Quantum teleportation achieved over record distances

http://www.nature.com/news/quantum-teleportation-achieved-over-record-distances-1.11163

by ananyob • 14 years ago

49 40 14 years ago

zrgiu_• 14 years ago

I know this is a long long time away but .. Could this be used to communicate faster with stuff like the Curiosity rover ? I mean, once it becomes easier to reproduce without big laboratories to actually read the quantum state of the photons.

darkstalker• 14 years ago

And although part of the transfer happens instantaneously, the steps required to read out the teleported quantum state ensure that no information can be communicated faster than the speed of light.

Seems not.

pavel_lishin• 14 years ago

It might increase bandwidth, though.

stordoff• 14 years ago

My understanding is that current quantum teleportation methods need a classical channel to transmit information (and so is limited to the speed of light). See the Protocol section of Wikipedia - https://en.wikipedia.org/wiki/Quantum_teleportation . To my knowledge, there is no particular reason to believe that this limitation can be removed.

The simplest way to see this is to consider a state such as a|0> + b|1>, which is the quantum state of the particle we wish to teleport from Alice to Bob. If Alice does the measurements needed to teleport it, Bob might end up with either a|0> + b|1> or a|0> - b|1> (or two other similar states) with equal probability.

To actually get the correct state we began with, which is the only way to transmit something meaningful, then he needs the results of Alice's measurements to make a correction. These can only be transmitted at the speed of light, so speed of information transfer is still limited to the speed of light.

RockofStrength7• 14 years ago

This phenomenon is explained by many-worlds: The two photons have both polarization orientations in the multiverse. We are limited to a single instance of the multiverse, and any interaction whatsoever between the photons and our universe will force them into a single instance of polarization orientation, as this is all we can experience, being interacting beings ourselves.

Reality is really an immense interconnected binary tree, and we must always travel along a single path. It has the property that reconciling paths (paths that diverged but met up again with no interaction in our universe) will again be accessible to us.

As Galileo was prosecuted for supporting Copernicus' heliocentric theory (more specifically for championing reason over faith), the Church's default stance was that the planets moved around the sky 'as if' they orbited the Sun. We are in a similar position now with many-worlds vs. 'as if' many-worlds, based on experimental evidence such as the Mach-Zehnder interferometer results.

enko• 14 years ago

Are you saying that a Mach-Zehnder Interferometer is a multiverse-spanning device? So shining a few lights around some polarising mirrors and putting some shit in the way is breaking inter-universal barriers? And this experiment too?

I won't pretend to fully understand quantum entanglement but jumping straight to the balls-out Infinite Multiverse Theory is a bit much. Occam's Razor, please.

Heliocentrism is and was obviously right, minus the blinders of religion. I don't think the situation re. many-worlds is even remotely comparable. Then again, if you have some compelling, credible yet accessible literature setting out the case to the contrary, why not share?

RockofStrength7• 14 years ago

"Heliocentrism is and was obviously right, minus the blinders of religion."

It is easy for us to judge now that we have pictures from space, but the concept would have been very non-intuitive in centuries past. For example, one does not feel the movement of the Earth.

"I don't think the situation re. many-worlds is even remotely comparable."

I agree that the comparison is not exact, yet it seems to be the best one available to support my stance. Both geocentrism and wave collapse were theories that appealed to commonsense notions but ignored irrefutable evidence. Geocentrists invented the preposterous epicycles, which supposedly allowed the planets to move "as if" they were orbiting the Sun. Single worlders invented wave collapse to allow photons to operate "as if" all possible paths were taken.

As far as literature goes, I'd recommend the two books by David Deutsch. He gets extremely ambitious at times, but I would classify the writing as "compelling, credible yet accessible literature".

_urga5• 14 years ago

Regarding: "As Galileo was prosecuted for supporting Copernicus' heliocentric theory (more specifically for championing reason over faith)"

Nothing could be further from the truth. The first proponents of the scientific method saw the process of describing the known universe as possible only because of their faith in a rational Creator, their definition of the word "faith" meaning "conviction backed by reason" (Hebrews 11). Their hypothesis was that the creation of such a rational Creator would necessarily be ordered, not chaotic as the pagans of the day believed, and that it would be possible to seek to describe the creation in terms of scientific laws and principles. By faith they understood that what is seen was not made out of what was visible. This was the basis for the birth of the scientific method.

In the days of Galileo, the Church as you refer to, was nothing more than a political militant state, opposed to the theology of the early Christians of the 1st century, and opposed to the Scriptures which exposed its hegemony. Indeed the Church would have mothers and fathers burnt at the stake for teaching children the ten commandments and the Lord's prayer. People like William Tyndale, and many other brilliant Oxford and Cambridge scholars were hounded and martyred by the Church for translating the Bible into English and circulating and discussing it in the 1500s.

While the Church may have opposed heliocentrism, Galileo defended heliocentrism, and understood correctly that it was not contrary to the Scriptures.

For people like Galileo and Kepler, faith and reason were the same thing. By definition, it's impossible to have faith that is not based on reason, nor is it possible to hold reason without faith. To do so is historical revisionism. If you have a bone to pick with faith, then the best place to start is with the life and death and resurrection of Christ in history. Did it happen? How soon after the events were the eye witness accounts recorded? At what cost? Independent? Do we read them as they were written? This is a matter of historicity: did it happen? Not of philosophical possibility (naturalism), or statistical possibility (frequentism).

RockofStrength7• 14 years ago

"While the Church may have opposed heliocentrism, Galileo defended heliocentrism, and understood correctly that it was not contrary to the Scriptures."

Biblical references Psalm 93:1, 96:10, and 1 Chronicles 16:30 include text stating that "the world is firmly established, it cannot be moved." In the same manner, Psalm 104:5 says, "the Lord set the earth on its foundations; it can never be moved." Further, Ecclesiastes 1:5 states that "And the sun rises and sets and returns to its place" etc. Certainly for the Biblical literalist there are places of direct disagreement.

"For people like Galileo and Kepler, faith and reason were the same thing."

I suppose one could have 'faith in reason' (that's a great oxymoron), and one could also perhaps 'reason in faith'. But at a deeper level, the two concepts are orthogonal and irreconcilable.

"By definition, it's impossible to have faith that is not based on reason, nor is it possible to hold reason without faith."

faith - Strong belief in God or in the doctrines of a religion, based on spiritual apprehension rather than proof. reason - The power of comprehending, inferring, or thinking especially in orderly rational ways.

Here is the "Galileo affair" Wikipedia link for those who wish to read up on the matter: http://en.wikipedia.org/wiki/Galileo_affair

calebmpeterson2• 14 years ago

Can you recommend any good literature discussing Galileo and Kepler and their "faith and reason" view of the cosmos? I do not ask contentiously but with genuine curiosity. In the (post) modern era there seems to be much noise about faith (Christianity in particular) and science being irreconcilable.

What little I do know about many founders of the major fields of science seems to indicate that the founding men and women saw no such dichotomy. Or at the least were willing to struggle with the questions rather than throw the entire matter out as "unscientific."

Lord Kelvin and Michael Faraday seem to have both Christians and creationists. Newton was a Christian and claimed that "all my discoveries have been made in answer to prayer." Joule (the unit's namesake) was at least a theist. Then we have Louis Pasteur, Christopher Columbus, George Washington Carver, Samuel Morse, and Blaise Pascal - each "men of faith."

Not that the above list should be taken as an argument by authority for faith. Certainly not. However, it does leave me wondering how these great thinkers saw the world so differently.

Symmetry4• 14 years ago

Of course the phenomenon is explained by Many Worlds, that's an interpretation of QM that should be consistent with the evidence we have in all cases if it's not to be discarded. Many Worlds is also hardly a persecuted viewpoint, it may not have penetrated into the popular consciousness but I seem to recall evidence that most actual physicists don't use a collapse postulate. I certainly know that my of my physicist friends here in the MIT community everyone holds with some sort of non-collapse interpretation.

EDIT: Wait, I just remembered one dual physics/philosophy major who believes in quantum collapse. But even she thinks that the Copenhagen Interpretation, the one you usually see in the media, is ridiculous.

I'll say that, personally, I find it much easier to make sense of situations involving long range entanglements when I think about them in terms of Many Worlds than when I think about them in terms of waveform collapse. And the term "teleportation" as applied to these results really does annoy me.

RockofStrength7• 14 years ago

Thank you - it is nice to get feedback from someone in the community. I agree that Many Worlds is not literally persecuted, but it is viewed as something of an absurdity by the layman, and seems to be a bit taboo among the elders in the field. The preference of a public panel is often to throw up one's hands at the mystery of it all, which encourages people like Deepak Chopra to muse on the magic of consciousness' power to collapse the wave function.

derleth• 14 years ago

> As Galileo was prosecuted for supporting Copernicus' heliocentric theory (more specifically for championing reason over faith)

Aside from the fact this is factually incorrect, it's also a bad argument, as most people who propose paradigm-shifting theories are wrong.

Using this argument associates you with a lot of crackpots a lot more strongly than it associates you with Galileo.

RockofStrength7• 14 years ago

"Aside from the fact this is factually incorrect..."

I shall supply a snippet of the Galileo affair that corroborates my hand-wavy statement:

"One of the first suggestions of heresy that Galileo had to deal with came in 1613 from a professor of philosophy (what we would now call a professor of scientific theory), Cosimo Boscaglia, who was neither a theologian nor a priest. In conversation with Galileo's patron, Cosimo II de' Medici, Boscaglia gave the opinion that the telescopic discoveries were valid, but the motion of the Earth was obviously contrary to Scripture." http://en.wikipedia.org/wiki/Galileo_affair#Bible_argument

"...most people who propose paradigm-shifting theories are wrong."

Galileo's success worked against him - other paradigm-shifters were not legitimate threats to the status quo.

jacoblyles• 14 years ago

Lame.

Many worlds is an interpretation. It is an untestable explanation of the evidence, there is no way to decide between many worlds and other models (besides, perhaps, convenience). It is not physics, but metaphysics.

I know some people are pushing many worlds with religious fervor and it is obnoxious. But as far as I know, despite the horde of internet acolytes that gives MW a weird thought-smell, it is still a mainstream interpretation and nobody is "prosecuted" for it.

RockofStrength7• 14 years ago

"Many worlds is an interpretation. It is an untestable explanation of the evidence, there is no way to decide between many worlds and other models (besides, perhaps, convenience)."

Many Worlds is the theory that best fits the evidence of quantum experiments, keeping in mind Occam's razor. In fact, it is the only comprehensible one. Wave collapse is comparable to epicycles in that they are both attempts at harmonizing completely contradictory evidence with a preconceived common-sense assumption (single universe and geocentrism, respectively).

Mitt• 14 years ago

Often “why”-questions are interpreted as criticism. I would like to ask one, just because I am curious: why are people interested in this for communication? With current technology we can communicate with within the limits of the speed of light. We can also encrypt communication. So, what makes this technology so interesting, that people may want to use it in the future? Will it be cheaper? Faster? More secure/better encrypted?

thomaslangston• 14 years ago

From the article:

Teleportation can also securely transmit quantum information even when Alice does not know where Bob is. Bob can take his entangled particle wherever he pleases, and Alice can broadcast her instructions for how to ungarble the teleported state over whatever conventional channels — radio waves, the Internet — she pleases. That information would be useless to an eavesdropper without an entangled link to Alice.

JeremyBanks• 14 years ago

As far as I can tell, this just seems like an obscenely overcomplicated one time pad. Instead of Alice giving Bob a string of bits that are known in advance, she gives Bob an entangled particle that can be collapsed to determine a string of bits at a later date. I can't see any security benefit.

This is very neat from a purely scientific perspective. It seems pointless and misleading to try to present it as having direct practical value.

sukuriant• 14 years ago

So a VERY advanced version of this could be used for things like:

* underground/underwater communication systems where wires and radio waves faulter

* interstellar communication without antennae and without bouncing the signal off satellites

* radiowave-less espionage

* etc?

tbrownaw• 14 years ago

It allows sending quantum information over a classical channel, at 2 bits per qbit.

Of course you have to have already prepared and sent the same amount of qbits... maybe sending qbits "as needed" is harder than sending them in bulk in advance?

mootothemax• 14 years ago

With current technology we can communicate with within the limits of the speed of light.

Despite knowing close to nothing about this field, I'd hope that error-correction code would be somewhat simpler, resulting in less padding and more data going through. Think about the problems with dial-up telephones alone, lots of noisy lines and so you have to pad the data with enough error detection that it's still recoverable at the other end of the line.

It's been nearly two decades since I last studied this, but something about parity check matrices is screaming away in my head. Could be very wrong about that though.

jaekwon• 14 years ago

If you can't retrieve the information "quantum teleported" until something else bridges the gap afterwards, then how can you say that anything was teleported at all?

There would have to be a qualitative or quantitative difference between what was supposedly teleported and the "key" that must be transfered afterwards. Either you can teleport a gigabyte of information and retrieve it with a kilobyte key, or you can teleport a material thing with a "key" comprised of less information needed to encode its molecular structure.

Otherwise, teleportation seems to be a misnomer.

srl• 14 years ago

> Otherwise, teleportation seems to be a misnomer.

It is. People call it teleportation because when you attempt to mesh the results you get from experiments involving quantum entanglement with our intuitive model of physics, it looks like something has been teleported instantaneously (the state of the photon or what have you). But in reality, no information is transmitted faster than the speed of light, and there's no good reason that will change.

greeneggs• 14 years ago

People call it teleportation because it moves the state of a system from one place to another, without going through the intermediate positions. I'm not sure where this idea came from that teleportation has to be "instantaneous." From special relativity, we know that the word "instantaneous" isn't even well-defined, except in a fixed reference frame.

Basically, quantum teleportation takes the quantum state of a system, measures it. The measurement destroys the system and converts it into classical information that can be sent over a phone line. The information, once received, can be used to reconstruct the initial state.

If you think of a classical system, as computer scientists usually do, this is not very surprising. It seems obvious that in principle you could look very carefully at a complicated classical system, a human being for example, write down all of its details down to the positions of the individual atoms as a long classical string, and send this information down a phone line to reconstruct the person at the other end. It is only surprising because quantum teleportation works with quantum systems, and we know that there is no physical way of extracting all the details of a quantum system as a long classical string (Heisenberg's uncertainty principle, etc.).

sp3322• 14 years ago

The point is that you can exactly recreate a particle including its entire quantum wave function (preserving uncertainties) from one place to another without "existing" in between. That's why it counts as teleportation: you get the same object, not a similar object but the same object all they way down to quantum fluctuations, at a distance.

Symmetry4• 14 years ago

That actually isn't how this works. Yes, you do have two objects with entangled wavefunctions but that isn't remarkable at all. And the entanglement occurs when the objects are created at the same place, and then they proceed to the measurement points using entirely conventional slower-than-light means.

Its only a single bit, the polarization of the photon, that is found to have been determined in both places simultaneously. Its true that this is a new piece of information that arises in both locations simultaneously, but since this is a thing that appears in two places rather than something that moves from place A to place B I'd argue that the term "teleportation" is pretty misleading here. After the measurement the measured particle is hopelessly entangled with the measurement apparatus and through that with the surrounding universe, so the unique link between the two particle is hopelessly broken at that point.

Quantum teleportation achieved over record distances

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