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Researchers Develop New Way to Generate Superluminal Pulses

May 14 2012 at 2:03 PM
Stanley16 

 





First Light:
Researchers Develop New Way
to Generate Superluminal Pulses




[linked image]




Researchers at the National Institute of Standards and Technology (NIST) have developed a novel way of producing light pulses that are "superluminal" -- in some sense they travel faster than the speed of light. The technique, called four-wave mixing, reshapes parts of light pulses and advances them ahead of where they would have been had they been left to travel unaltered through a vacuum. The new method could be used to improve the timing of communications signals and to investigate the propagation of quantum correlations.

According to Einstein's special theory of relativity, light traveling in a vacuum is the universal speed limit. No information can travel faster than light.

But there's kind of a loophole. A short burst of light arrives as a sort of (usually) symmetric curve like a bell curve in statistics. The leading edge of that curve can't exceed the speed of light, but the main hump, the peak of the pulse, can be skewed forward or backward, arriving sooner or later than it normally would.

Recent experiments have generated "uninformed" faster-than-light pulses by amplifying the leading edge of the pulse and attenuating, or cutting off, the back end. The method introduces a great deal of noise with no great increase in the apparent speed. Four-wave mixing produces cleaner, less noisy pulses with a greater increase in speed by "re-phasing" or rearranging the light waves that make up the pulse.

In four-wave mixing, researchers send 200-nanosecond-long "seed" pulses of laser light into a heated cell containing atomic rubidium vapor along with a separate "pump" beam at a different frequency from the seed pulses. The vapor amplifies the seed pulse and shifts its peak forward so that it becomes superluminal. At the same time, photons from the inserted beams interact with the vapor to generate a second pulse, called the "conjugate" because of its mathematical relationship to the seed. Its peak, too, can travel faster or slower depending on how the laser is tuned and the conditions inside the laser.

In the experiment, the pulses' peaks arrived 50 nanoseconds faster than light traveling through a vacuum.

One immediate application that the group would like to explore for this system is quantum discord. Quantum discord mathematically defines the quantum information shared between two correlated systems -- in this case, the seed and conjugate pulses. By performing measurements of quantum discord between fast beams and reference beams, the group hopes to determine how useful this fast light could be for the transmission and processing of quantum information:


ScienceDaily (May 3, 2012)





 
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AAF

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 17 2012, 12:24 AM 






Good riddance! happy.gif

This work by Stenner et al is now demonstrated by NIST to be wrong:
http://www.nature.com/nature/links/031016/031016-5.html
And the speed of information can be greater than c for pulses traveling in a medium where the group velocity exceeds c.

And therefore, the distinction between the so-called 'phase velocity & group velocity' is shown experimentally to be useless and false.















 
 
Anonymous

Confusing is easier and sells better than analysis.

May 17 2012, 5:56 AM 

"And therefore, the distinction between the so-called 'phase velocity & group velocity' is shown experimentally to be useless and false. "

The distinction between group and phase velocity cannot be false.
This results from the fact dw/dk is distinct from w/k.
The distinction cannot be useless experimentally either, since it is widely used.

However, the group velocity is only a small part of the picture.
The group velocity is not more than the first term in a series expansion.
Therefore, obviously the dispersion of a short square pulse cannot be discussed only on the basis of the group velocity. Even more so, in a nononlinear amplifying medium.

Obviously the science journalists from sciencedaily can't sell their stuff by developping a sound analysis of this experiment.
Confusing is easier and sells better than analysis.
These are real zombies, and share their bed with Pentcho Valev.

So AAF, explain how you will transmit information with this system?
Did people from NIST claim that?

For a better information, I suggest you to bypass the journalists, as well as any other a..holes like Pentcho Valev or anon.
Have a read at this paper (or at the final refereed paper if you can buy it):

http://arxiv.org/pdf/1204.0810v1.pdf

I would also suggest you to try to understand the very last sentense of this paper:

"... In particular, one can hope to use the quantum correlations to examine experimentally which part of the input pulse is causally linked to the peak of the output pulse."


 
 
Anonymous

Say good riddance to your misunderstanding.

May 17 2012, 6:40 AM 

You could also try to explain this, AAF, specially wht I have put in bold:

"There has been substantial recent interest in modifying
the group velocity of optical pulses, resulting in slow,
stopped, and superluminal light [1]. Experiments have
resulted in extremely slow light with very small group velocities
[28], while others exhibit the ability to store and
retrieve optical pulses [912]. It is also possible to generate
a dispersion relation that results in negative group
velocities [1325]. In such cases when the group velocity
of light in a material is negative, the exiting pulses
peak can appear to exit the medium before the peak of
the input pulse enters.
"

Would you also say "good riddance to causality"?

I think there is a loophole in your undersatnding of this experiment.
Don't let you influence by a..holes like Pentcho Valev and anon or journalists in general.
Try to figure out why you were too fast in saying "good riddance".
Say good riddance to your misunderstanding.

 
 
Anonymous

Stanley16,

May 17 2012, 7:06 AM 

Why do you contribute to the confusion?
Why do you think there is only Pentcho Valev the zombie that would read your post?
Why do confuse AAF, a nice guy that doesn't deserve such misleading information?
Why do you repeat these stupid journalists from ScienceDaily?
Why don't you go to the first-hand information?

I hope you did not enjoy your bad job.

 
 
Anonymous

journalists need not be as stupid as Pentcho Valev

May 17 2012, 9:07 AM 

Well, journalists need not be as stupid as Pentcho Valev.

The words "Einstein" and "Relativity" do not appear in the original paper.
http://arxiv.org/pdf/1204.0810v1.pdf
The journalists are obviously using these words to sell (or to spice) their paper.
http://www.sciencedaily.com/releases/2012/05/120503194223.htm
After all, even the original paper plays it borderline (see the title)!

Superluminal sells very well.

Does that mean that they believe this experiment means "good riddance" for "Einstein" and "Relativity" and "groups velocity"?
For sure not at all.
This sentense below from their article is not very clear.
Yet, it suggests they understand that relativity is not at stake:

"Recent experiments have generated "uninformed" faster-than-light pulses by amplifying the leading edge of the pulse and attenuating, or cutting off, the back end. "

That' why they are talking about "uninformed" FTL pulses!
Don't expect them, however, to educate their readers.
Don't expect them to think and analyse further.
They sell the paper first with a few selling words, and then they merely paraphrase the abstract.

Easy job, but useless.


 
 
AAF

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 19 2012, 4:21 PM 







"The distinction between group and phase velocity cannot be false.
This results from the fact dw/dk is distinct from w/k. The distinction cannot be useless
experimentally either, since it is widely used."



Well, Anonym; you can say that, and I won't object very much! happy.gif


However, the whole PURPOSE of resurrecting Sommerfeld's old idea
{http://www.bibsonomy.org/bibtex/259bde9d1dbe57ce257be37252eb6bfcd/vch }
about the distinction between group & phase velocities, nowadays, is to place
an Einsteinian ultimate speed limit on the transmission of information while
at the same time accepting superluminality of light waves as an experimental fact.

The fore-mentioned NIST experiment disposes with that distinction as a means
to achieve that absolute limit.

And therefore, this old idea is useless, as far as the above purpose is concerned.






[linked image]









 
 
Anonymous

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 20 2012, 3:04 AM 

AAF,

The link you provided does not work.

I don't understand what you are talking about.
You are invoking a purpose just as if it was a kind of conspiracy.
That's just irrelevant.

What do you want to prove?
What your purpose?
And are you only able to prove it by invoking a conspiracy you named "purpose".
If you can, it must not be in the field of physics.
But I even don't see you point!

I can only guess that you are in need of some challenge.
Maybe you have chosen to challenge the popular statement that "nothing could go FTL"?
If this is your challenge, then it is a poor one. (no risk and no reward)

I would suggest you a better challenge:

- try to explain the original paper better than SciendeDaily
- try to discuss if a signal can be sent FTL on this basis

In addition, you could try to analyse the history of the FTL discussions.
And after all, what does it really mean that "information cannot go FTL?".
What is the meaning of the word "signal"?

 
 
anon

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 20 2012, 7:53 AM 

>>What is the meaning of the word "signal"?


the result of Einsteinian doubletalk is to lose meaning of words, since you are an adovocate it is no wonder that you don't know what the words mean

 
 
Anonymous

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 20 2012, 10:21 AM 

As a tenant of Intelligent Design, anon should also believe that the vocabulary was intelligently created by an absilute god. So the meaning of words never changes and never needs any refinement.

anon uses the bible for everything: from a simple dictionary to a TV set manual including a full course of physics.

These bible readers are assholes.

 
 
Anonymous

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 20 2012, 11:04 AM 

AAF:
"This work by Stenner et al is now demonstrated by NIST to be wrong:
http://www.nature.com/nature/links/031016/031016-5.html
And the speed of information can be greater than c for pulses traveling in a medium where the group velocity exceeds c. "

--------------------------------

1) The work of Stenner does not contradict the paper you reference.
2) No information has been shown to propagate FTL.

What remains then from your post?
It remains that this is a quite interresting topic.

What strikes the most me is the simplicity and generality of the initial concept,
and the difficulty to analyse some experimental situations.

FTL information, causality and SR are incompatible: this is very simple.
Could the four-wave mixing process break the speed limit: that's much more subtile.
Just read the last sentense of the original paper.
http://arxiv.org/pdf/1204.0810v1.pdf .

Experimentally: it is difficult to show any FLT communication.
Stenner & all are considering a quantum correlation experiment, not to show FTL communication, but 'simply' to indenfify the correlation between emitter and receiver signals. In itself it proves that no FTL communication has been proven by Stenner. It also suggests, from the writing style that they do not expect any FTL communcation to be proven.

Theoretically: I think it is also difficult to analyse this experiment.
My personal approach would be to try a full ab-initio simulation.
This is no easy.
This is not even classical physics, quantum mechanics is involved as well as maybe a bit of statistical physics.

This paper does not deal with ab-initio simulation, but gives a feeling of what the development may look like:

http://puhep1.princeton.edu/~mcdonald/examples/negativegroupvelocity.pdf



 
 
anon

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 20 2012, 2:17 PM 

>>These bible readers are assholes.

that's still better than what you are

 
 
Anonymous

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 20 2012, 4:48 PM 


 
 
AAF

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 21 2012, 12:05 AM 











AAF: Good riddance! happy.gif This work by Stenner et al is now demonstrated by NIST to be wrong: http://www.nature.com/nature/links/031016/031016-5.html And the speed of information can be greater than c for pulses traveling in a medium where the group velocity exceeds c. And therefore, the distinction between the so-called 'phase velocity & group velocity' is shown experimentally to be useless and false.




Anonym: The distinction between group and phase velocity cannot be false. This results from the fact dw/dk is distinct from w/k. The distinction cannot be useless experimentally either, since it is widely used.




AAF: Well, Anonym; you can say that, and I won't object very much! wink.gif However, the whole PURPOSE of resurrecting Sommerfeld's old idea
http://www.bibsonomy.org/bibtex/259bde9d1dbe57ce257be37252eb6bfcd/vch
about the distinction between group & phase velocities, nowadays, is to impose an Einsteinian ultimate speed limit on the transmission of information while at the same time accepting superluminality of light waves as an experimental fact. The fore-mentioned NIST experiment disposes with that distinction as a means to achieve that absolute limit. And therefore, this old idea is useless, as far as the above purpose is concerned.




Anonym: 1) The work of Stenner does not contradict the paper you reference. 2) No information has been shown to propagate FTL. What remains then from your post? It remains that this is a quite interesting topic. What strikes the most me is the simplicity and generality of the initial concept, and the difficulty to analyse some experimental situations. FTL information, causality and SR are incompatible: this is very simple. Could the four-wave mixing process break the speed limit: that's much more subtle. Just read the last sentence of the original paper. http://arxiv.org/pdf/1204.0810v1.pdf . Experimentally: it is difficult to show any FLT communication. Stenner & all are considering a quantum correlation experiment, not to show FTL communication, but 'simply' to indemnify the correlation between emitter and receiver signals. In itself it proves that no FTL communication has been proven by Stenner. It also suggests, from the writing style that they do not expect any FTL communication to be proven. Theoretically: I think it is also difficult to analyse this experiment. My personal approach would be to try a full ab-initio simulation. This is no easy. This is not even classical physics, quantum mechanics is involved as well as maybe a bit of statistical physics. This paper does not deal with ab-initio simulation, but gives a feeling of what the development may look like: http://puhep1.princeton.edu/~mcdonald/examples/negativegroupvelocity.pdf




AAF: The work of Stenner et al does contradict the work of NIST; Anonym! Because it conludes that information cannot be sent at speeds greater than the speed of light [c]. That is on one hand. On the other hand, the current work of NIST concludes that superluminal 4-wave mixing is possible; and that is exactly what is needed to send information at speeds greater than [c] by simply using the well known techniques of Amplitude and frequency modulation.




Anonym: AAF, The link you provided does not work. I don't understand what you are talking about. You are invoking a purpose just as if it was a kind of conspiracy. That's just irrelevant. What do you want to prove? What your purpose? And are you only able to prove it by invoking a conspiracy you named "purpose". If you can, it must not be in the field of physics. But I even don't see you point! I can only guess that you are in need of some challenge. Maybe you have chosen to challenge the popular statement that "nothing could go FTL"? If this is your challenge, then it is a poor one. (no risk and no reward) I would suggest you a better challenge: - try to explain the original paper better than SciendeDaily - try to discuss if a signal can be sent FTL on this basis In addition, you could try to analyse the history of the FTL discussions. And after all, what does it really mean that "information cannot go FTL?". What is the meaning of the word "signal"?




Anon: >>What is the meaning of the word "signal"? the result of Einsteinian doubletalk is to lose meaning of words, since you are an advocate it is no wonder that you don't know what the words mean.




Anonym: As a tenant of Intelligent Design, anon should also believe that the vocabulary was intelligently created by an absolute god. So the meaning of words never changes and never needs any refinement. anon uses the bible for everything: from a simple dictionary to a TV set manual including a full course of physics. These bible readers are assholes.




Anon: >>These bible readers are assholes. that's still better than what you are.




AAF: YOUR 'bible readers' are so smart, Anonym & Anon; but you won't really know it until you run into some 'nutty' readers of other 'bibles'! [linked image]

What does it really mean that "information cannot go FTL"?

Within the context of Einstein's Relativity, it means no physical effect can travel faster than [c], otherwise this theory would not be able to give any coherent cause-effect explanation of anything. That is what they say. But, in my view, that is not the real problem. The real problem is that the Postulate of Constancy would become invalid; and when and if this Postulate becomes invalid, the theory of Relativity won't work at all.




Anonym: AAF, This could be of interest for you: http://www.lle.rochester.edu/media/publications/documents/theses/Bigelow.pdf





AAF: Thank you, Anonym; and I think this article entitled: Light breaking its own speed limit: how superluminal shenanigans work agrees with your views on this subject. The most important question on this topic is this: What is the physical mechanism that makes light travel at superluminal speeds in anomalously dispersive media, photonic crystals, and similar materials? At the present, this question cannot be answered, because one basic piece of information is still missing: There is no mention, in the NIST report and other experimental reports, of any speed measurements performed on the light pulses upon existing those special materials. Only after making these speed measurements, the true physical mechanism can be discovered.









 
 
Anonymous

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 21 2012, 4:31 AM 

AAF: The work of Stenner et al does contradict the work of NIST; Anonym! Because it conludes that information cannot be sent at speeds greater than the speed of light [c]. That is on one hand. On the other hand, the current work of NIST concludes that superluminal 4-wave mixing is possible; and that is exactly what is needed to send information at speeds greater than [c] by simply using the well known techniques of Amplitude and frequency modulation.


You are mistaken.

First of all, you can discard the journalist account in ScienceDaily: this is ********.

Second, you need to read the (free version of) the original paper:
http://arxiv.org/pdf/1204.0810v1.pdf
This paper doesn't mention any FTL communication.
The last sentense of the paper is the most revealing:

> In particular, one can hope to use the quantum
> correlations to examine experimentally which part of the
> input pulse is causally linked to the peak of the output pulse.

What does it mean?
At least it means that they do not know today
"which part of the input pulse is causally linked to the peak of the output pulse".
If they do not know this, they can't in no way claim any FTL communication.
And as these people are reasonable, they do not claim anything like that.

Moreover, a subpart of the same sentense is even more revealing.
This is it: "peak of the output pulse".
Remember that the "peak of the output pulse" is known since 100 year (exactly) to be irrelevant as far as communication is involved.

 
 
Anonymous

For AAF, please read this:

May 21 2012, 11:33 AM 

http://www.nist.gov/pml/div684/fast_light.cfm

Again! Better information than ScienceDaily, as should be expected from a first-hand source.

There are many interresting sentenses in this paper, together with some that I do not (yet) understand.
This one is relevant to our original discussion:

"Communications researchers have proposed that slow light could act as a sort of controllable delay line, or storage medium, for light carrying quantum information. Alternatively, the fast conjugate pulse that Letts group has observed might act as a way to advance the detection of quantum information, should the fast light retain quantum coherence. (NIST scientists emphasized that, while the information detection could be advanced, no information could actually travel faster than the speed of light and that, consequently, principles like causality in special relativity were always respected in these experiments.)"

As far as papers are concerned, this closes our debate: clearly no FTL communication.
Yet, we (at least myself) need a better understanding.
(J fyqfdu up mbvhife bu cz bopo gps uijt mbtu tfoufotf)

For example, I dare not understand this sentence:

"Laser Cooling and Trapping Group researcher Paul Lett and colleagues report in a forthcoming paper* in Physical Review Letters that this new method of generating fast light has resulted in a pulse that travels up to 50 ns faster over the length of a 1.7-cm cell than it would if it were moving through a vacuum."

Would you, AAF?

 
 
Anonymous

There is no Sciencedaily journalist

May 21 2012, 11:42 AM 

Just compare these:

http://www.sciencedaily.com/releases/2012/05/120503194223.htm

http://www.nist.gov/pml/div684/light-050212.cfm

So NIST did the job for SciencDaily.
Doesn't that look like advertisment?
Teasing common people and being careful with other scientists?
Fortunately, I won't turn mad for that.
I leave it to Pentcho Valev to become mad.

 
 
anon

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 21 2012, 2:36 PM 

>>>Fortunately, I won't turn mad for that.

Too late you are mad already.

NIST thinks Einstein is wrong.

 
 
Anonymous

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 21 2012, 2:57 PM 

"NIST scientists emphasized that, while the information detection could be advanced, no information could actually travel faster than the speed of light and that, consequently, principles like causality in special relativity were always respected in these experiments."

http://www.nist.gov/pml/div684/fast_light.cfm

You are uninformed unless you are an idiot.

 
 
AAF

Re: Researchers Develop New Way to Generate Superluminal Pulses

May 21 2012, 6:39 PM 







"Remember that the "peak of the output pulse" is known since 100 year (exactly) to be irrelevant as far as communication is involved."


I disagree, Anonym! wink.gif

The 'peak of the output pulse' is the most important
part of the Gaussian-modulated sinusoidal pulse:

http://www.mathworks.com/help/toolbox/signal/ref/gauspuls.html
[linked image]

A pulse without a peak is a dispersed pulse whose encoded information
has been lost for good.






 
 
 
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