Long-Distance Teleportation Between Two Atoms: First between atoms 1 meter apart

Jan 22, 2009
Panel 1 shows the experimental setup. Credit: JQI/UMD

(PhysOrg.com) -- For the first time, scientists have successfully teleported information between two separate atoms in unconnected enclosures a meter apart - a significant milestone in the global quest for practical quantum information processing.

Teleportation may be nature's most mysterious form of transport: Quantum information, such as the spin of a particle or the polarization of a photon, is transferred from one place to another, without traveling through any physical medium. It has previously been achieved between photons over very large distances, between photons and ensembles of atoms, and between two nearby atoms through the intermediary action of a third. None of those, however, provides a feasible means of holding and managing quantum information over long distances.

Panel 2 shows preparation of the ions. Credit: JQI/UMD

Now a team from the Joint Quantum Institute (JQI) at the University of Maryland (UMD) and the University of Michigan has succeeded in teleporting a quantum state directly from one atom to another over a substantial distance. That capability is necessary for workable quantum information systems because they will require memory storage at both the sending and receiving ends of the transmission.

In the Jan. 23 issue of the journal Science, the scientists report that, by using their protocol, atom-to-atom teleported information can be recovered with perfect accuracy about 90% of the time - and that figure can be improved.

"Our system has the potential to form the basis for a large-scale 'quantum repeater' that can network quantum memories over vast distances," says group leader Christopher Monroe of JQI and UMD. "Moreover, our methods can be used in conjunction with quantum bit operations to create a key component needed for quantum computation." A quantum computer could perform certain tasks, such as encryption-related calculations and searches of giant databases, considerably faster than conventional machines. The effort to devise a working model is a matter of intense interest worldwide.

Panel 3 show interference of photons. Credit: JQI/UMD

Teleportation works because of a remarkable quantum phenomenon, called "entanglement," which only occurs on the atomic and subatomic scale. Once two objects are put in an entangled state, their properties are inextricably entwined. Although those properties are inherently unknowable until a measurement is made, measuring either one of the objects instantly determines the characteristics of the other, no matter how far apart they are.

The JQI team set out to entangle the quantum states of two individual ytterbium ions so that information embodied in the condition of one could be teleported to the other. Each ion was isolated in a separate high-vacuum trap, suspended in an invisible cage of electromagnetic fields and surrounded by metal electrodes. [See illustrations.] The researchers identified two readily discernible ground (lowest energy) states of the ions that would serve as the alternative "bit" values of an atomic quantum bit, or qubit.

Conventional electronic bits (short for binary digits), such as those in a personal computer, are always in one of two states: off or on, 0 or 1, high or low voltage, etc. Quantum bits, however, can be in some combination, called a "superposition," of both states at the same time, like a coin that is simultaneously heads and tails - until a measurement is made. It is this phenomenon that gives quantum computation its extraordinary power.

At the start of the experimental process, each ion (designated A and B) is initialized in a given ground state. Then ion A is irradiated with a specially tailored microwave burst from one of its cage electrodes, placing the ion in some desired superposition of the two qubit states - in effect writing into memory the information to be teleported.

Panel 4 shows teleportation. Credit: JQI/UMD

Immediately thereafter, both ions are excited by a picosecond (one trillionth of a second) laser pulse. The pulse duration is so short that each ion emits only a single photon as it sheds the energy gained from the laser pulse and falls back to one or the other of the two qubit ground states. Depending on which one it falls into, each ion emits a photon whose color (designated red and blue) is perfectly correlated with the two atomic qubit states. It is this entanglement between each atomic qubit and its photon that will eventually allow the atoms themselves to become entangled.

The emitted photons are captured by lenses, routed to separate strands of fiber-optic cable, and carried into opposite sides of a 50-50 beamsplitter where it is equally probable for either photon to pass straight through the splitter or to be reflected. On either side of the beamsplitter output are detectors that can record the arrival of a single photon.

Before reaching the beamsplitter, each photon is in a superposition of states. After encountering the beamsplitter, four color combinations are possible: blue-blue, red-red, blue-red and red-blue. In nearly all of those variations, the photons cancel each other out on one side and both end up in the same detector on the other side. But there is one - and only one - combination in which both detectors will record a photon at exactly the same time.

In that case, however, it is physically impossible to tell which ion produced which photon because it cannot be known whether the photon arriving at a detector passed through the beamsplitter or was reflected by it.

Thanks to the peculiar laws of quantum mechanics, that inherent uncertainty projects the ions into an entangled state. That is, each ion is in a correlated superposition of the two possible qubit states. The simultaneous detection of photons at the detectors does not occur often, so the laser stimulus and photon emission process has to be repeated many thousands of times per second. But when a photon appears in each detector, it is an unambiguous signature of entanglement between the ions.

When an entangled condition is identified, the scientists immediately take a measurement of ion A. The act of measurement forces it out of superposition and into a definite condition: one of the two qubit states. But because ion A's state is irreversibly tied to ion B's, the measurement of A also forces B into a complementary state. Depending on which state ion A is found in, the researchers now know precisely what kind of microwave pulse to apply to ion B in order to recover the exact information that had originally been stored in ion A. Doing so results in the accurate teleportation of the information.

What distinguishes this outcome as teleportation, rather than any other form of communication, is that no information pertaining to the original memory actually passes between ion A and ion B. Instead, the information disappears when ion A is measured and reappears when the microwave pulse is applied to ion B.

"One particularly attractive aspect of our method is that it combines the unique advantages of both photons and atoms," says Monroe. "Photons are ideal for transferring information fast over long distances, whereas atoms offer a valuable medium for long-lived quantum memory. The combination represents an attractive architecture for a 'quantum repeater,' that would allow quantum information to be communicated over much larger distances than can be done with just photons. Also, the teleportation of quantum information in this way could form the basis of a new type of quantum internet that could outperform any conventional type of classical network for certain tasks."

Provided by University of Maryland

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User comments : 18

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theophys
4.2 / 5 (6) Jan 22, 2009
AWESOMENESS! It's things like this that make me love physics.
rrrn
1 / 5 (1) Jan 23, 2009
"... without traveling through any physical medium ...": false, because we do not know the future of physics. Is the vacuum empty?
gmurphy
5 / 5 (1) Jan 23, 2009
I'm glad they provided detailed diagrams describing this process, they should always be provided for complex processes like this. One thing that puzzles me is that there is no real communication between the ions. They use the correlation of photon output to deduce when the ions are in complementary states, I don't see what's so special about that?, if I'm missing something I'd appreciate enlightenment from more informed perspectives ;-)
RolfRomeo
3 / 5 (2) Jan 23, 2009
I'm merely a layman, but it seems to me that some of the information that "disappears" is retained in the researchers mind, who has to physically walk over to ion B and use what she knows of ion A to get the desired result from the experiment.

Now, not to say that entanglement isn't a neat effect, and maybe I'm misunderstanding something, but I'm really not sold on the whole teleportation thing...
Tokyo
2 / 5 (1) Jan 23, 2009
RolfRomeo,

Your intuition is correct. There article says that "What distinguishes this outcome as teleportation, rather than any other form of communication, is that no information pertaining to the original memory actually passes between ion A and ion B. Instead, the information disappears when ion A is measured and reappears when the microwave pulse is applied to ion B."

But that's not really how it works. See:
http://xxx.lanl.g.../9906007

This paper shows that all information in quantum systems is, notwithstanding Bell's theorem, localised. Measuring or otherwise interacting with a quantum system S has no effect on distant systems from which S is dynamically isolated, even if they are entangled with S. Using the Heisenberg picture to analyse quantum information processing makes this locality explicit, and reveals that under some circumstances (in particular, in Einstein-Podolski-Rosen experiments and in quantum teleportation) quantum information is transmitted through classical(i.e. decoherent) information channels.

ComplexQM
1 / 5 (1) Jan 24, 2009
Long Distance Teleportation Between Two Atoms > Not So

Well there is a bright side to this. It seems the challenge I threw out over the original claim for QM Teleportation has been taken up.
I have to take my hat off to the authors of this paper for trying.
I do not want too be unkind. It is a serious effort.
However my challenge was to create teleportation FREE of the influence of any apparatus.
From what I can see the apparatus pre-defines the paths of both ions.
In Panel 1 the experimental setup does not agree with the diagram for step one. Perhaps the purple ions in the experimental setup are meant to be light blue? I will take it that this is a simple illustrative hiccup.
I do not see how the bursts can be similar if one contains information while the other does not. Both ions seem to be subject to a picosecond laser pulse but end up with different wavelengths. I can see no immediate evidence of teleportation as both ions follow given trajectories. Where is the distance that either of these ions jump?
In fact when both beams interact (I assume they do not pass without touching) the resulting change in amplitudes for both beams can be expected so that both beams end up with different amplitudes not quantum information.

In Panel 2 there is a 50% chance of collision (or non-teleportation apparently). The results are also random. This would be upsetting if you were trying to teleport a man to Venus and his head ended up at Mercury. The whole idea of a successful teleportation would be to apply a means of reading the information without knowing what it is beforehand. Like previous experiments it appears that we can read the information IF we already know what it is! This is like having received a telegram and sending the same information. There would be no point. Worse still according to the experiment we cannot predict that the telegram will arrive at all (the beam splitter interference).
A nice attempt but I am sorry to say that I still require proof of long range teleportation outside of experimental apparatus interfering with the results. I suggest what I believe is an impossible task but if you still cling to the Uncertainty Principle you may like to try this. Remove the uncertainty at the delivery stage of any teleportation. Any such system is clearly of no practical use for teleportation if you do not know what is going to be the result with 100% accuracy: and this is crucial to success.
Please accept my apology if I am over critical.
Yours sincerely,
Alex Ross
smiffy
5 / 5 (1) Jan 24, 2009
If you accept that the researchers have managed to quantum entangle two atoms then in principle at least they have demonstrated that the quantum repeater station is possible. Ordinary photonics can be used to communicate between the stations. In theory at least vast quantities of data can be communicated through ordinary photonics between quantum computers. That definitely represents progress.

Whether you consider quantum computing to be to data processing what nuclear fusion is to energy - fantastic returns in theory but hobbled by practical considerations - is another question.

What gets me about this research is that they are claiming to entangle two atoms retroactively i.e. the independent atoms are entangled some time after the independent photons have already left. This seems to be bizarre even by QM standards. Obviously I need to do some more reading.
Noumenon
2.3 / 5 (3) Jan 24, 2009
No, the photon's to the detector are only to verify entanglement as it doesn't happen every time, once verified then the info can be extracted from the other ion.

See David Mermin for an explanation of entanglement - it's not as simple as say if one is a 'head' well then obviously the other must be a 'tail'.
MichaelJM
not rated yet Jan 25, 2009
I'm probably not understanding something, but while this is really neat, I don't see how this could be performed conceivably over large distances. Right now they have achieved a distance of a meter. It is one meter because that is the distance of the picosecond laser pulse. Does the laser pulse have to be emitted by the same device for this to be accurate? If so, that would mean that both ions would have to be connected through one laser pulse. Can this distance of a meter be conceivably lengthened then over large distances? (I just don't know)

Then both of the ions seem to be connected by this beamsplitter. It seems that both photons must pass through the same beamsplitter. How could this be achieved if the ions that emitted the photons are far apart? (Again, I just don't know)

If I'm understanding this correctly, once entanglement is confirmed, a measurement is take from ion A, and due to entanglement, the scientists will know exactly what microwave pulse to fire at ion B, in order to 'extract' the information that was in ion A. That's pretty neat, but is the hope of achieving this over long distances even in the realm of possibility, as it seems like these ions are connected (not physically) in various ways? Can anyone explain this? I'm sure I'm just not understanding something.
Thanks!
Noumenon
2.3 / 5 (3) Jan 25, 2009
I think your right Michael but not because of the distance issues with the setup. Quantum entanglement cannot be used to send USABLE messages faster than light. Although a non-local instantaneous 'influence' does occur between ion A and ion B, no matter the distance between them, it is of a useless form, in a superposition of two states. The result of ion A measurement still has to be communicated the old fastioned light speed way to where ion B is to be made use of. If someone could enlighten further, that would be great.
Noumenon
1 / 5 (2) Jan 25, 2009
.... (Penrose 1989; Ghirardi, Rimini, Weber 1980)
javjav
1 / 5 (1) Jan 25, 2009
It could be used for FTL communication.

What is tele-transported here is the "information" that is printed by the microwave pulse. But what kind of "information" are they talking about? Is it a recognizable wave pattern or is it just a Qbit?

If it is be a wave pattern (as it is drawn in the picture), then it could be easily used for faster than light communication (it would be a bit complex if it is a qbit), as follows:

- First, we build many of that teleportation machines between A and B. They will be used at the same time (in parallell) in order to save probability errors.

- Let's suppose that the scientist at B is continously applying the manipulation burst that corresponds to the situation: ion-A = "Red". He must do it at predefined times, and using many of these machines at the same time.

- When the scientist at point A wants to send a classic "1" to B, he will simply apply the microwave pattern to all teleportation machines at the same time in order to achieve a reasonable probability of success (in average, the wave pattern will only appear at B half of the times that the ions where entangled). When A trigger the laser, half of the entangled ions at A will be measured as Red, and the "information" will appear at some ions at B.

In this way B will be able to discrimate between "0" (The expected information does not appear in any machine) and "1" (some of the teleportation machines report the expected information).

If both the beam-splitter and photo-receptors are located at half the distance between the two ions, then the scientist at B can read the classical bits that are sent by A in half of the time, in comparison with a classical communication at the speed of light.

If the "information" is just a QBit and not a recognizable wave pattern, then a lot more of simultaneous teleporting machines would be necessary, but it could still work based on continous probability study, in a similar way of Bell inequality experiments.
smiffy
not rated yet Jan 25, 2009
the photon's to the detector are only to verify entanglement as it doesn't happen every time, once verified then the info can be extracted from the other ion.

If that's the case then do you know how the two ions are entangled in the first place? By what mechanism? The article is not at all clear on this. Are they entangled as a result of a pair of entangled photons from the initiating laser pulse?
Can this distance of a meter be conceivably lengthened then over large distances?

In theory over any distance. But the two stations have to be connected by fibre optics for both the laser pulse and the photon detection. The degradation of signal in a fibre optic is what will limit the distance apart (I think!). But maybe the frequency that the entanglement occurs is dependent on distance; the article is very vague on this aspect.
holoman
1 / 5 (1) Jan 25, 2009
Nothing NEW Here.

In fact the nanotechnology and all the concepts were
shall we say LIFTED from Colossal Storage entangled particle communication published and patented in 1998
MichaelJM
not rated yet Jan 25, 2009
The result of ion A measurement still has to be communicated the old fastioned light speed way to where ion B is to be made use of. If someone could enlighten further, that would be great.

@Noumenon- Yes I thought about that too. The only thing that this technology could soon result in is possibly a more secure way of sending information, as I assume the microwave pulse information is useless unless you have the other entangled ion. So this is a big step towards something useful to be sure. Teleportation? Probably, not so much.

@smiffy- Thanks, didn't realize fiber optics could be used; the article is very vague on this aspect, which is unfortunate.
Star_Gazer
not rated yet Jan 25, 2009
Beam me up Scotty!
GlenM
not rated yet Jan 26, 2009
I appears that the Universe is ridgidly homeostatic.
Adriab
not rated yet Jan 27, 2009
I like how physorg is including more diagrams into their articles.