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One piece closer to a working electronic quantum computer puzzle kit.

Many believe the next generation of supercomputers will be powered by quantum mechanics. Harnessing the strange properties of photons and electrons in special states is often the backbone for quantum computer research. Some of these seemingly exotic properties have already been demonstrated using photons, but until very recently, were not replicated in solid-state systems by electrons.

A group of European researchers, consisting of institutions from France, Spain and Germany, has published their work with quantum entanglement using electron (Cooper) pairs, quantum dots and carbon nanotubes. Quantum entanglement is a quantum state of matter where two particles, typically photons or electrons, form a matched pair based on their physical qualities such as up or down spin for electrons and polarization for photons. When a pair of these particles becomes entangled, quantum mechanics states that measuring one of the pair will instantly force the unmeasured into a corresponding state, regardless of the distance they have been separated by.

In photonics work, researchers used wave guides and polarization filters to form entangled photons, which can then be separated by a beam splitter and measured individually. But for electrons, the work is far more taxing. Measurements are more easily skewed by background noise and leakage from the components of the test device.

The solid-state device used to confirm electron quantum entanglement is fairly simple in design. A superconducting element is used to form Cooper pairs. The pairs then move down the element towards a carbon nanotube. Occasionally the pair is split by the nanotube and each electron moves towards a separate quantum dot. In this time, one electron’s spin can be measured, which infers the spin of its mate instantaneously. These pairs can either be spin-correlated or anti-spin-correlated (spinning in the same direction or opposite directions), but the measurement of one always reveals the properties of the other.

Quantum entanglement could be very useful in theory, especially for quantum computing in the areas of security and data transmission. Theoretically, data can be transferred over any distance instantly and without any risk of security breech, however, the entangled pair still has to be transferred through physical media at this time.



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By 91TTZ on 1/13/2010 9:28:10 AM , Rating: 0
That's not the way I took that. I took it as meaning that once entangled and split, the members of the pair will always have the same properties. It's not that you changed them instantaneously, it's that they're identical and one reveals the state of the other.

I don't think it would enable instant communication since no information is being transferred from one of the pair to the next once they're split. Their properties just happen to be identical and measuring one tells you what the other is.


By SciTech on 1/13/2010 9:37:08 AM , Rating: 1
Actually, once one partical of the pair is read and its state determined, the other paired partical instantly "chooses" a state regardless of its position in the universe. That change could be considered faster than light although information is not necessarily exchanged fast than light. Through inference we can communicate faster than light though. There have been tests on the speed at which entangled particle "choose" states once one is measured. Its thousands if not millions of times faster than the speed of light. Possibly completely instant. http://blogs.discovermagazine.com/80beats/2008/08/... a study trying to determine the speed was published in Nature.


By 91TTZ on 1/13/2010 10:32:51 AM , Rating: 2
From reading the article on Wikipedia, it seems that my belief was correct.

Measuring one of the pair does not "choose" the other. Once entangled, the other already exists in an identical (or exact opposite) state. It looks like once entangled, the members of the pair *always* have the same (or direct opposite) properties, it's not like there's any information being transferred from one of the pair to the other. You can't choose the state of one of the particles, you merely observe it, and the other member of that pair will always have identical properties.

Let me use the following example. We'll consider particles to be boxes. We'll choose any 2 boxes, labeled Box 1 and Box 2. Inside those boxes will be a letter from the alphabet. In non-entanglement, each box will have a random letter, so if you choose any 2 boxes they'll most likely have different letters (according to the probability of having any given letter).

You observe Box 1: B
You observe Box 2: R

You observe Box 1: Q
You observe Box 2: D

Now we deal with entangled boxes.

You observe Box 1: U
You observe Box 2: U

You observe Box 1: G
You observe Box 2: G

One might believe that by observing the letter in Box 1, you're instantaneously determining which letter is in Box 2. But that wouldn't be correct. In actuality, both boxes already had the same letter in them once they became entangled, and regardless of where or when you observe the two boxes you'll find that they have the same letter in them.


By Mitch101 on 1/13/2010 10:42:39 AM , Rating: 2
91TTZ: I have a radical idea. The door swings both ways, we could reverse the particle flow through the gate.
Dr. Peter Venkman: How?
91TTZ: [hesitates] We'll cross the streams.
Dr. Peter Venkman: 'Scuse me 91TTZ? You said crossing the streams was bad!
91TTZ: Cross the streams...
Dr. Peter Venkman: You're gonna endanger us, you're gonna endanger our client - the nice lady, who paid us in advance, before she became a dog...
91TTZ: Not necessarily. There's definitely a *very slim* chance we'll survive.
[pause while they consider this]
Dr. Peter Venkman: [slaps Ray] I love this plan! I'm excited to be a part of it! LET'S DO IT!


By MrBlastman on 1/13/2010 12:36:32 PM , Rating: 2
Brings a new meaning to the phrase "the old ball and chain."

What did the newly paired electron say to its mate?

"Hey babe, you make my head spin," the electron said to the other electron as she played on the round-a-bout.

It's true folks, even at the subatomic level it has been proven that female electrons tend to discombobulate a perfectly normal, sane male electron once they tie the knot.


By Akrovah on 1/13/2010 11:49:35 AM , Rating: 2
Yes, but if you can, say, FORCE your box 1 to be G, then through the entanglement wouldn't box 2 then also change to a G? I'm not a pyhisist so I don't know if that holds, but its seems to be implied if they are talking about using this for computing and such.

If that holds true, the you can easily designate one state as 0, the other as 1, and then you have instant binary communication.


By GourdFreeMan on 1/13/2010 12:30:29 PM , Rating: 2
No, in his analogy if you force your box to change its letter (state) it is no longer entangled with the other box. Free energy in the environment will eventually break entanglement as well (unless you exist in a perfect vacuum at absolute zero with no other particles that can influence your entangled pair). Notice how they are having difficulty keeping the electrons entangled in the article? Its easier to keep photons entangled because they don't interact with EM fields or other photons (as far as we know from existing experiments).


By GourdFreeMan on 1/13/2010 12:34:03 PM , Rating: 2
Grammarians note: replace "its" with "it's" in my post.


RE: Does this means instant communication is possible?
By rs1 on 1/14/2010 4:02:35 AM , Rating: 2
Are you sure about that? I thought entanglement implied a stronger relationship between the particles than just "their state is the same until something modifies one of them". If it does use the weaker definition, then I don't see why the concept is considered so important, as it can't possibly be that hard to generate two particles in the same initial state, and then they could be said to be "entangled" until someone modified the state of one or the other. Hell, I could perform entanglement on the macroscopic scale under that definition by just placing two different baseballs on the table. They would be "entangled" until I moved one of them to somewhere else.

As I've understood it, entanglement implies that the state of the particles is not only synchronous, but that it will also automatically be maintained as such when modifications are made to one particle or the other. If that isn't the case, then what is so special about entanglement anyways?


By AnnihilatorX on 1/14/2010 9:54:14 AM , Rating: 2
It can be easily think of in layman ways by anyone as follows:

Imagine a pair of photons generated by positron-electron annihilation, the pair of photons will fly in opposite direction with exact opposite spin property (up on photon 1 and down on photon 2). Of course you don't know which way photon 1 is pointing before you measure it, and any arbitary direction can be an 'up'. So you have to determine the spin and vector of photon 1 by observing it. When you observed the spin of photon 1, knowing that it is say spining up, you immediately know photon 2 must be spinning the opposite vector (down). That's basically entanglement. Photon 1 and 2 are entangled because of their anti-spin correlation.

Quote from Wikipedia:
quote:
Measuring one member of the pair therefore tells you what spin the other member would have if it were also measured. The distance between the two particles is irrelevant.


This does not allow any information to be transmitted, as the properties exists in advance.

Quote from Wikipedia:
quote:
If each particle departs the scene of its "entangled creation" with properties that would unambiguously determine the value of the quality to be subsequently measured, then the postulated instantaneous transmission of information across space and time would not be required to account for the result of both particles having the same value for that quality.


By foolsgambit11 on 1/13/2010 1:33:21 PM , Rating: 2
You're forgetting that, in quantum physics, until measured, the particles are considered to exist in both states, and neither. What you've described seems to be local realism - i.e., that the state already existed, and then we just measured it. Unfortunately, experiments have all but disproved that this is the case. I can't say that I understand it all myself, but that's why I trust a competent authority to let me know the scientific consensus. Anyway, look up "Bell test experiments" on Wikipedia, and know that when they're talking about local hidden variable theories, they're talking about theories that try to preserve local realism, as you described it.

In other words, I'm pretty sure that tens of thousands of particle physicists haven't been engaging in one big thought experiment - "ooh, what if particles weren't definite until we looked, and before that, they were everything! and nothing!" - for the past 80 years without justification. There actually is experimental evidence that particles don't have a specific state until measured.


By GourdFreeMan on 1/13/2010 3:32:51 PM , Rating: 2
http://en.wikipedia.org/wiki/Superdeterminism

False premises lead to false conclusions.

You would be surprised how enduring erroneous beliefs are when they are essentially philosophical rather than matters of scientific practicality.


By foolsgambit11 on 1/14/2010 12:05:46 AM , Rating: 2
Yes, that is always a possibility, I suppose. And it can't be ruled out any more than an omnipresent, omnipotent, omniscient god can be. The point, though, is that from a scientific standpoint, the theory that has the most predictive power given our current level of knowledge is the one I described above. To conflate a predictive theory with a philosophical argument simply muddies the issue.

I would love for quantum mechanics to suddenly become clear and somewhat-more-sensible, like our understanding of electromagnetism did, progressing from philosophical constructs about the aether, with all of its relatively arbitrary properties, to the elegant (if slightly mind-bending) theory of special relativity. But the theoretical construct (the 'why', so to speak) isn't really the point. The math is; the facts are. Special relativity doesn't explain the 'why' either. It does explain and predict the who, what, when, and where, though. That is the point of science. Scientific theories must have predictive power. Quantum mechanics has it, while superdeterminism is useless - it's just throwing our hands up in the air.


By SlyNine on 1/14/2010 5:23:32 AM , Rating: 2
We are not talking about beliefs, we are talking about theories that can be tested and potentially disproved.

So far the tests show the theories to be accurate, so if you are attacking the theory then you're the one that needs to consider using valid premises and offering a conclusion.


By wookie1 on 1/13/2010 10:56:02 AM , Rating: 2
But the Heisenberg Uncertainty Principle came from the problem that the act of measuring quantum particles or whatever affects the particle. Would this then affect the coupled particle elsewhere in the universe? This is fascinating stuff!


By AnnihilatorX on 1/14/2010 5:52:32 PM , Rating: 2
quote:
Heisenberg Uncertainty Principle came from the problem that the act of measuring quantum particles or whatever affects the particle.


No, the Heisenberg Uncertainty Principle comes from the absolute theoretical limit that momentum and position is coupled, as wikipedia puts it: Position and momentum cannot both be known to arbitrary precision. That is, the more precisely one property is known, the less precisely the other can be known.

The entanglement however, is the entanglement of intrinsic physical property of particles, not extrinsic property like speed and position. Entangled particles do not exist in the same space of course, that's not what entanglement is about, nor it is momentum.


By Jacerie on 1/13/2010 11:28:22 AM , Rating: 2
Communication with entangled particles is quite possible, but it involves other technology beyond the entangled particle. This base concept of quantum communication relies on a device with the ability to alter the spin of an entangled particle on demand to recreate the effect in it's paired particle. This would in essence give us the ability to send bits of data through the spin change that the device containing the 2nd particle could read and transmit. It's best to think of entangled particles as a binary switch in this instance. Left spin = 1, right spin = 0. With the particles being entangle, distance no longer becomes a factor as long as one of the devices is physically transported to it's destination.

This would still be the interstellar variant of Morse code, but if multiple particles could be manipulated with one device a feasible communication system could be possible to the degree we see today with our wired networks.


By Torment on 1/13/2010 12:40:48 PM , Rating: 2
Except that is simply not possible. Sorry, no (meaningful) action-at-a-distance.


By GourdFreeMan on 1/13/2010 1:47:50 PM , Rating: 2
Even if you were to construct a chamber that mirrored the effect on the other particle, the communication would still take place at speeds no faster than the speed of light, however. Suppose the photons you use to influence the particles are emitted on your end of the chamber, it will take at least d/c for the second particle in the pair to be influenced (where d is the distance between particles, and c is the speed of light). Suppose the photons are released from the middle of the chamber. Both particles will be influenced at some time at or later than d/2c (relative to a stationary observer at the center of the chamber), however it will also take at least d/2c for you to communicate to the center of the chamber to release the photons. If the target measures his particle before d/c, there will not have been adequate time for your forceful change to have propagated to his particle. The particles are only entangled before either has been acted on, and have a relationship (which can't technically be called entanglement if their state if known) after both have been acted upon (presuming neither has been disturbed while you have been waiting all this time for the communication to take place).

If your chamber only influences the entangled particles as they travel without breaking their entanglement (e.g. without forcing them into a known state), then you aren't communicating anything, as you don't know what state the particles will be in when you measure them until you do. At best you are both getting the results the chamber is designed to force upon the probabilities of the particles being in a given state.

Entanglement is primarily a statement about the observer's knowledge (which influences probabilities), not about the action of forces.


By Spuke on 1/13/2010 2:10:41 PM , Rating: 2
If we knew the entangled states, could we use those states as a "data"? For example, if you have a stream of entangled particles whose states were known, could you parse out the desired particles to form a known string of particles to be used as data?


By Torment on 1/13/2010 4:32:29 PM , Rating: 3
NO, NO, NO, NO.

They are entangled *because* they the quantum wave function has not collapsed (which corresponds to collapsing to a state). Say, for example, that an atom emits two electrons simultaneously such that the net spin must be zero. Both electrons are in a superposition of quantum wave states of up and down. When you measure electron1's spin state, you force a collapse of the quantum wave state, thus forcing electron1 to be either up or down. Since the net spin must be zero, this forces electron2 to be the opposite spin--instantaneously, no matter the distance. However, since the spin measurement on electron1 is entirely probabilistic, so is the resulting spin state on electron2. In fact, anyone observing electron2 would not be able to determine if its wave state had been collapsed by its counterpart having already been observed (otherwise, you could still transmit information).

IOW, everything looks completely random at both ends.


By Torment on 1/13/2010 4:38:38 PM , Rating: 2
Beware the errant 'they'


By Spuke on 1/13/2010 4:41:32 PM , Rating: 2
quote:
IOW, everything looks completely random at both ends.
Are they in completely random states only or can they be stateless also before observation? Or is that the same thing? Thanks for the explanations.


By Fritzr on 1/13/2010 8:59:34 PM , Rating: 2
In the case of unknown until observation, stateless and random but identical to partner give identical results when observed. If stateless the wave form collapses to one value or the other and that value is observed. Random, the particles have an unknown value until observed and that value is observed. It will require some test of the pre-observation state to distinguish the difference.


By Torment on 1/14/2010 6:38:08 PM , Rating: 2
Your entire post is rather incoherent and nonsensical, but I just want you to think about your last sentence. Do you see the logical fallacy?


By Fritzr on 1/15/2010 5:52:43 PM , Rating: 2
Yep. I did not add a big arrow saying this was a fallacy due to my belief that it is obvious to a reader paying attention.

To clear up the other.
1) If the particles are stateless until caused to collapse by observation, then a discrete value is observed.
2) if the values have a random, but discrete value prior to observation, then a discrete value is observed.

The observed value in case 1 is indistinguishable from the observed value in case 2.

The logical fallacy of the final statement implies that a different test is required to determine if the particles are stateless or possessing a definite state that has a discrete value.

Observation of the discrete value says nothing about the state of the particle before observing it's value.


By Torment on 1/13/2010 8:57:16 PM , Rating: 2
An important distinction is that the electron is not both both up and down at the same. Rather, their wave function is in some admixture of states corresponding to up or down. The electron isn't spin up or spin down until you observe it, the act of which collapses the wave function. This is a probabilistic event, meaning that if the wave functions were in an equal admixture, it's a coin toss whether the electron ends up as spin up or spin down.

So, if I understand your question, the electrons, prior to observation, have no (spin) state. It only has wave functions corresponding to physical states. In the example given, those wave functions have equal probabilities, so that when you observe a stream of electron1's, it will have a random distribution of spin-up and spin-down. Because they are entangled, observing electron1 will force electron2 into opposing state, but to the observer of electron2, it is still purely random, even though it is deterministic at this point.

If, however, you could measure whether a wave-state had been collapsed *prior* to your observing it(and you were careful about timing, as doing so is surely an act of observation and you want observer1 to observe first), observer1 could then send signals in the form of stream segments that were either observed or unobserved on his end. Unfortunately, that is not knowable, so still no action at a distance.


By GourdFreeMan on 1/13/2010 4:36:06 PM , Rating: 2
For Quantum Computing I think they are more interested in using the probabilities to do useful computation, rather than knowing the states themselves.

I'm not sure if that answers your question...


By Spuke on 1/13/2010 4:47:59 PM , Rating: 2
quote:
I'm not sure if that answers your question...
It does in a way. It makes my question irrelevant when it comes to Quantum Computing. :) I don't know much (pretty obvious) about this subject but it's really fascinating.


By Torment on 1/13/2010 4:35:26 PM , Rating: 2
This is just gibberish.


By Fritzr on 1/13/2010 8:53:15 PM , Rating: 2
Not commenting on feasibility or ability here, but IF it was possible to modify an entangled pair repeatedly, setting value with one and reading the other, then it would not be Morse Code, but a quantum serial port.


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