits with each other without interaction – meaning that the present scheme can transport an unknown qubit in a nondeterministic manner without prior entanglement sharing or classical communication between the participants. Moreover, the scientists state that their approach provides a new method for creating entanglement that allows two qubits to be entangled without interaction between them.

Prof. Shou Zhang discussed the paper that he and his colleagues published in Scientific Reports. "There's a long-held assumption in the classical information field that information transfer requires physical particles to travel between sender and receiver – an assumption first challenged in 2013 by Hatim Salih and his colleagues1," Zhang tells Phys.org. By using the so-called chained quantum Zeno effect, the 2013 paper showed how information can in fact be transferred between two locations without any physical particles traveling between them. (In the quantum Zeno effect, time evolution caused by quantum decoherence in quantum systems is suppressed by, for example, continuous observation or measurement, interaction with the environment, or stochastic fields. In a chained quantum Zeno effect, a series of secondary splitter/detector loops ensure that there is never a significant probability of decoherence.) "This mind-boggling and highly counterintuitive communication protocol inspired us to think whether quantum information can be transferred counterfactually," Zhang adds, "so in fact, our present scheme can be considered as an incremental extension of Salih's work from classical bit to quantum bit."

"In quantum information science," Zhang continues, "the minimum information unit is quantum state-encoded qubit. However, to date, schemes for the transfer of an unknown quantum state required physical particles to travel – for example, quantum teleportation needs prior entanglement sharing and classical communication, and both entanglement sharing and classical communication cannot be done without transmitting physical particles. In our scheme, entanglement sharing and classical communication are not needed."

In short, existing quantum-information transfer schemes require a physical medium, and it was unclear if quantum information can be transferred without transmitting any physical particles – but this paper suggests that it can. To achieve this counterfactual scheme by entangling two nonlocal qubits with each other without interaction, Zhang says that their main challenge was determining how to place the obstructing object in Salih's scheme in an unknown quantum superposition state of presence and absence. "Entanglement is basic resource for many nonlocal quantum information tasks," Zhang notes. "However, it's well known that distant separable states cannot be entangled only by means of local operations and classical communication. Generally, people introduce nonlocal interaction by entanglement swapping or transmitting a mediating particle between distant quantum nodes. Interaction-free measurement provides a new way to create entanglement, and so, albeit inconceivably, two qubits can be entangled without interaction."

Zhang notes that there were also several challenges in the experiment in realizing the scheme by using a photon and a Rydberg atom assisted by a mesoscopic atomic ensemble, such as trapping atoms and the ensemble's coherent time. (A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number, meaning that the electron has higher potential energy and is therefore less tightly bound to the nucleus.) "Given that this paper is a theoretical work, and these technical challenges have been well researched in the existing literature, we only consider the ideal case in the paper."

The key component in this work, Zhang tells Phys.org, is the quantum version of the obstructing object. "In fact, any atom with two energy levels resonant with the photon's frequency can be used to act as the quantum obstructing object to control the passing or absorption of the photon, but the coupling between a single atom and a photon is so weak that the scheme cannot be achieved with high probability. The present scheme uses a single Rydberg atom to control the atomic ensemble via Rydberg dipole blockade." A Rydberg dipole blockade, which results from the interactions shifting the energy levels of the atoms, can be used to inhibit transitions into all but singly excited collective states – and thereby to manipulate quantum information stored in collective states of mesoscopic ensembles.

Figure 2 | Schematic of interaction-free nonlocal entangled state generation. N unbalanced beam splitters BS form a tandem Mach-Zehnder-type interferometer with the two optical paths 0 and 1. The ensemble is inserted in the path 1, and the single photon enters the interferometer from the path 0. M is normal mirror. Credit: Guo, Q., Cheng, L.-Y., Chen, L., Wang, H.-F. & Zhang, S. Counterfactual quantum-information transfer without transmitting any physical particles. Sci. Rep. 5, 8416; DOI:10.1038/srep08416 (2015). Copyright © 2015, Rights Managed by Nature Publishing Group. Licensed under CC BY 4.0.

"The Rydberg dipole blockade can block transitions of more than one Rydberg excitation in mesoscopic atomic ensembles," Zhang explains. "The combined system of the single atom and the atomic ensemble forms a quantum control device to control the passing or absorption of the photon. The ensemble is initially in the collective ground state; if the single atom is in the Rydberg state, the photon can pass through the ensemble, while if the single atom is in the ground state, the photon will be absorbed by the ensemble. Therefore, the combined system acts as a quantum obstructing object, and the passing or absorption of the photon depends on the quantum state of the single atom. By inserting the quantum obstructing object in a nested Mach-Zehnder interferometer as shown in Figure 3 in our paper, and then connecting many such interferometers in series, the quantum state of the single atom will appear on the path qubit of the photon after the photon passes through the interferometer series and the sender measures his atom." (A Mach–Zehnder, or MZ, interferometer is a device used to determine the relative phase shift variations between two collimated beams derived by splitting light from a single source.)

What's key is that during the entire process, the photon did not enter the channel between sender and receiver: As long as the photon passes through the channel, it will be absorbed by the ensemble if the control atom is in the ground state – but if the atom is in the Rydberg state, the photon will be absorbed by the detector. In this way, an unknown quantum state can be transferred between two distant participants without any physical particles traveling between them.

"The advantages of using the combined system," Zhang explains, are twofold: the coupling strength of the photon with the quantum obstructing object is greatly enhanced; and the individual addressing of an atom is not required. In principle, as long as the quantum obstructing object can be implemented, this scheme is universal for other physical systems of quantum information processing, such as trapped ion systems, superconducting quantum systems and quantum dot systems."

Unlike typical teleportation, the present scheme can transport an unknown qubit between two distant participants in a nondeterministic manner. "Typical teleportation can teleport an unknown quantum state perfectly by using subsequent local operations. However," Zhang points out, "in the last step of the present scheme, the sender will obtain two measurement results of the single atom state, and the recipient can obtain the teleported state perfectly only if the sender's measurement result is a Rydberg state. If the sender's measurement result is , the quantum state the recipient receives has a phase flip error compared with the teleported state. Hence, the success probability is 50%. On the other hand, if the recipient wants to obtain the quantum information deterministically, the sender only needs to send one bit of information – that is, single-qubit detection results – to the recipient for the transfer of one qubit. However, in the one-qubit teleportation procedure, two bits of classical communication – that is, Bell-state measurement results – are required."

Regarding the implications and limits of their approach, Zhang says that the present scheme requires the single go through a large number of cycles in the nested interferometer, so the main limits of the scheme are the distance of the two parties and the coherent time of the Rydberg atom. "In principle, however, quantum information can be transferred without entanglement sharing or classical communication between the two parties regardless of the physical distance separating them." However, he emphasizes that since the coherent time of the atom is finite in practice, the counterfactual quantum-information transfer can be only implemented over a limited distance.

Figure 3 | The nested Mach-Zehnder-type interferometer shared by two distant participants, sender Bob and receiver Alice. The interferometer in Fig. 2 as an inner interferometer is nested in one arm of an outer Mach-Zehnder-type interferometer. Connecting M such outer interferometers in series, we can implement counterfactual nonlocal entangled state generation and quantum state transfer. The two optical paths of the outer interferometer are labeled as a and b, and the two optical paths of the inner interferometer are a0 and a1. OD: optical delay line used to match the optical path lengths of the different paths of the interferometer. D: conventional photon detector used to absorb the photon exits from the output port of a1. Credit: Guo, Q., Cheng, L.-Y., Chen, L., Wang, H.-F. & Zhang, S. Counterfactual quantum-information transfer without transmitting any physical particles. Sci. Rep. 5, 8416; DOI:10.1038/srep08416 (2015). Copyright © 2015, Rights Managed by Nature Publishing Group. Licensed under CC BY 4.0.

"Theoretically," Zhang acknowledges, "a galactic or intergalactic internet may be possible based on the present scheme, which would require a so-called long-arm intra- or intergalactic interferometer and a quantum obstructing object with very long coherent time. Obviously, however, it's currently unpractical to construct a long-arm interferometer, and there is no known quantum state with such a very long coherent time."

Despite the effect of the imperfections mentioned in the paper, Zhang tells Phys.org that the key component in the experimental system indicating that their scheme may be feasible using current technology is the combined system of a single atom and a mesoscopic atomic ensemble – specifically, the development of the cold Rydberg gas with alkali-metal vapor. "Moreover," he adds, "the remaining elements in the scheme are the most common optical elements found in the laboratory."

Moving forward, Zhang notes that the scientists are now researching the deeper mechanism behind the counterfactual quantum-information transfer, which he says may involve the foundation of quantum mechanics. "In addition, using the basic idea of the scheme, many nonlocal quantum information tasks could be achieved. We may develop other counterfactual quantum information protocols, such as quantum cloning or quantum algorithms."

In closing, Zhang says that the present scheme provides a new way for nonlocal processing, so it may lead to a quantum network that does not require physical particle transmission. "We also hope the present scheme can be realized in a physical experiment. On the other hand, the deeper mechanism behind the counterfactual scheme has not been revealed, which may well excite people's interest in the fundamental of quantum mechanics, such as quantum interference and wave-particle duality."

Explore further: High-fidelity photon-to-atom quantum state transfer could form backbone of quantum networks

More information: Counterfactual quantum-information transfer without transmitting any physical particles, Scientific Reports (2015) 5:8416, doi:10.1038/srep08416

Related:

1Protocol for direct counterfactual quantum communication, Physical Review Letters (2013) 110:170502, doi:10.1103/PhysRevLett.110.170502

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arom
Mar 10, 2015
This comment has been removed by a moderator.
dirk_bruere
5 / 5 (4) Mar 10, 2015
"What's key is that during the entire process, the photon did not enter the channel between sender and receiver"

In this universe.
indio007
1 / 5 (5) Mar 10, 2015
This is near field coupling nothing more. Even Planck gave up on trying to characterize it mathematically.
hillmeister
not rated yet Mar 10, 2015
Awesome news! This is true quantum teleportation, unlike currently where you need to mix it with classical mechanics.
We will eventually reach a point where we can teleport to distances non locally just as good as current teleportation.
Spockbob
1 / 5 (3) Mar 10, 2015
but particles larger than a photon or electron may never happen.
hiranyu
5 / 5 (7) Mar 10, 2015
If this sort of research eventually leads to practical communication devices it would explain why SETI has found squat.
rufusgwarren
1 / 5 (4) Mar 10, 2015
Show the affects of the atomic structure with only the coulomb force, then add any local variable fields, now apply an outside field to create any field event among the chaos, or simply select a resonant mode. even modulate this to create any event!

Didn't a team just show us exactly that!

Foundation of quantum, mechanics! Didn't Maxwell give us charge? You just forgot to redefine mass!
rufusgwarren
1 / 5 (5) Mar 10, 2015
A photon is an event, not a particle, seems like a particle to the blind, really? Particles create the waves, and the local field. All you get is E and variations there-of, no matter how you curl it, but you don't get to change back to a particle. Playing it backward is an interesting idea, should be the same from any axis? Only if nothing changes but the sign!
Dethe
1 / 5 (1) Mar 10, 2015
Quantum communication scheme transfers quantum states without transmitting physical particles
A notoriously known quantum coral (first observed in 1993) may serve as an example of dislocation of physical state without actual transfer of physical particle. The above experiment just serves as another confirmation of the above paradigm.
Dethe
1 / 5 (4) Mar 10, 2015
BTW Some psychic phenomena or homeopathic effects of seemingly pure water could be explained with teleportation of physical state of objects without actually moving them, for example the molecules adsorbed on the walls of vessel into volume of water. It was already observed that the complex charged DNA molecules can affect another molecules at distance.
Whydening Gyre
1 / 5 (1) Mar 10, 2015
[So... they're not actually TRANSMITTING, just transferring info, and creating a - doppelganger?!?
PhysicsMatter
4.8 / 5 (4) Mar 10, 2015
Another rather confusing post about so-called quantum entanglement. I hope that they got something but Chinese quantum "explanation" of the effect seems to be far fetched. Passing information with no material transfer is not a quantum effect like passing gravitational information from Moon to Earth resulting with ocean tides is not a quantum effect either but achieved by no matter (mass) transfer we know of.

Very instructive take of quantum theory and its misinterpretations can be found at:
https://questforn...-quanta/
rufusgwarren
not rated yet Mar 10, 2015
Quantum communication scheme transfers quantum states without transmitting physical particles
A notoriously known http://www.law-c....03_1.jpg (first observed in 1993) may serve as an example of dislocation of physical state without actual transfer of physical particle. The above experiment just serves as another confirmation of the above paradigm.

Physically, there could exist an infinitely fast moving wavelet with an infinite wavelength, the infinities are relative. Hence, piggy back. So the chinese may be correct, a quantum mechanical phenomenon always has a realistic explanation.

But I will hold my breath, or not!
fixitup
not rated yet Mar 10, 2015
I think Seth Shostek's radio telescope array might be missing some pertinent equipment.........
koitsu
not rated yet Mar 10, 2015
Much respect to the author for the Jamiroquai reference. Clever devil.
yks
5 / 5 (1) Mar 11, 2015
Is this instantaneous or superluminal communication (like the fictional Ansible)?
AmritSorli
not rated yet Mar 11, 2015
because space itself is a direct information medium of quantum entanglement
http://www.degruy...14-5.xml
antialias_physorg
5 / 5 (6) Mar 11, 2015
Is this instantaneous or superluminal communication

Careful. They are talking about quantum information. Not classical information. Difference is: you can use classical information to transmit a message (what we imagine when we colloquially talk about 'passing on information to someone').
Quantum information is the passing on of a quantum state. This cannot be used for (the colloquial form of) information transmission.

As it is stated (repeatedly) in the article:
The researchers accomplished this by entangling two nonlocal qubits with each other without interaction – meaning that the present scheme can transport an unknown qubit in a nondeterministic manner without prior entanglement sharing or classical communication between the participants.

The key word here is "unknown". You cannot pass (classical) information of you don't know what you are encoding on the sending end.
antialias_physorg
5 / 5 (3) Mar 11, 2015
To put this another way: The speed of light isn't just the cosmic speed limit of light. On a more fundamental level it is the cosmic speed limit of classical information transmission.

(i.e. if we ever do find a way to break that barrier then that would mean the end of Relativity)

While I do enjoy these word plays and quotations ("travelling without moving"...right out of the Dune novels by Frank Herbert. It's not a jamiroiquai reference. He ripped it from the novels, too), they nevertheless are an endless source of confusion to the layperson.
jposterman
not rated yet Mar 11, 2015
You've done fantastic experimentation! Your works helps validate the science in my sci-fi books! You're pioneers of change and scientific advancement. Great job!
swordsman
1 / 5 (1) Mar 11, 2015
This is the electromagnetic effect on matter exactly as Planck described it in presenting his famous quantum theory.
Bill Gaede
1 / 5 (2) Mar 11, 2015
Mr. Zhang would do well in learning the basics of Physics before publishing irrational explanations such as 'medium-less' entanglement. Spooky action-at-a-distance is not so spooky as it seems to the mechanics and other mathemagicians who propose to do 'physics' without mediators.
.
https://www.youtu...iR1gjcEs
.
.
.
pepe2907
not rated yet Mar 11, 2015
Physically, there could exist an infinitely fast moving wavelet with an infinite wavelength, the infinities are relative

Problem with such wavelet, even if theoretically possible, is that it would have infinitesmall energy /density/, and any communication as we know it up to now is based on some, even if small, energy transfer /even with the most sensitive detectors we still need some energy to be passed/.
So, with instantaneous information transmission forget about any waves... huh.
Dethe
1 / 5 (3) Mar 11, 2015
you can use classical information to transmit a message (what we imagine when we colloquially talk about 'passing on information to someone'). Quantum information is the passing on of a quantum state. This cannot be used for (the colloquial form of) information transmission.
This is not true and it's also denial of the whole idea of quantum computers for instance. Currently it's already accepted, that the quantum information can be shared in superluminal speed - this is just the aspect, in which it differs from this classical one. This quantum information is just not fully deterministic, which makes no problem in most of practical applications.
Dethe
1 / 5 (5) Mar 11, 2015
Usually I'm explaining this controversy with water surface analogy of board dividing the pool of water into two halves. Usually the information spreads along water surface with speed of surface ripples, which corresponds the speed of light in this analogy. But the board prohibits the spreading of these ripples, it doesn't prohibit the spreading of underwater sound waves though. So if we make a splash at one half of pool, some minute portion of energy will still teleport itself across the board, but with speed which will be much higher, than the speed of the surface ripples. For observer of this energy behind the board the sound waves will spread along water surface from many directions at the same moment, so he may not be able to localize the exact position of the source of splash behind the board - this indeterminism is the price for "superluminal" information transfer in this analogy.
pepe2907
5 / 5 (4) Mar 12, 2015
Dethe, your "explanation" with some "underwater" sound waves /energy transfer is a complete physical nonsense unless you can present it as a part of a complete theory of "hyperspace" /to take the role of your "underwater"/.

To say it's "already accepted" and to cite a publication in Extremetech as a proof of that is... well, lets just say it's not peer reviewed...

As much as I am informed up to now any form of "quantum" communication actually involves transmission of a physical/electromagnetic signal, possibly with the exception of the case presented in this article - it's what makes the case unique and is specifically pointed in the article.
katesisco
1 / 5 (1) Mar 15, 2015
FOURTH UNCLE IN THE MOUNTAIN by Quang Van Nguyen and Marjorie Pivar

St. Martin's Griffin

I would suggest water has a memory.
Dethe
1 / 5 (1) Mar 15, 2015
your "explanation" with some "underwater" sound waves /energy transfer is a complete physical nonsense unless you can present it as a part of a complete theory of "hyperspace
At first, the lack of this explanation doesn't prohibit the physicists to develop the water surface models of quantum mechanics. They don't care for why their models are working, they're just happy, they're working - and this formal attitude is extremely widespread in contemporary physics. The modern physicists really don't care why their theories working, until they're working. We have Maxwell theory of light, general relativity for description of gravity field - but do we have complete explanation of these models? Of course not.
Dethe
1 / 5 (1) Mar 15, 2015
At second, I'm not formally thinking physicist, so I already put the question, why the water surface analogies of space-time work so well for wide range of phenomena? IMO the answer is in ancient Boltzmann brain concept, developed at the end of 19th century. We can imagine, that the Universe is random space-time system composed of density fluctuations of every size and complexity thinkable and we are just these most complex density fluctuations in it (so-called the Boltzmann brain). How this random blob would interact with the randomness of the rest? Well, this is a geometric question, the solution of which will not depend on any interpretation anymore. But it's complex problem, so we can only estimate its main aspects in a given moment. For example we can check the symmetry of objects observed in our Universe. We are surrounded with spherical stars and large planets, but the smaller and larger objects aren't symmetrical anymore. The same repeats at the small distance scale.
saila
not rated yet Mar 15, 2015
To put this another way: The speed of light isn't just the cosmic speed limit of light. On a more fundamental level it is the cosmic speed limit of classical information transmission.
(i.e. if we ever do find a way to break that barrier then that would mean the end of Relativity).


This could be called playing with words. Two entangled electrons or photons are doing something that is happening faster than speed of light. Unless we think that they are connected, but even then, if they can be and are connected while they are on the opposite side of the universe that we can see, then there is more than the speed of light anyway.
And then what is connected to what? To what extent?
The speed of light is the maximum theoretical speed known to science, and nothing more than that. Teleportation is happening faster than that, I would like to say that its speed is faster than light, because this is what we observe, it is not a theory but the reality.

Dethe
1 / 5 (1) Mar 16, 2015
that would mean the end of Relativity
IMO not, simply because such a process doesn't belong into realm of relativity. The relativity is alive and well even during superluminal information transfer in quantum way. The relativity just prohibits us to follow the propagation of information along whole path in determinist way. But when photon or another particle tunnel through barrier, then it literally dissolves in vacuum at one side of barrier, transport itself in form of longitudinal waves of vacuum (which are superluminal) across it - and after then it reemerges at the another side of barrier. No casual motion can be observed/traced during it. Instead of it, what we actually observe is the decay of one particle and emerging of another one at another place. Such a process may indeed look suspicious for us, but the relativity has nothing to say both for both against such a process, because no macroscopic motion did actually happen during it.
Dethe
3 / 5 (2) Mar 16, 2015
We shouldn't doubt that the tunneling can be used for superluminal information transfer, because such an experiments were done already with prof. Günter Nimtz during tunneling of light across macroscopic barrier between two prisms. The light wave was modulated with sound frequency and it did cross the barrier with speed slightly higher than the speed of light, while its modulation has been preserved. But what you will lose is the information about exact position of original source of light (whole the surface of barrier emanates the evanescent waves during it) - so that the causality of special relativity has been still preserved at the local level.
antialias_physorg
not rated yet Mar 16, 2015
Two entangled electrons or photons are doing something that is happening faster than speed of light.

That's why Einstein called it "spooky ACTION at a distance", not "spooky information transmission at a distance". He chose his words very carefully.
And then what is connected to what? To what extent?

That's the real question, now, isn't it? Hidden variables? Holographic universe? We don't know.
But it's not information teleportation. All experiments that have been done to that effect (and there have bin quite a lot) seem to come out with this one constant: If you want (classical) information transmission you're limited to c.
smd
not rated yet Mar 16, 2015
@antialias_physorg: Did you read the entire article? It quotes the researcher saying exactly the opposite: "Typical teleportation can teleport an unknown quantum state perfectly by using subsequent local operations. However," Zhang points out, "in the last step of the present scheme, the sender will obtain two measurement results of the single atom state, and the recipient can obtain the teleported state perfectly only if the sender's measurement result is a Rydberg state."

The point is that the scientist who is one of the paper's authors explicitly characterizes this as entanlement-based telelportation achieved without the need for classical communications by providing "a new way to create entanglement, and so, albeit inconceivably, two qubits can be entangled without interaction." - and as everyone knows, Einstein was referring to quantum entanglement.
antialias_physorg
not rated yet Mar 16, 2015
The point is that the scientist who is one of the paper's authors explicitly characterizes this as entanlement-based telelportation

Yes.
However they explicitly state (and I quoted this in a previous comment already):
meaning that the present scheme can transport an unknown qubit in a nondeterministic manner without prior entanglement sharing or classical communication between the participants.

Note the 'unknown'. We are dealing with quantum information. Not classical information. Quantum information can teleport. Classical information cannot.

Classical information is the correlation between an a priori _known_ state and an a posteriori measured state. In quantum information you do not know the a priori state (if you set/measure it you break entanglement). Therefore it is not classical information.
Dethe
1 / 5 (1) Mar 16, 2015
Quantum information can teleport. Classical information cannot
I don't understand, how you would classify the information mediated in Nimtz experiments (or this one described above). If it can be observed and measured in classical means, then it's classical in this way or another. The difference rather is, that the teleporting is not causal deterministic motion in classical sense. It merely works like destruction of one state at some place and recreating it at another place. Whereas the quantum information cannot be cloned, neither deleted, neither teleported. IMO you're confusing subjects.
indio007
not rated yet Mar 16, 2015
First, the "speed of light" is a constant not a limit.
The commonly known speed only applies to the far field.
In the near field, the magnetic and electric forces are decoupled.
"Tunneling" phenomena propagates faster than far field light as what pointed out by another commenter in regards to Gunter's Nimtz's experiments as well as many many other experiments.

The coulomb force is provably instantaneous.

The gravitational force must be instantaneous as well or at least 50x the speed of light for the solar system orbits to remain stable i.e. there is no "retarded gravity".

antialias_physorg
not rated yet Mar 16, 2015
I don't understand, how you would classify the information mediated in Nimtz experiments (or this one described above). If it can be observed and measured in classical means

They have no a priori information. They do not know the state of the entangled entities till after the measurement. Hence this cannot be used to transmit information (if you cannot know what you encode then you cannot send a message).

What it can be used for is encryption, because encryption does not add information to a signal. In encryption you only need a correlation between two states, but not a correlation between a priori and a posteriori states (you only have two a posteriori states).

...which is actually one of the most beautiful proofs of the difference between classic information and quantum information I've come accross.

(Nimitz' measurement seems to be a measurement of group velocity - which can exceed c - but is not a demonstration of faster than c information transmission)
smd
not rated yet Mar 16, 2015
The point is that the scientist who is one of the paper's authors explicitly characterizes this as entanlement-based telelportation

Yes.
However they explicitly state (and I quoted this in a previous comment already):
meaning that the present scheme can transport an unknown qubit in a nondeterministic manner without prior entanglement sharing or classical communication between the participants.

Note the 'unknown'. We are dealing with quantum information. Not classical information. Quantum information can teleport. Classical information cannot.

Classical information is the correlation between an a priori _known_ state and an a posteriori measured state. In quantum information you do not know the a priori state (if you set/measure it you break entanglement). Therefore it is not classical information.


Yes, you did - and just as it was that time, your incorrect assertion has again been immediately refuted based on your lack of understanding.
Dethe
1 / 5 (1) Mar 16, 2015
Nimitz' measurement seems to be a measurement of group velocity - which can exceed c
Can the group velocity mediate the classical information? If yes, then the information can exceed c. I'd say yes, if we can measure it and find it superluminal. Of course, when the evanescent waves or group velocity can violate the classical causality, then we could utilize it for various negentropic and antigravity phenomena, because the violation of Lorentz symmetry implies the violation of another well established laws.
smd
not rated yet Mar 27, 2015
@Bill_Gaede wrote
Mr. Zhang would do well in learning the basics of Physics before publishing irrational explanations such as 'medium-less' entanglement. Spooky action-at-a-distance is not so spooky as it seems to the mechanics and other mathemagicians who propose to do 'physics' without mediators.

Ignoring your unnecessarily insulting comment, at least have the respect to use the appropriate honorific - i.e., Prof. Zhang.

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