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Let the electrons dance!

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#1
WEST LAFAYETTE, Ind. - A team of Purdue University researchers is among a small group in the world that has successfully created ultrapure material that captures new states of matter and could have applications in high-speed quantum computing.

Yay! Or maybe nay?

The material, gallium arsenide, is used to observe states in which electrons no longer obey the laws of single-particle physics, but instead are governed by their mutual interactions. Quantum computing is based on using the quantum mechanical behavior of electrons to create a new way to store and process information that is faster, more powerful and more efficient than classical computing. It taps into the ability of these particles to be put into a correlated state in which a change applied to one particle is instantly reflected by the others. If these processes can be controlled, they could be used to create parallel processing to perform calculations that are impossible on classical computers.
Still long way to go ...

-||-
snip

The research team designed and built equipment called a high-mobility gallium-arsenide molecular beam epitaxy system. The equipment makes ultrapure semiconductor materials with atomic-layer precision. The material is a perfectly aligned lattice of gallium and arsenic atoms that can capture electrons on a two-dimensional plane, eliminating their ability to move up and down and limiting their movement to front-to-back and side-to-side.
That's really cool. That's what they say. Let's see what's next:

At room temperature, electrons are known to behave like billiard balls on a pool table, bouncing off of the sides and off of each other, and obey the laws of classical mechanics. As the temperature is lowered, electrons calm down and become aware of the presence of neighboring electrons. A collective motion of the electrons is then possible, and this collective motion is described by the laws of quantum mechanics. The electrons do a complex dance to try to find the best arrangement for them to achieve the minimum energy level and eventually form new patterns, or ground states.
Arrrgh those nasty electrons!

"We are basically capturing the electrons within microscopic wells and forcing them to interact only with each other," he said. "The material must be very pure to accomplish this. Any impurities that made their way in would cause the electrons to scatter and ruin the fragile correlated state." The electrons also need to be cooled to extremely low temperatures - close to absolute zero ....
lolwut? I've stopped reading after that ...

http://www.purdue.edu/newsroom/research/2011/110727ManfraCsathyMBE.html
 
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twilyth

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#2
It sounds like they're talking about the Cooper pairs you have in superconducting materials. They don't actually communicate though - at least not as far as I can tell from the wiki entry. I've never read very much about the phenomenon and I've never heard of particles communicating except when entangled. Even there it's not clear that there is any actual communication - just some connection that transcends space (and possibly time - don't remember).

edit: OK, never mind, they are talking about entangled electrons - I think that's what they mean by "correlated." The problem is keeping the entangled particles from interacting with any other particles or forces since that collapses the wave function of all of the entangled electrons and eliminates them as being useful for quantum computing.
 

Solaris17

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#3
It sounds like they're talking about the Cooper pairs you have in superconducting materials. They don't actually communicate though - at least not as far as I can tell from the wiki entry. I've never read very much about the phenomenon and I've never heard of particles communicating except when entangled. Even there it's not clear that there is any actual communication - just some connection that transcends space (and possibly time - don't remember).

edit: OK, never mind, they are talking about entangled electrons - I think that's what they mean by "correlated." The problem is keeping the entangled particles from interacting with any other particles or forces since that collapses the wave function of all of the entangled electrons and eliminates them as being useful for quantum computing.
stopped reading. poster went crazy
 
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twilyth

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#4
stopped reading. poster went crazy
I am indeed a few sammichs short of a picnic, but I'm a pillar of rationality compared to quantum mechanics. That is some crazy ass shit.

New Type Of Entanglement Allows 'Teleportation in Time,' Say Physicists


Jay Olson and Timothy Ralph at the University of Queensland in Australia say they've discovered a new type of entanglement that extends, not through space, but through time.

They begin by thinking about a simplified universe consisting of one dimension of space and one of time.

It's easy to plot this universe on a plane with the x-axis corresponding to a spatial dimension and the y-axis corresponding to time.

If you imagine the present as the origin of this graph, then the future (ie the space you can reach at subluminal speeds) forms a wedge that is symmetric about the y-axis. Your past (ie the space you could have arrived from at subluminal speeds) is a mirror image of this wedge reflected in the x-axis.

When two particles are present, both sitting on the x-axis, their wedges will overlap in the future and in the past. This has a simple meaning: these particles could have interacted in the past and could do so again in the future, but only in the areas of overlap.

Conventional entanglement cuts across this world, quite literally. It acts along the the x-axis, linking particles instantly in time and in defiance of the boundaries to these wedges.

What Olson and Ralph show is that entanglement can just as easily work along the y-axis too. In other words, entanglement is so deeply enmeshed in the universe that a measurement in the past has an automatic influence on the future.

continued at link.
If anyone would like to 'splain this to us science geeks, please do. Try to use small words though. My brain hurts. :cool: :laugh:
 

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#5

Solaris17

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#7
are you teasing me? I can help but get the feeling that you are somehow amused by the fact that its a tad hard for me to grasp how electrons can just lol time. though to be honest i didnt make it past AP physics i took all the genetics courses. im sure IRL me and you could have a fine conversation.
 
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twilyth

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#8
are you teasing me? I can help but get the feeling that you are somehow amused by the fact that its a tad hard for me to grasp how electrons can just lol time. though to be honest i didnt make it past AP physics i took all the genetics courses. im sure IRL me and you could have a fine conversation.
I don't understand. I was trying to give some additional info that I thought would be helpful - helpful to me as well. I don't have a science background except for being an avid reader of things like SciAm and Science News.

I'm not trying to be a dick or anything, although I seem to have a knack for coming across that way.
 

Solaris17

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#9
I don't understand. I was trying to give some additional info that I thought would be helpful - helpful to me as well. I don't have a science background except for being an avid reader of things like SciAm and Science News.

I'm not trying to be a dick or anything, although I seem to have a knack for coming across that way.
hahaha no no i didnt mean to insinuate that you were comming across as rude. I just thought you were playing a little.
 
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twilyth

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#10
No not at all.

I put that parenthetical comment in because I've read about experiments that do seem to mess with the time line. They're all a little hazy though since a) they're not easy to understand in the first place and b) I need to see the same concept several times before it really sinks in.

Then when you mentioned that it was a crazy idea, I was anxious to give an example. Not to prove you wrong or anything but just because I think it's so fascinating and I didn't want to pass up an opportunity to share.

Honestly I had never heard of the experiment I quoted, but it seemed like a good example of entanglement ignoring time boundaries so I figured it was the perfect article to cite - even if it didn't and still doesn't make a whole lot of sense.

I'm going to try to work through the Wired article though once I can focus a little bit. I'm pretty wired from sleeping all day so my mind is all over the place right now. :)
 

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#11
No not at all.

I put that parenthetical comment in because I've read about experiments that do seem to mess with the time line. They're all a little hazy though since a) they're not easy to understand in the first place and b) I need to see the same concept several times before it really sinks in.

Then when you mentioned that it was a crazy idea, I was anxious to give an example. Not to prove you wrong or anything but just because I think it's so fascinating and I didn't want to pass up an opportunity to share.

Honestly I had never heard of the experiment I quoted, but it seemed like a good example of entanglement ignoring time boundaries so I figured it was the perfect article to cite - even if it didn't and still doesn't make a whole lot of sense.

I'm going to try to work through the Wired article though once I can focus a little bit. I'm pretty wired from sleeping all day so my mind is all over the place right now. :)
if you want a real mind boggle about time entanglement and quantum mechanics give this a quick read.

http://www.physorg.com/news198948917.html

the specific article talks about avoiding the grandfather paradox. but imagine if CTC's can be controlled without a time machine? then maybe the processors of the future wont have the migration or AB problem that was being discussed in the other thread.

EDIT:: it actually covers very briefly particle tunneling at the end.
 
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twilyth

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#12
Wow. Crazy coincidence. I actually read that article last year and it didn't mak any sense to me then either. I guess what they're trying to say is that you pre-select the states a particle would be able assume in the past so as to post-select only states that would not create a paradox. OK. That sorta makes sense but how do you pre-select a state in the present that would manifest the desired state in the past. that's where it breaks down for me and i'm just like 'damn, these guys are so far out of my league.'
 
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#13
they are talking about entangled electrons - I think that's what they mean by "correlated."
No. Correlated motion got nothing to do with entanglement. They just forced electrons to behave smarter. But somehow it's confusing. I heard that electrons ignore classic laws anyway. Like one electron can go through two holes at the same time. However it's really interesting. GaAs crystal sounds more exciting than graphene.
 
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twilyth

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#14
Hmm. I guess I'll have to read it again. Normally quantum computing involves having multiple particles in a state of superposition. Each superposed particle being a qubit. I thought that they also had to be entangled but I guess I should check.
 
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#15
You can read an abstract of article about correlated motion of electrons here:

When the onsite correlation is strong, electrons can move by usual hopping only on to empty sites but they can exchange position with their neighbors by a correlated motion.
http://www.sciencedirect.com/science/article/pii/0921453489911647

And here are links about entanglement/spookiness

Quantum entanglement gives quantum computers the ability to perform a "not" operation for free. Since the spin of two entangled electrons is fixed and opposite with respect to each electron, if one electron is set to a known spin (that is, up versus down), then the second electron must, instantly acquire the opposite spin of the first.
http://www.davidjarvis.ca/entanglement/spookiness.shtml
http://www.davidjarvis.ca/entanglement/quantum-entanglement.shtml
http://www.telegraph.co.uk/science/...n-acts-at-10000-times-the-speed-of-light.html
 

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#16
Awesome first post. :D

Yeah, see, us qubits are way way more powerful than you can ever imagine... muhahahaha! :laugh:

And we can even transend time. How's that for a party trick?
 
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twilyth

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#17
I do understand the concepts and the 2nd and 3rd links were very interesting. I'm going to bookmark that whole series. I'm especially interested because apparently entanglement depends on interaction with the zero point field - at least I read that someplace and I think that makes it even more fascinating.

Anyway, I figured that both superposition and entanglement were required for quantum computing - especially since entanglement is a special form of superposition.

The first link made no sense to me at all. Do you know how this type of correlated movement is different from Cooper pairs or is that something entirely different?
 
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#18
Cooper pairs got to do with superconductivity and BCS theory (if my memory serves me correctly) when coupled electrons can act as a boson and condense into the ground state. In my opening post article they didn't talk about this effect. They got ultra-pure GaAs crystal (it's a semiconductor just like Si or Ge) with a bunch of electrons with hyper high mobility which move in 2D space. In my opinion these two effects look different to me (tho both of them require ultra low temperatures). This subject is really wide and complex, the more research the better.

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/coop.html#c2

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
http://hyperphysics.phy-astr.gsu.edu/hbase/quacon.html#quacon
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/supcon.html#c1
 
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#19
Mmm I took my time and read that article (with a big headache I admit). So they say that if you sent a qubit in past and detect it in future then this "cause-effect" thingy can be called time entanglement (if I got that right lol *shrug*). However they didn't say a single thing about the speed of that process....

Really I dunno ... after reading all of that now I start to think that either time is space's girlfriend or time doesn't exist at all. If everything (always) moves in space then it automatically moves in time. And if speed is very high (close to speed of light) then time slows down. Hmmm so if I want to stop time for some system then I either need to completely freeze all its particles or to accelerate it to the speed of light?! Ok I digress ...

I found a really interesting book Electron Scattering and it has a chapter called Quantum Time Entanglement of Electrons:

http://www.springerlink.com/content/m275684qkr33409x/

Btw this book also talks about correlation and entanglement:

Correlation is often significant in electron scattering from atoms, nuclei and bulk matter. Mathematically, as well as conceptually, correlation and entanglement are defined in the same way. Both correlation and entanglement connote mixing.
Go figure ...
 
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#20
Scientists entangled ions using microwaves

Physicists at the National Institute of Standards and Technology (NIST) have for the first time linked the quantum properties of two separated ions (electrically charged atoms) by manipulating them with microwaves instead of the usual laser beams, suggesting it may be possible to replace an exotic room-sized quantum computing "laser park" with miniaturized, commercial microwave technology similar to that used in smart phones.
Here's their ... rig



Microwaves are the key!

Microwaves, the carrier of wireless communications, have been used in past experiments to manipulate single ions. But the NIST group is the first to position microwaves sources close enough to the ions—just 30 micrometers away—and create the conditions enabling entanglement, a quantum phenomenon expected to be crucial for transporting information and correcting errors in quantum computers. Ions are a leading candidate for use as qubits to hold information in a quantum computer. Although other promising candidates for qubits—notably superconducting circuits, or "artificial atoms"—are manipulated on chips with microwaves, ion qubits are at a more advanced stage experimentally in that more ions can be controlled with better accuracy and less loss of information.
... and entangled ions too.

Quantum computers would harness the unusual rules of quantum physics to solve certain problems—such as breaking today's most widely used data encryption codes—that are currently intractable even with supercomputers. A nearer-term goal is to design quantum simulations of important scientific problems, to explore quantum mysteries such as high-temperature superconductivity, the disappearance of electrical resistance in certain materials when sufficiently chilled.
yeah and also video encoding and gaming I suppose ....

The same NIST research group previously used ions and lasers to demonstrate many basic components and processes for a quantum computer. In the latest experiments, the NIST team used microwaves to rotate the "spins" of individual magnesium ions and entangle the spins of a pair of ions. This is a "universal" set of quantum logic operations because rotations and entanglement can be combined in sequence to perform any calculation allowed by quantum mechanics
The sooner I forget about 1s and 0s and start thinking about rotations and entaglement the better.

Well done, NIST.

http://www.nist.gov/pml/div688/microwave-quantum-081011.cfm
 
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#21
http://www.physorg.com/news/2012-01-choreographing-electrons-pursuit-quantum.html

Bump. Another interesting read:

Managing billions of spinning electrons

To achieve their results, the researchers suspended the sample of pure silicon inside a cylinder filled with liquid helium, dropping its temperature to 2 degrees Kelvin. They locked the cylinder between two doughnut-shaped rings about the size of pizza boxes that control the magnetic field around the sample and sent microwaves through the silicon, and coordinated the spins of about 100 billion electrons.

"The first pulse twists them, the second reverses them, and at some point the sample itself produces a microwave pulse, and we call that the echo," Lyon said. "By doing the second pulse, getting everything to reverse, we get the electrons into phase."

Describing the electrons' phase, or the state in which they exist, can be tricky, like a lot of things in quantum mechanics. When scientists talk about electrons, they use the term "spin." For subatomic particles such as electrons, spin is a fundamental characteristic that can make them behave like tiny magnets.


The highly purified sample of silicon-28 has a very low magnetic signature at the atomic level, and therefore does not disrupt the spin of the electrons.

Maintaining the spinning phase is what scientists call "coherence." Unlike objects in the everyday world, subatomic particles, which operate under the rules of quantum mechanics, can be in more than one place at the same time. Electrons' spin, for example, can be classified as up, down, or in superposition, a state that is both up and down simultaneously. It is this superposition state that allows for the highly complex mathematics at the heart of quantum computing.


edit: November 16, 2012

Two teams working independently have succeeded in entangling a single electron spin with a single photon in a solid-state platform.
Sounds cool

To create a quantum computer, scientists believe it will be necessary to combine or connect stationary qubits with mobile qubits. Thus, research has been focused on building a system in which this is possible. In this new research, quantum dots were used to represent the stationary particles while photons were used to represent those that fly. To connect them, the researchers relied on entanglement between pairs of particles and the properties they share.
The process is complex and tricky

In their labs, both teams used very small semiconductors to trap a single electron, e.g. a quantum dot. They then both fired a laser at the dot to set its spin state to either up or down (representing "0" or "1"). Next both teams also fired another laser pulse at the dot to force it to a higher energy level. Doing so caused an entangled photon to be released as the energy decayed. The photon was emitted as either horizontally or vertically polarized with a wavelength that was demonstrated by either a red or blue color. It was at this stage that the work between the two teams diverged. To use the information from a (qubit) in a quantum system, only one of the two properties can be allowed to exist; thus the other must be removed. The first team's work involved removing the color, the second, the polarization. To remove the color the first team ran the photon through a crystal that was also shot with a laser beam. Doing so caused the colors to smear which was enough to remove that property from the entangled particles. The second team removed the polarization by allowing the photon to pass through a polarizing filter which forced it into an anticlockwise state which effectively erased the shared property from the particles.
http://phys.org/news/2012-11-entangle-electron-photon-quantum-dot.html
 
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#22
We're one step closer to ... quantum cryptography.

Research physicists have demonstrated the first device capable of amplifying the information in a single particle of light without adding noise.
Sounds promising. Because quantum information is useful but very fragile and normal amplification techniques destroy it. The key feature of photon amplifier is that it preserves the quantum information and may help overcome the current distance limitations of quantum communication.

http://phys.org/news/2012-11-noiseless-photon-amplifier.html

This is the first time the information stored in a single photon has been amplified. The technique works by combining the noisy quantum state with a 'clean' single photon in the amplifier, and using quantum teleportation to transfer the information onto the new photon. The most obvious application for this work is in improved quantum cryptography; secret messaging which is guaranteed secure by the laws of physics.
Cool amplifier. I want one or two. Distance can eff off :D
 
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#23
Now it's not just electrons or photons. For the first time it's entire atomic ensembles!



One step closer to quantum memories.

Now for the first time, physicists have demonstrated quantum teleportation by entangling two remote macroscopic atomic ensembles, each with a radius of about 1 mm.

In the quantum teleportation experiment performed here, the two atomic ensembles each consist of about 100 million rubidium atoms and are connected by a 150 m optical fiber, but physically separated by about half a meter in the lab. The atomic ensembles act as quantum memories due to their ability to store photonic qubits within their stationary matter system. Along with quantum teleportation, quantum memories are another key component of quantum communication.
So it's collective teleportation. Sounds cool.

In experiments, the scientists demonstrated that they could teleport a collective atomic excitation (spin wave state) from one ensemble to the other. To do this, they first mapped the spin wave state of the first atomic ensemble to a propagating photon, and then performed Bell state measurements on that photon and a second photon that was already entangled with the spin wave state of the second atomic ensemble. Once the two photons were projected into an entangled Bell state, the quantum information was teleported to the second atomic ensemble.
Sounds easy but it's complicated.

http://phys.org/news/2012-11-quantum-teleportation-atomic-ensembles.html