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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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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.
"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.
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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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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?
Not exactly I am afraid. There are still huge issues to quantum computing. Namely isolation and data retrieval.
A quantum computer (or at least it's processor) needs to be totally shielded to the outside world while it operates as any interraction or mesurement from the outside world will break the theory. Also, at this moment, you cannot retrieve the processed data without interfering, right? So as soon as you get the data from one of the virtual processors working in 'other worlds', the thing breaks and you can't get anything anymore from it. So it's in fact pretty useless I'm afraid.
I don't think we're going to see a quantum computer in the years to come, and much less under our desks. Even if they were invented I believe our governments will keep them away from us as they could be quite mean to encryption.
This advance deals with manipulating the spin of a single electron (a single qubit) The hard part of quantum computing is reliably maniuplating two qubits. With single qubit operations and measurements, and a two qubit CNOT, one can perform arbitrary quantum computation.
Quantum error correction can be used to fix quantum errors. If the errors are independent, local, then there is a fault tolerant threshold, below which you will be able to correct enough errors to do arbitrary quantum computation. Error correction will typically add polylog (polynomial in log n) overhead in the number of qubits and the running time. So Shor's factoring algorithm becomes O(n^3 log^a n) instead of O(n^3).
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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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.
No, it doesn't need to be completely sheilded. As far as 'reading' the information simultaneously detroying the quantum state, that is true...just like reading a memory cell that uses a capacitor destroys the information, yet we miraculously still build computers with them :P. Also, the application of quantum computers is quite limited (factoring numbers is one thing they can do well), don't expect to be playing Doom 6 on them.
And don't think of that 'other world' explanation. It's not really what is happening according to current theory, just a convenient/spooky way to explain it to some lay people. And yes, IAAP
It means the spin does not yet have a determined value. And this can indeed be checked. There are probability inequalities (the so-called Bell inequalities, named after Bell who found them) which must hold if the result of measurement should be pre-determined for each particle. The laws of quantum mechanics violate those inequalities, and experiments by Aspect have shown that nature obeys quantum mechanics also in this respect (the violation of the Bell inequalities has been measured).
If those measured correlations mean interaction between those systems or not depends on which interpretation of quantum mechanics you prefer. Since there are interpretations where you don't need such an interaction, it's clear that you cannot use it to instantaneously transmit information with this effect (otherwise such interpretations couldn't possibly exist).
The Tao of math: The numbers you can count are not the real numbers.