Researchers develop way to control speed of light, send it backward

light
Credit: Petr Kratochvil/public domain

University of Central Florida researchers have developed a way to control the speed of light. Not only can they speed up a pulse of light and slow it down, they can also make it travel backward.

The results were published recently in the journal Nature Communications.

This achievement is a major step in research that could one day lead to more efficient optical communication, as the technique could be used to alleviate data congestion and prevent information loss. And with more and more devices coming online and data transfer rates becoming higher, this sort of control will be necessary.

Previous attempts at controlling the have included passing light through various materials to adjust its speed. The new technique, however, allows the speed to be adjusted for the first time in the open, without using any pass-through material to speed it up or slow it down.

"This is the first clear demonstration of controlling the speed of a light in ," said study co-author Ayman Abouraddy, a professor in UCF's College of Optics and Photonics. "And it opens up doors for many applications, an optical buffer being just one of them, but most importantly it's done in a simple way, that's repeatable and reliable."

Abouraddy and study co-author Esat Kondakci demonstrated they could speed a pulse of light up to 30 times the speed of light, slow it down to half the speed of light, and also make the pulse travel backward.

The researchers were able to develop the technique by using a special device known as a to mix the space and time properties of light, thereby allowing them to control the velocity of the pulse of . The mixing of the two properties was key to the technique's success.

"We're able to control the of the pulse by going into the pulse itself and reorganizing its energy such that its space and time degrees of freedom are mixed in with each other," Abouraddy said.

"We're very happy with these results, and we're very hopeful it's just the starting point of future research," he said.


Explore further

Flying focus: Controlling lasers through time and space

More information: H. Esat Kondakci et al. Optical space-time wave packets having arbitrary group velocities in free space, Nature Communications (2019). DOI: 10.1038/s41467-019-08735-8 , www.nature.com/articles/s41467-019-08735-8
Journal information: Nature Communications

Citation: Researchers develop way to control speed of light, send it backward (2019, April 4) retrieved 22 April 2019 from https://phys.org/news/2019-04-researchers-develop-way-to-control.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
16517 shares

Feedback to editors

User comments

Apr 04, 2019
Combine this with Quantumly entangled photons that you are beaming half to other places in the solar system while maintaining the other half locally where you can flip states all the way up until the signal is received and you have yourself a means of communicating in real time, even across light hours. I would assume this would be more useful for overcoming satellite lag in the short term but would quickly become the standard for all communications if it proved workable.

Apr 04, 2019
From the article:
they could speed a pulse of light up to 30 times the speed of light,
Is this the same way a water wave 'impact front' can 'travel' at fantastic speed when two opposing wave fronts meet at a slight angle and the 'impact point 'travels' along the line of intersection from one end to the other? Or do they actually speed up the light pulse as they claimed? If so, they do not explain how they can do that in 'free space' (as opposed to media-transmitted contexts).

ps: Or Is it that they can do that only when the calendar flips to April? Just asking! :)

Apr 04, 2019
From the article:
they could speed a pulse of light up to 30 times the speed of light,
Is this the same way a water wave 'impact front' can 'travel' at fantastic speed when two opposing wave fronts meet at a slight angle and the 'impact point 'travels' along the line of intersection from one end to the other? Or do they actually speed up the light pulse as they claimed? If so, they do not explain how they can do that in 'free space' (as opposed to media-transmitted contexts).

ps: Or Is it that they can do that only when the calendar flips to April? Just asking! :)


No this is using the spooky action at a distance to change one half of an entangled pair that happens to be light hours away by changing the local half of that entanglement. At no point do any photons travel faster than light, but the end result is instant communication. It isn't my fault that quantum physics allows this seeming loophole. High-speed stock traders would pay for this just to get 2MS less lag.

Apr 04, 2019
@Jeffhans1.
No this is using the spooky action at a distance to change one half of an entangled pair that happens to be light hours away by changing the local half of that entanglement. At no point do any photons travel faster than light, but the end result is instant communication. It isn't my fault that quantum physics allows this seeming loophole. High-speed stock traders would pay for this just to get 2MS less lag.
There are two aspects involved. One is the 'transmission' of quantum entanglement info, which already is purported to occur 'instantaneously' over said distance...so they cannot have 'speeded up' THAT at all. And then there is the alleged light pulse 'speed-up' mechanism which isn't explained....since the info is already supposed to be 'transmitted' instantaneously.

So, can you explain how they can speed it up to 30 times lightspeed from an already supposed INSTANTANEOUS or INFINTE 'speed' at which quantum entanglement allegedly operates, mate? Thanks.

Apr 04, 2019
This piece sounds like an article in The Onion...

Apr 04, 2019
So, can you explain how they can speed it up to 30 times lightspeed from an already supposed INSTANTANEOUS or INFINTE 'speed' at which quantum entanglement allegedly operates, mate? Thanks.

No, I can't explain their methods. Assuming they are correct in their conclusions though, the speed of light is not limited by our assumed upper limit. My discussion was about slowing light down and storing it locally, which has been demonstrated numerous times in labs all around the world using various materials.
Apparently, it doesn't work with current techniques at least:
https://www.nbcne...-n336766

Apr 05, 2019
Light sabers anyone?

Apr 05, 2019
I was looking at the double slit quantum eraser experiment and thought it might make a valid (but expensive) method of communicating over interplanetary distances.
In real time (for strange definitions of real time).
After all, Mars, for instance, does not share time with Earth (different gravity).
I think that is a thing to do in the future though; not right now.

Apr 05, 2019
Some instagram user @quanta_gramm made a post about this article, and copied the entire article in the caption. I don't know if they are allowed to do this

Apr 05, 2019
*Sigh* this is group velocity. Not velocity of individual photons.
https://en.wikipe...velocity
It's like passing a laserpointer accross the face of the moon.
Can the bright spot on the moon APPEAR to move faster than light? Yes.
Does anything in this setup (including information transmission) move faster than light? No.

Speed of light limits aren't broken, here. It's achieved with a (very clever) modulation of the beam characteristics with the magnetic and electric fields not at right angles to the direction of propagation but canted sharply forwards/aft.

(Full paper is linked in the article, BTW...so all you nutjobs could have saved your time and just read it before posting your ludicrous comments)

@Jeff, icecycle: No. Entanglement does not allow faster than light communication. Read up on what information transmission IS before making such ridiculous statements. (Particularly the difference between classical information and quantum information)

Apr 05, 2019
No this is using the spooky action at a distance to change one half of an entangled pair that happens to be light hours away by changing the local half of that entanglement.


No. If you CHANGE one half of an entangled pair (i.e. set it to some value in an attempt to encode some message on it) this has no effect on the other one. In that moment you are breaking entaglement.
Only when you MEASURE a (still) entangled entity do you know something about the other one.

(Actually this is the most beautiful proof that the act of encryption doesn't constitute adding information, because if you know that entangled pairs are complementary you can use them for encryption/decryption even though their states are measurd great distances apart. This is the basis of quantum encryption systems.)


Apr 05, 2019
Combine this with Quantumly entangled photons that you are beaming half to other places in the solar system while maintaining the other half locally where you can flip states all the way up until the signal is received and you have yourself a means of communicating in real time, even across light hours. I would assume this would be more useful for overcoming satellite lag in the short term but would quickly become the standard for all communications if it proved workable.


Correct me if I'm wrong, but observing an entangled photon breaks its entanglement, no? This is why we cannot use them to communicate.

Apr 05, 2019
Correct me if I'm wrong, but observing an entangled photon breaks its entanglement, no?

When you observe (i.e measure) then you get the knowledge about its state AND the state of the other entangled entity of the pair.

Entanglement is broken to the degree of measurement, because you can do something funky like 'weak' measurement in which you only measure the state to a certain degree of probability.
In this case entangelemnt is only partially broken (the correlation between the state of the entity and it's counterpart is weakened but not fully destroyed).

And no, before anyone asks, you cannot use this for FTL information transmission either.

For those still doubting consider/look up why the unit for quantum information (the qbit) is not the same as the one for classical information (the bit)


Apr 05, 2019
*Sigh* this is group velocity.
Yes, I was expecting to see either/both "phase velocity", "group velocity" somewhere in the article. "pulse" was the tip-off but I had to go to the original paper and look at the abstract. I recommened looking at the fourth animation down of the Wikipedia article "Phase Velocity".

These seeming superluminal-like items hit the popular press over the past many decades on a semi-regular basis.

Apr 05, 2019
This article is so bogus. I looked at multiple related articles, and saw things said like manipulating time and space. The only article I could find that eluded to a technical explanation said something about splitting up the light color spectrum, and made it sound like they redirected them at different angles through a lens of some sort. I wanted to add sarcasm in saying they reverse light with a mirror, which isn't reversal at all it is redirection, as is the explanation. Smoke and mirrors. This article must of originally come out on April Fool's Day and been reported a day or two late.

Apr 05, 2019
When you observe (i.e measure) then you get the knowledge about its state AND the state of the other entangled entity of the pair.
This is only my opinion on the matter, but I've long suspected that the quantum entanglement attribute of the pair is a singular—non-local, atemporal—SHARED property, whether having the same or opposite sign, on measurement, of the respective local particles. This is a realist model, of course, and perhaps rather unparsimonious, if not downright silly. I just feel my freedom of thought allows me to choose which alternatives are LESS silly under the constraints of the baffling world of quantum phenomena.

Apr 05, 2019
This article must of [have] originally come out on April Fool's Day and been reported a day or two late.
(correction inserted)
No, the original, which is cited below the article, came out well before April Fool's, and the citation does include the title's phrase 'group velocities', where we smell the rat. 'Group velocity' is always a dead giveaway, and ought to be mentioned in a popular article, and elaborated on. But it has nothing to do with Fool's day. There have been dozens of related such articles over the decades.

Apr 05, 2019
but I've long suspected that the quantum entanglement attribute of the pair is a singular

Well, yes. The point of entanglement is that the description of one of the pair is linked to the decription of the other one. i.e. they aren't completely separable.
You have ONE attribute that describes both.

Apr 05, 2019
Evidence of changing Einstein is in front of you and you refuse to see. What of the phrase about the Holocaust that none were so blind as those that refused to see......for if they actually loooked at the evidence of an ongoing Holocaust, then the responsibility to act would have been upon them. And THAT meant war, that which they could not bear to prepare for. That paralyzed France and other Europeans to not act.

Similar here. New physics stares us now in the face. An unknown out of our comfort zone. Where the new fear is now there is no hard and fast rule. Now communication IS possible with lattice QCD research. Now can be seen why we get no interstellar commo from ordinary light/EM waves.

Logically there ARE standards. Aliens communicate, and travel..., and trade. Each starfaring species or groups may have their own secure commo. Steven Hawking said if something like this can happen once, then can be done millions of times..or no limit at all. Area 51 KNOWS

Apr 05, 2019
Similar here. New physics stares us now in the face.

Read the paper. Not even the authors say this is new physics in any way shape or form. This is (very clever) use of known physical principles and neither QM nor relativity are violated, here

Seriously. if you want to claim that something is a certain way then you need to start understanding what you're talking about. Otherwise you're just making yourself look like a doofus.

Now communication IS possible with lattice QCD research.

Erm whut? Lattice QCD has nothing to do with this (and nothing to do with long range information transmission at all).

You are just stringing together random googled sciency sounding words. It's ridiculous.
(and impresses absolutely zero people. If anything, you're just hoisting a huge "I don't know what I'm talking about" sign over your head and making sure it's conserved on the internet for all eternity)

Apr 05, 2019
"Researchers develop way to control speed of light, send it backward"

Comical at best, and comical to say the least.........

Apr 06, 2019
"*Sigh* this is group velocity. Not velocity of individual photons."

I sighed too when I read the title, Click baits and crackpots will always be with us, but in some areas they combine to the perfect storm of muddying the waters.

Thx to you , danR and the rest for tidying up the area!

Apr 06, 2019
@torbjorn_b_g_larsson
@antialias_physorg.

@torbjorn_b_g_larsson.
Thx to ...and the rest for tidying up the area!
You're welcome, mate! And I agree, these 'click bait' headings and deliberately misleading/sensational 'articles' by so-called 'science writers/journalists' etc are 'a pain in the ars-e' which contributes to much confused comments from those not alert to such 'publicity devices' to attract clicks rather than explain anything 'new' worth explaining.

@antialias_physorg. Yes, I also pointed out that it was something like what you said; only I used the non-parallel, opposing two-wave collision 'impact point' to illustrate the 'traveling artefact' aspect. Thanks for your post to help highlight that aspect. Cheers. :)

Apr 08, 2019
Lol, this looks like a lot of woo. In my interaction with UCF in 2010, I got the impression that, I was dealing with all bloody jokers

Apr 08, 2019
*Sigh* this is group velocity. Not velocity of individual photons.


I sighed too when I read the title, Click baits and crackpots will always be with us, but in some areas they combine to the perfect storm of muddying the waters.

It was more a *sigh* towards the - oh so very predictable - slew of comments that misunderstood/misconstrued the content of the article rather than at the article itself (which I thought was quite clearly written).

Even though the title is a bit click-baity I think a real "backwards-in-time" or "faster than light" type of story make a weeee bit bigger impact in the media.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more