from the a-few-drinks-shy-of-incoherence dept.
60-year-old limit to lasers overturned by quantum researchers:
A team of Australian quantum theorists has shown how to break a bound that had been believed, for 60 years, to fundamentally limit the coherence of lasers.
The coherence of a laser beam can be thought of as the number of photons (particles of light) emitted consecutively into the beam with the same phase (all waving together). It determines how well it can perform a wide variety of precision tasks, such as controlling all the components of a quantum computer.
Now, in a paper published in Nature Physics, the researchers from Griffith University and Macquarie University have shown that new quantum technologies open the possibility of making this coherence vastly larger than was thought possible.
"The conventional wisdom dates back to a famous 1958 paper by American physicists Arthur Schawlow and Charles Townes," said Professor Howard Wiseman, project leader and Director of Griffith's Centre for Quantum Dynamics.
[...] "They showed theoretically that the coherence of the beam cannot be greater than the square of the number of photons stored in the laser," he said.
"In our paper, we have shown that the true limit imposed by quantum mechanics is that the coherence cannot be greater than the fourth power of the number of photons stored in the laser," said Associate Professor Dominic Berry, from Macquarie University.
"When the stored number of photons is large, as is typically the case, our new upper bound is much bigger than the old one."
Journal Reference:
Travis J. Baker, Seyed N. Saadatmand, Dominic W. Berry, et al. The Heisenberg limit for laser coherence, Nature Physics (DOI: 10.1038/s41567-020-01049-3)
(Score: 0, Offtopic) by legont on Wednesday October 28 2020, @03:54PM (16 children)
My messages a censored by the admins
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: -1, Offtopic) by Anonymous Coward on Wednesday October 28 2020, @04:00PM
Not again, ari, please... Oh, wait... (large grin)
(Score: 1) by DannyB on Wednesday October 28 2020, @04:09PM (10 children)
If possible, you can hold your breath while waiting for the admins to correct this injustice. Meanwhile you can read about how Trump's campaign website hacked [axios.com]
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(Score: 2) by legont on Wednesday October 28 2020, @04:24PM (9 children)
Can I say "conspiracy" meantime? Looks definitely like it given the date of the year.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by takyon on Wednesday October 28 2020, @04:56PM (8 children)
What was censored, legunt?
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 2) by legont on Wednesday October 28 2020, @09:27PM (7 children)
It turns out that if a message is modded down to -1, the thread that it started is not shown even if the messages in it have way higher mod. I did not know; and I think it is wrong.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by HiThere on Wednesday October 28 2020, @11:04PM (5 children)
If you browse at -1 this doesn't happen.
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
(Score: 2) by Immerman on Thursday October 29 2020, @02:05AM (4 children)
It might just be the green site, but I'm pretty sure I've seen it here too, where even browsing at -1 there will be messages missing, while their replies still appear with the additional level of indentation (but no extra border)
(Score: 2) by The Mighty Buzzard on Thursday October 29 2020, @01:10PM (3 children)
Spam messages should auto-collapse always. Browsing at -1 nothing else should collapse. If you're sure and you can reproduce it, let me know how.
My rights don't end where your fear begins.
(Score: 2) by Immerman on Thursday October 29 2020, @01:28PM (2 children)
I'm not talking about collapse, I'd be okay with that. I'm talking about the message is *gone* - no header to click on to expand it if I wanted to. Replies are still shifted right as though they were inside the parent comment-border, but there's no border, no header, no other sign that the parent comment ever existed (aside from the replies themselves).
I'll try to remember to send a screenshot and details next time I notice it. It's not exactly something I can recreate since I have no apparent causal control, but I can at least confirm whether it happens in other browsers or if it's something to do with my browser or account settings.
(Score: 2) by The Mighty Buzzard on Friday October 30 2020, @02:05AM (1 child)
Now that is not supposed to happen in any view mode. Next time grab a screenshot and note the time of the page load as well, please. Then hit refresh and see if it clears up. Given the code and outdated versions of third party software we're working with, it's not at all surprising that bugs occasionally crop up.
My rights don't end where your fear begins.
(Score: 2) by Immerman on Friday October 30 2020, @09:35PM
Will do.
I do recall that neither refresh nor even completely restarting the browser resolved the problem.
(Score: 2) by The Mighty Buzzard on Thursday October 29 2020, @01:15PM
In Threaded-TOS, that's where the Breakthrough setting comes in. It makes higher scoring comments show up even if the parent is collapsed due to a score below your Threshold.
In Threaded-TNG, any comment >= Threshold (except Spam) should be expanded, no matter what.
My rights don't end where your fear begins.
(Score: 2) by Freeman on Thursday October 29 2020, @05:19PM (3 children)
No, your messages aren't being censored by the admins. You're coming through just fine. I found your "censored" thread just fine and commented on it.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 2) by legont on Thursday October 29 2020, @11:23PM (2 children)
It appears that if a thread is started by AC and that AC message was moderated to -1, the thread is behaving funny. I am new to this issue and can't provide robust evidence. However, I am not going to answer AC messages for now for this particular reason.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by Freeman on Monday November 02 2020, @03:47PM (1 child)
Considering what others have said about it, it sounds like expected behavior. Whether that's, specifically how AC threads are handled or how any thread modded down to -1 is handled, I'm a little uncertain. From what I could tell it was being handled correctly. You just weren't able to see it due to not allowing lower modded things to be shown, perhaps?
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 3, Interesting) by legont on Tuesday November 03 2020, @12:31AM
Yes, this was the case, sorry. Having said that, I am no longer replying to any AC comments.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by DannyB on Wednesday October 28 2020, @04:14PM (3 children)
Is the divergence of the laser beam related to coherence? I didn't know there were degrees of coherence. Does higher coherence mean the beam would diverge less?
I read something like the following many years ago, possibly on Usenet.
From town point laser at mountain. Go to that location, and when you walk into the beam, suddenly the bright spot of the laser back in town is visible, but not so bright as damage eyes. Person then said they could walk back and forth and measure how many feet wide the beam was. Fifteen feet, if I remember correctly.
You can assume that is absolutely as truthful as anything else that one might read somewhere online decades ago.
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(Score: 4, Informative) by ikanreed on Wednesday October 28 2020, @04:39PM
Not really.
Coherence is a measure of variation in wavelength and amplitude.
Traveling through a medium like air, that does slightly affect divergence due to varying speeds of light in a medium at different wavelengths.
Divergence is mostly determined by the shape of the amplification chamber of the laser.
(Score: 0) by Anonymous Coward on Wednesday October 28 2020, @04:58PM
I found this article on what coherency means: http://amasci.com/miscon/coherenc.html [amasci.com]
Which, if I understand correctly, is essentially saying that the coherency of light is a measure of how closely the light source resembles a single point source.
Given that explanation, it should follow that the coherency of the light is one of the parameters that influences how effectively you can use things like lenses and mirrors to direct the light, notwithstanding weird quantum effects like diffraction. So I think the answer is "yes", divergence is related to (in)coherence but not the same thing.
From the article:
(Score: 5, Interesting) by bd on Wednesday October 28 2020, @07:11PM
Basically, there are two independent concepts of coherence: temporal coherence and spatial coherence.
Spatial coherence determines how low of a beam divergence you can achieve, and how small you can focus your light.
This is exactly what you are thinking about.
Every light beam has to diverge, as a converging and diverging beam is simply the shape of solutions for Maxwell's
equations. The more ideal (spatially coherent) the light source, the lesser the beam divergence is possible.
Temporal coherence means how ideal of a sine wave the electric field of the beam is.
Think of electrical oscillators. An atomic clock has better temporal coherence than a real-time clock in a computer.
In an ideal world, a laser beam would be represented by a single sinus function. Of course, in the real world, nothing
is a single sine wave, as there is always noise and frequency instability. A spectral line therefore is never infinitely narrow.
The Schawlow-Townes Linewidth is a theretical noise limit, if no other noisy processes were present in the laser.
This is what these researchers have theoretically cheated. I don't think it will lead to better lasers, because we can't even
get to the original limit with real lasers.
(Score: 2, Funny) by Anonymous Coward on Wednesday October 28 2020, @04:38PM (8 children)
Does this mean the remote control will work faster? It seems like the photons have slowed down over the years. My TV used to switch on immediately when I pressed the button but now it goes takes about 2 minutes. Finally something useful from all that science funding - congrats to the Austrians.
(Score: 3, Insightful) by DannyB on Wednesday October 28 2020, @05:41PM (7 children)
Maybe the increasing slowfulness of your TV is due to all of the software updates?
TVs have historically needed a lot of software updates. Especially in the early NTSC days. (Not The Smartest Choice, Never The Same Color)
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(Score: 0) by Anonymous Coward on Wednesday October 28 2020, @07:07PM (6 children)
"TVs have historically needed a lot of software updates."
My old CRT T.V. never needed an update.
Of course we eventually trashed it because now you need a cable box for each feed. Two of our T.V.s are 'smart' TVs and one of them no longer has updates because of planned obsolescence. It still mostly works though but it has a few quirks with Youtube and Netflix since it's no longer up to date.
(Score: 0) by Anonymous Coward on Wednesday October 28 2020, @07:10PM (1 child)
(same poster)
and we have a Roku that we use with our Plasma T.V.
(Score: 1, Funny) by Anonymous Coward on Thursday October 29 2020, @01:36AM
This is fascinating. What other aging electrical appliances do you own or have you owned in the past?
(Score: 2) by VLM on Thursday October 29 2020, @01:20PM (3 children)
Expect a lot more with the whole youtube-dl debacle
(Score: 2) by DannyB on Thursday October 29 2020, @03:26PM (2 children)
Suppose for a moment, that maybe the [RI|MP]AA-holes demand YouTube to "do something!" and encrypt their content somehow? So YouTube does something to make it non trivial to download their content, but doesn't make it so difficult that it cannot be reverse engineered.
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(Score: 2) by VLM on Monday November 02 2020, @01:53PM (1 child)
Would not disagree with you, but I'd embrace and extend your remarks with respect to I think the RIAA/MPAA types are merely tools for youtube to cooperatively push strong encryption for their legacy TV network service, that one that costs $65/month and includes all the boomer-era TV networks.
(Score: 2) by DannyB on Monday November 02 2020, @02:47PM
That theory could be true. Yet it is not mutually exclusive with other theories. The MPAA/RIAA pre-date YouTube. And their insane behavior predates YouTube. The RIAA sued Diamond Rio (long, long ago) for the illegal act of merely creating and selling an mp3 player device. MP3 files could come from legal sources.
To transfer files: right-click on file, pick Copy. Unplug mouse, plug mouse into other computer. Right-click, paste.