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Scientists Freeze Pulse Of Light
Smitty825 writes "After slowing down light to slow speeds, scientists at Harvard University have been able to stop light for a very brief period of time without destroying its energy. The article explains how it is different from this previous light-stopping science story - this will hopefully help the development of quantum computers and ways to communicate over long distances without being eavesdropped on."
Oh...wait. Voids allow light to travel faster. shame on me. What color is stopped light if it retains its energy?
~mingust
I thought that light is a visual thing. How does one "eavesdrop" on light?
From excellent karma to terible karma with a single +5 funny post...
If the NSA supposedly managed to tap into fiber (light) what makes this guy so sure his studies would minimize/cut/halt the risk of eavesdropping? "Splice the line, and you cut off the light, at least momentarily," says Wayne Siddall, an optical engineer at Corning Fiber in Corning, N.Y. Even a second's interruption could be noticed by a cable's operator. Cable companies typically build systems with duplicate lines that take diverging routes, in case one of them is damaged or severed. One retired NSA optical specialist insists that the NSA devised a way to splice a fiber without being detected. "Getting into fiber is delicate work, but by no means impossible," the former specialist says. Neither he nor the NSA will discuss the matter further.
Spy agency taps into undersea cable
NSA Tapping Underwater Fiber Optics
And the list goes on and on. Bear in mind the NSA's date of achieving this, in comparison to the tech growth scale, I'd be willing to say that whatever Harvard is doing in being closely watched, if not already known.
MoFscker
Sounds like you could use it similar to the initial version of electronic memory (sort of a digital delay line), if it could be harnessed.
:-)
A few hundred-thousandths of a second is an eternity(*) for a photon. That's actually pretty impressive
Simon.
(*) Yes, for the pedants amongst us, I realise it's not actually an eternity. It's a figure of speech, for chrissake!
Physicists get Hadrons!
Could "Slow Glass" be coming? Bob Shaw wrote about glass that could slow down light so that it took years to pass through and the effects it had on society in his 1972 book Other Days, Other Eyes. Anyone interested in this stuff should hunt down a copy.
I once read an SF short story that featured windowpanes which light took decades to pass through - thereby letting you look at the past.
The story included the poignant scene of the protagonist looking out at his wife and child playing in the garden - but they had died 15 years earlier. The character used to hang around near the windows, hoping for glimpses of his dead wife, because he, of course, had no control over when he saw her; the windows would "replay the past" in strict linear sequence.
Does anyone know the name & author of the story?
In the story, the windowpanes were made of optical fibre nanotubes that were so tightly coiled up in the windows that the windows could accomodate tubes a few light-years long.
This research suggests more feasibly ways of doing this, though.
I thought speed of light was linked to time? If this is the case, what happens to time in this experiment? Apologies if I am being a twat.
Paul.
I think you're missing the point.
These experiments are all a stepping stone towards genuine quantum communication. Previous experiment such as those in Paris (by firing rhubidium through a photon of light)showed that scientists can no measure certain properties of light without destroying the photon, and then re-measure it. The problem was that for quantum communication, you need to disentangle 2 separate photons from an entangled state so that any change you make to one makes ann instantaneous change to the other, it's twin if you like and that can be done it seems. But, keeping the light fixed in a certain place is one of the tricky parts. If they ever succeed at refing these crystals to the extent that a photon can be kept in a deterministic state, then all you need is 2 of these crystals - you can imagine them being placed at opposite ends of our solar system, each crystal containing your premade entangled photon bouncing back and forth, with the crystal itself locked in some kind of black box (cavity).
Presumablt the crystals would have small atomic/sub/atomic sized pin holes to fire the rhubidium or other material through one of the crystals. The the phase shif of the rhubidium caused by this firing also occurs at the other photon (because they are entangled). Then when you measure the phase shift of the second crystal, the difference is twice as great (i.e. the first phase shift plus the second phase shift0 - hence you know at the other end of the solar system, that it was fired. Now all you need is a model, to measure
according to time, t. For example, one crystal could measure every odd microsecond, the other at every even microsecond.
Now you have a unary turing machine, communicating between the stars!!!.
Could this lead to harvisting light? As in, freeze large areas (100-1000m3) of light and then using the light to produce energy?
Im not pretending to know what im talking about but it sounds as if one day we'll be able to cut light right out of the sky for where we dont need light, like on the moon or other planets. I was going to say antartica or the ocean but then i thought we'd prolly all die in huge freek weather storms or feeze to death.
But being able to harvest light could be a pretty cool advancement for our growing energy needs. Maybe would could harvest it with huge satelites orbiting the sun and have the light transported back as high energy lazers?
Giving IE users a taste of their own medicine since 2005 - http://pods.-is-a-geek.net/
Oops, and forgot to mention,
Though Einstein, Podosky and Rosen were able to monitor the effects of QE (Quantum Entanglement), no scientists yet know how an entangled pair of photons can have this "weird" communication.
Some suspect a quantum bridge of some kind, whatever that would be..!
I like to think it is one of natures gifts, it is wnough that we can dream of its use and who knows, maybe someday use it.
So thats why eavesdropping would be imnpossible!!!
The only hope for an eavesdropper would be to secretly take over the disentanglement process an manufacture a third photon (for his/her self)
Then however communication would break down, because inevitably, the eaves dropper would measure his/her photon, creating an extra phase shift. Now communication between the 2 law-biding parties would have a triple phase shift, so they would immediately know someone is eavesdropping and cease communication. So, QE really would be the perfect way to communicate!
http://scienceworld.wolfram.com/physics CherenkovRadiation
what implications would this have?
One actually can travel faster than the speed of light in a certain medium. I hear it is common in nuclear reactors and results in what is termed as a sonic boom of sorts when the light actually catches up to the other particles.
Reading the study you linked to, it says that when the atomic excitation that makes this possible is converted back into light, the pulse can be propagated in either a forward or backward direction.
Which should mean that you could create a sort of time-delayed mirror, wouldn't it?
Hard to see how that would be useful, except perhaps as a gag of some sort.
(Ha! Hard to see! Get it?)
Is this truly the only Earth I can live on?
What about a man in the middle attack? You buy your entangled photon pair from my SneakyFactory. What I really sell you is two unrelated photons, while keeping their "actual" twins in my factory. Long before I delivered you your pair, I've set up my end of things to immediately record whatever comes in, and communicate it to the other photon.
Is there anything that stops this sort of attack? The only thing I can imagine is some sort of timing measurement..
-Zipwow
I don't know which is more depressing, that 2/3 didn't care enough to vote, or that 1/2 of those that did are crazy.
If I remember correctly, there is a very simple reason that communication via light would be secure -
In the quantum world, if you interact with the light, you change it in some way, no matter what, and since eavesdropping would involve interacting with the signal, the signal would not be exactly the same.
-- If an artist saw things as they truly are, they would cease to be an artist.
The generalized uncertainty principle basically says that two non-commuting operators have a commutator [A,B]=iC where i is the sqrt(-1), then a limit on the product of their uncertainties is delta_A*delta_B>=/2. Where delta_A is, as you indicated, a statistical calculation of the uncertainty, or standard deviation. This can be explicitly proven (and was actually one of the questions on my quantum mechanics midterm 2 years ago). (In case anyone is wondering, a commutator [A,B]=AB-BA. It is not generally zero, because A and B are operators, not variables. In programming talk, it's actually very similar to how ++c and c++ differ. Ie, it depends if the increment comes before/after the value is returned.)
This is most popular in terms of position/momentum, where the basic commutator of position/momentum operators is [x,p]=i*hbar. Thus, delta_x*delta_p>=hbar/2. Actually, the fact that [x,p]=i*hbar is one of the fundamental bases upon which most of quantum mechanics is based. (in case people are curious, in position space, momentum is referred to as the generator of translations, and thus will translate the position by some amount when it is measured. That's why position/momentum operators don't commute).
Energy and time are somewhat different. Position and momentum are specific operators. Energy is an eigenvalue of the Hamiltonian operator (sometimes). But time is a parameter, not an operator. So you cannot apply the generalized uncertainty relation here.
Now there is a rough uncertainty principle for energy/time, which goes as delta_E*delta_T>=hbar, but that isn't specifically well defined.
Finally, yes there can be local violations of conservation of energy. And this is due to the energy/time uncertainty. In other words, particles and antiparticles can spontaneously form out of the vacuum on VERY SMALL time scales. Ie, in such a small time scale, you have, at minimum, a large energy uncertainty. And thus within this uncertainty energy is conserved. Thus, local violations of energy conservation.
make world, not war