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Researchers Control the Flip of Electron Spin
karvind writes "According to PhysOrg, physicists in Europe, California and at Ohio University now have found a way to manipulate the spin of an electron with a jolt of voltage from a battery. In this experiment voltage was applied to Indium Arsenide based quantum dot which flipped the spin of electron inside it and emitted a photon. The scientists were able to manipulate how long it would take for the electron to flip its spin and emit a photon - from one to 20 nanoseconds. This may have possible applications in optoelectronics and quantum cryptography. Results were published in the latest issue of Physics Review Letters"
Was I the only one who thought this read "Researchers Control the Flip of Election Spin"?
All universities new findings take 30 years before they are applied to the corporate world.
1.) show the slashdot how electron flips
2.) slashdot crowd say cool
3.) show more engineers
4.) show sponsors, marketers, businessmen
5.) repeat step 4 for 29 years
6.) profit!
*...voltage was applied to Indium Arsenide based quantum dot which flipped the spin of electron inside it and emitted a photon. The scientists were able to manipulate how long it would take for the electron to flip its spin and emit a photon - from one to 20 nanoseconds.*
When you put it that way, I don't know why it wasn't this simple the whole time!
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Does this development get us any closer to the development of a quantum computer? I don't even remember the last I heard about that branch of science...
I hate the one hundred and twenty character limit for signatures with an all-enveloping, all-destroying, incredible pass
fewer electrons.
The List of Grievances with Slashdot.
funny how the numbers game will go backwards by then.
The title of the linked-to article in Physical Review Letters is:
"Voltage Control of the Spin Dynamics of an Exciton in a Semiconductor Quantum Dot"
(Emphasis by be)
Now an exciton is something quite different from an electron.
The Tao of math: The numbers you can count are not the real numbers.
No, I don't think the two effects are related at all...
"A dark exciton with total angular momentum L=2 ecomes a bright exciton with L=1."
Finally a practical application for decay dynamics following nongeminate excitation
How about an ansible?
Pair off two electrons in a shell, flip the rotation of one and you change the rotation of another - instanteously. Even if they're no longer in the same atom and millions of miles apart.
The only surefire protection against Microsoft infections is abstinence. - The Onion
I found myself reading this article quite mindful of the frequency of stories recently that suggest the US is headed down a dangerous path of neglect and ignorance. Not only in the arena of biological research (stem cell, et al) but in technological developments as well. This is not a matter of observation but rather official administrative policy http://science.slashdot.org/article.pl?sid=05/04/0 2/183230&tid=98&tid=103&tid=190&tid=215&tid=231&ti d=14 .
"The study was funded by EPSRC in the United Kingdom, Ohio University, Volkswagen, and the Alexander von Humboldt Foundations, with additional support by the Scottish Executive and the Royal Society of Edinburgh"
It seems to me that this is exactly one example of the type of technology the government should be promoting, for military benefit or not. What I am not sure of is wether the researches had the option to solicit US funding or if they chose rather to not bother?
I don't know, it struck me as a little odd considering that we're told repeatedly about how important it is to be a world leader in economy, technology, and security here is something that promotes all three and the pentagon's fat couffers are nowhere to be found. (well potentially compromises the third, but that's another story)
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As I recall, there was an episode of Deep Space Nine that played with this idea about controlling an electron's spin. There was a device which would randomly make an unusual proportion of electrons spin in one direction, the the result was that a person's luck would be changed to either unusually good or unusually bad. I thought it was an intersting idea on what might happen if you change one of the fundamental aspects of matter in that spins are always balanced, some kind of quantum conservation of momentum.
Cryptography is in a desperate state right now. Virtually every product that needs to include it has in implemented in such a way that it's basically useless. And so quantum crypto is rolling in more and more these days with newer and better discoveries (like the one here) coming out periodically. However, yeah, it's great, w00t, applications for quantum crypto, etc, but that doesn't really mean much. We already have messages that are unbreakable through brute-force. All that needs improvement through our crypto is more secure ways of entering information into computers and sending it without screwing up by keeping the message in RAM, storing it in a temp file, etc.
So sure, the ability to flip the electron spin is great for quantum cryptography itself, but...how does that help anyone, really?
An explanation for this interaction taking place has been to say that the two not connected objects are actually still connected... just not connected in space but some sort of "phase-space" ...
My question now is: are they still connected afterwards! They should be, shouldn't they??
If the spin can be willyfully changed that could mean instantaneous transmission of data...
Since there is no free lunch this problably will not work... either because the entanglement is only valid for one measurement or it was never there. I wouldn't be surprised if the entanglment effect is just a theoretical construct to make modelling reality easier...
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sigamajig...
Neither did Einstein. He didn't accept parts of it, anyway, which is why he pretty much wasted the last decades of his life searching for a GUT that would never work.
No. The measurement destroys the entanglement.
The Tao of math: The numbers you can count are not the real numbers.
I don't think Einstein wasted his life on arguing against QM. If it was not him, the subtleness of QM wouldn't have been exposed. And the issue raised by him isn't resolved completely. You can refer to J Bell's paper to understand why it is not a trivial problem. Currently QM is accepted because it works and there had been various non-intutive way to explain them (hidden variables, parallel universe etc). And again if you think nothing useful came out of GUT, you are only reading popular science articles and not Phy Rev papers.
Entangled quantum things aren't connected in any way except mathematically. It's nothing more than saying that if you have two electrons entangled with opposite spin, then measuring one of them tells you the spin of the other, without you having to measure it. When you measure the spin of the first one, you've disturbed it as a result, and it no longer has any relationship to the other electron at all. However, the cool and useful thing is that you have gained information about another electron without measuring it.
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what about flipping the spin before measuring?
That may seem screwball, but doesn't simply flipping the spin effect the other entangled particle? Would it also flip? If so, would it give off any measurable signal (a photon)?
I don't care about determining the spins of the particles (and hope they stay undeterminable), I just care about making them repeatedly give of signals at selected time intervalls...
(I suppose that would mean that the spin shouldn't be determinable from the emitted photon, otherwise that would equal a measurement...)
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sigamajig...
What if the unsuspecting electron is one of a correlated pair? When the flip occurs, does the sibling electron (perhaps a galaxy away) simultaneously flip
No. Flipping the spin is performing a measurement.
In addition, gravity is not related to particle spin and magnetism. Oh, well, at least not any more than we already knew, that gravity is a bastard among forces that wrecks just about any perfectly good unifying theory in one way or another.
Now, let me walk out onto the "imagine things and make physicists laugh at you" plank (especially before I RTFA) -- I've wondered a little, in the NMR case, if it would be possible to induce nuclear fission or at least some kind of nuclear decay through heavy RF excitation of nuclei. It seems slightly reasonable that the added energy would make crossing the barrier between temporary stability and decay a little lower. Now, why you would prefer this over bombarding the stuff with neutrons, well, that's another matter...
By "Pair off two electrons", I presume you mean put them in an entangled state where the spins of the two electrons are correlated? (For example, in the state |up, down> + |down, up>).
In that case, your system won't work. Putting one of the electroncs in this spin-flipping device would destroy the fragile entanglement. In other words, flipping the spin of one would do nothing to the other.
This is how it always is with entanglement -- entangled particles only remain entangled as long as you leave their entangled properties alone. Once you measure or modify the properties of one, the entanglement is ruined.
There's no reason for a sig here.
what about flipping the spin before measuring?
Flipping the spin is measuring in the quantum mechanical sense. Perhaps you should think 'interaction' instead of 'measurement'.
Spin is angular momentum. Angular momentum is conserved. Thus, to change the angular momentum of something means interacting with it.
I don't care about determining the spins of the particles
It doesn't matter if you care or not. It doesn't matter if you look at the results or not. It doesn't matter if it's you even have a result. What matters is that an interaction happened, where you could, in theory have received information about the spin state.
absolutely riveting.
What you're saying is that the spin is already determined and *not* yet undetermined? I've never quite known what to think about that. I would, as you suggest, also prefer the theoretical construct notion. But it seems this is not yet clear...?
The author of the Wiki page actually begs to differ:http://en.wikipedia.org/wiki/Quantum_entang lement
and implies that the entangled particles do
interact :
Although two entangled systems can interact across large spatial separations,______________________________________________
sigamajig...
What you said it mostly correct. However, it is theoretically possible (and has been done in practice as well, in fact) to flip a spin without performing a measurment. Flipping a spin is not always a measurment.
If you start in the state (normalization constants ignored):
2 * |up, down> + |down, up>
where the first electron is more likely to be measured in the up state, and you apply a "coherent spin flip" (ie a flip performed WITHOUT measuring the spin) to the first electon, you end up in the state
2 * |down, down> + |up, up>
This is still an entangled state, and the spin of each electron is still indeterminate. Contrary to the desires of the parent to your comment, however, you still have not managed to flip the spin of the second electron.
There's no reason for a sig here.
are they still connected afterwards! They should be, shouldn't they??
I think they are. I also think you make me think of Homeopathy and stuff like that. Interesting!
I hope I didn't brain my damage.
I suppose that would mean that the spin shouldn't be determinable from the emitted photon, otherwise that would equal a measurement...
I understand that the manipulation doesn't get to lead to a way of deducing the spin. Of course "cares" don't influence reality, it was a figure of speach. cool down.
I was assuming that the manipulation would not equal a meassurement, and it seems there are ways to do so as the my "neighbour-poster" explained.
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sigamajig...
or does it mean the spin of the particle has not been (for lack of a better word) "set" yet?
The Wiki authors aren't clear about it: http://en.wikipedia.org/wiki/Quantum_entanglement
Saying one thing: Although two entangled systems can interact across large spatial separations, ... ... no useful information can be transmitted in this way,
and then another:
If the particles are interacting then information is being transmitted. To say that it's not usefull is more of a copout. It is just maybe not yet possible for us to meassure some kind information while keeping the particles in an indeterminate state (e.g. without meassuring the spin state).
(Of course what Wiki authors write has no bearing on reality, it could be that the spin states are set, which is also the simplest explanation.)
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sigamajig...
An army physicist I worked with as an undergrad used entagled photon polarization as a method to make remote measurements. Because particular compounds can specifically polarize light, polarization of one photon will cause the immediate polarization of its entangled sister photon. (This means that you could, in theory, shine a laser beam at a chemical vapor a mile away, and by reading the polarization states of trapped entagled photons, remotely measure the vapor's composition)
The facinating thing is that this "information" transferral happens instantly. A polarization change in one photon immediately results in the polarization of its sister, regardless of the distance between them.
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http://slashdot.org/comments.pl?sid=151085&cid=126 72458
As a simple analog it can be compared to multplying an unknown number with -1. It flips the sign but it doesn't set the sign or determine the value.
So the grandparents question remains open... what is "entanglement"? This isn't a new question/dilemma, Einstein didn't like it and called it "spooky action".
It boils down to the question what is an "indeterminate state"?
does it mean the particle has a spin that simply has not been meassured yet?
or does it mean the spin of the particle has not been (for lack of a better word) "set" yet?
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sigamajig...
I have always been boggled how "indeterminate state" was to be understood.
If it meant the particle has a state that simply has not been meassured yet?
Or if it meant the state of the particle has not been (for lack of a better word) "set" yet?
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sigamajig...
Perhaps you don't realize that you've made an extremely controversial statement. What you claim this army physicist did is contrary to accepted quantum mechanics since circa 1930. Do you have any evidence to back up this claim?
According to quantum mechanics, the interaction of the "remote photon" can not produce a measurable change on the "local photon" in the way you have described.
There's no reason for a sig here.
The great Richard Fenyman said that "anyone who was NOT confused by and annoyed at quantum mechanics did not understand it"!
"Everyone is entitled to their own opinion, but not their own facts."
Isn't this the beginning steps towards the interstellar travel mechanism used in the James Blish series "Cities in Flight"? at amazon which was affectionately nicknamed the "spindizzy"?
The excited scientists set up a new experiment to show this, but were perplexed when they started getting photons flying out of the test chamber.
Curiously they formed a pattern:
ALL U BASES ARE BELONG TO US! W00T!
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Information wants to be free.
Sure, so do Tibetans, but information called dibs.
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Somebody needs to be taken out back and shot! ;-)
At least not with static magnetic fields realizable on earth - you might be able to get some interesting stuff happening with magnetar level fields.
OTOH, there is some interesting stuff that happens with nuclear quadrupole moments and gamma ray emissions. The gamma ray emissions show some directionality when the thermal energy drops below the quadrupole resonance energy. This effect is used to calibrate microkelvin thermometers.
A Shadeless room is a brighter room.
These appear to be the same type of quantum dots used to create artificial atoms.
Artificial atoms, as I understand it anyway, are exhibited when these wells/quantum dots are crafted to store electrons in certain configurations (modeling "orbital shells"/energy levels?). The quantum dot has then been shown to exhibit some properties of an element corresponding to that electron configuration.
Is there a connection somewhere here with the electron spin "flip" (whatever that means)? If you take an ordinary atom and add energy, the electrons jump/change to higher energy levels and when returning to a lower state emit the excess energy as a photon. This seems strangely coincidental.
I'm not a physicist and maybe I'm out of touch with current terminology/models of subatomics so don't be too harsh if my explanations seem naive.
On another note, I wonder if it's possible to model the unstable elements (112-118 and beyond) using this quantum dot approach. What fascinating properties might be exploited that would otherwise be impossible to tap due to their nearly instant decay.
...storage?
6 66.htm
If you can flip the spin of an electron, wouldn't that be a condensing of our current storage technology?
However, after doing a Google for the size of an electron as compared to an atom, this road bump chucked my question out the window.
http://www.newton.dep.anl.gov/askasci/phy00/phy00
I know that you were probably joking, but this more thorough explanation explains how a photon could be emitted when the electron's spin flipped without violating the law of conservation of energy. How does it explain this? I have no idea.
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http://www.zamandayolculuk.com/cetinbal/teleport ation2.htm
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Call me back when they finally get the transporter working, so they can BEAM ME UP!!
This is a quantum teleportation experiement. Reading from the link:
"Also, quantum teleportation does not allow for faster-than-light communication. Although the teleported particle attains the polarization value instantly, the people at the sending station must convey the fact that teleportation was successful by making a phone call or using some other light speed or sub-light-speed means of communication."
This statement, from the link you quote, contradicts your implication that quantum entanglement can be used to transmit classical information faster than the speed of light. Perhaps you did not mean to imply that in your post. At the time, given the other posts to this story in that vein, that's how I read your comment.
Aside from that, I don't see how this teleporation scheme can be used, in your words, to "shine a laser beam at a chemical vapor a mile away, and by reading the polarization states of trapped entagled photons, remotely measure the vapor's composition". Which photon is the one that passes through the vapor, photon M? If so, then a detector is needed at the site of the vapor, along with a beamsplitter and a second detector as described in the link, along with communication equipment to "phone home" when teleportations are successful.
There's no reason for a sig here.
I lost the reference in editing. It's the Wikipedia article on giant magnetoresistance
Any sufficiently advanced libertarian utopia is indistinguishable from government.
But that's not flipping a spin. It's flipping two spins, which is different because the total angular momentum is the same before and after the flipping.
Teleportation only works in this scheme 25% of the time. It would not be sufficient to say "I'm done on this end", you would need to specify which teleportation attempts were successful. Thus, you need one classical bit for each teleported quantum bit.
There's no reason for a sig here.
you're right, it's a scam; one that even works on animals, though. I'm so glad that there's nothing physics couldn't explain - and every inexplicable thing therefore cannot exist at all.
I hope I didn't brain my damage.
My notation was |spin of first electrion, spin of second electron>.
Initially, I was in a superposition of |up, down> and |down, up>.
Then, I performed an operation that flips the spin of only the first electron, leaving me in state |down, down> + |up, up>
I have not flipped two spins. And what does angular momentum conservation have to do with it? In this case, the expectation value of total angular momentum is conserved, but there's no need for that to be true in general of a unitary operation.
There's no reason for a sig here.
Initially, I was in a superposition of |up, down> and |down, up>.
Ok. I don't understand this. I don't think that's not a eigenfunction of the spin-projection of a pure spin state.
Can you explain how this coherent spin-flip works in more detail?
|up, down> + |down, up> is not an eigenstate of the spin flip operator. Correct.
However, that doesn't mean you can't apply the spin-flip operator to it. I don't know how to explain it in more detail, other than to try and give an experimental realization, which I don't think is what you're looking for.
Perhaps this will make more sense... let's work in "vector notation"...
define |up, up> = (1, 0, 0, 0)
|up, down> = (0, 1, 0, 0)
|down, up> = (0, 0, 1, 0)
|down, down> = (0, 0, 0, 1)
The spin flip operator for the first electron can now be written in matrix form as
0 0 1 0
0 0 0 1
1 0 0 0
0 1 0 0
Since this matrix is unitary (see http://mathworld.wolfram.com/UnitaryMatrix.html), then this is a valid time-evolution operator in quantum mechanics.
I guess I really haven't said anything new here, so I doubt that actually clarifies anything. But I'm not sure what it is you don't understand.
There's no reason for a sig here.
Ok, got it.
I made the mistake of assuming you were talking about stationary states.