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Science

Scientists Freeze Pulse Of Light 343

Posted by simoniker
from the mr-bigglesworth-looks-on dept.
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."
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Scientists Freeze Pulse Of Light

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  • by mingust (726690) on Thursday December 11, 2003 @05:43AM (#7688179)
    Oh...wait. Voids allow light to travel faster. shame on me. What color is stopped light if it retains its energy?
  • Very interesting... (Score:4, Interesting)

    by twoslice (457793) on Thursday December 11, 2003 @05:44AM (#7688189)
    development of quantum computers and ways to communicate over long distances without being eavesdropped on.

    I thought that light is a visual thing. How does one "eavesdrop" on light?

  • by segment (695309) <sil@politrix. o r g> on Thursday December 11, 2003 @05:49AM (#7688213) Homepage Journal
    Harnessing light particles to store and process data could aid the still distant goal of so-called quantum computers, as well as methods for communicating information over long distances without risk of eavesdropping.

    But today the NSA's snooping capabilities are in jeopardy, undermined by advances in telecommunications technology. Much of the information the agency once gleaned from the air waves now travels in the form of light beams through fiber-optic cables crisscrossing continents and ocean floors. That shift has forced the NSA to seek new ways to gather intelligence -- including tapping undersea cables, a technologically daunting, physically dangerous and potentially illegal task.

    In the mid-1990s, the NSA installed one such tap, say former intelligence officials familiar with the covert project. Using a special spy submarine, they say, agency personnel descended hundreds of feet into one of the oceans and sliced into a fiber-optic cable. The mixed results of the experiment -- particularly the agency's inability to make sense of the vast flood of data unleashed by the tap -- show that America's pre-eminent spy service has huge challenges to overcome if it hopes to keep from going deaf in the digital age.

    Details of the NSA cable-tapping project are sketchy. Individuals who confirm the tap won't specify where or when it occurred. It isn't known whether the cable's operator detected the intrusion, though former NSA officials say they believe it went unnoticed. Nor is it known whether the NSA has attempted other taps since. Efforts to intercept all sorts of signals -- ranging from military radar to international phone calls -- are among the most highly classified U.S. government operations. Leaking information about interception methods is a federal crime punishable by imprisonment.
    [Source [politrix.org]]

    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 [com.com]

    NSA Tapping Underwater Fiber Optics [slashdot.org]

    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.

  • Light RAM (Score:5, Interesting)

    by Space cowboy (13680) on Thursday December 11, 2003 @05:49AM (#7688214) Journal
    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!
  • by Pond823 (643768) on Thursday December 11, 2003 @05:58AM (#7688244)
    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.
  • by segment (695309) <sil@politrix. o r g> on Thursday December 11, 2003 @05:59AM (#7688249) Homepage Journal
    Good old fashioned history [slashdot.org]... Now only I could get my damn old UID [slashdot.org] back... Taco?

    Submarine cable interception

    Submarine cables now play a dominant role in international telecommunications, since - in contrast to the limited bandwidth available for space systems - optical media offer seemingly unlimited capacity. Save where cables terminate in countries where telecommunications operators provide Comint access (such as the UK and the US), submarine cables appear intrinsically secure because of the nature of the ocean environment. 49. In October 1971, this security was shown not to exist. A US submarine, Halibut, visited the Sea of Okhotsk off the eastern USSR and recorded communications passing on a military cable to the Khamchatka Peninsula Halibut was equipped with a deep diving chamber, fully in view on the submarine's stern. The chamber was described by the US Navy as a "deep submergence rescue vehicle". The truth was that the "rescue vehicle" was welded immovably to the submarine. Once submerged, deep-sea divers exited the submarine and wrapped tapping coils around the cable. Having proven the principle, USS Halibut returned in 1972 and laid a high capacity recording pod next to the cable. The technique involved no physical damage and was unlikely to have been readily detectable.

    The Okhotsk cable tapping operation continued for ten years, involving routine trips by three different specially equipped submarines to collect old pods and lay new ones; sometimes, more than one pod at a time. New targets were added in 1979. That summer, a newly converted submarine called USS Parche travelled from San Francisco under the North Pole to the Barents Sea, and laid a new cable tap near Murmansk. Its crew received a presidential citation for their achievement. The Okhotsk cable tap ended in 1982, after its location was compromised by a former NSA employee who sold information about the tap, codenamed IVY BELLS, to the Soviet Union. One of the IVY BELLS pods is now on display in the Moscow museum of the former KGB. The cable tap in the Barents Sea continued in operation, undetected, until tapping stopped in 1992.

    During 1985, cable-tapping operations were extended into the Mediterranean, to intercept cables linking Europe to West Africa. (30) After the cold war ended, the USS Parche was refitted with an extended section to accommodate larger cable tapping equipment and pods. Cable taps could be laid by remote control, using drones. USS Parche continues in operation to the present day, but the precise targets of its missions remain unknown. The Clinton administration evidently places high value on its achievements, Every year from 1994 to 1997, the submarine crew has been highly commended.(31) Likely targets may include the Middle East, Mediterranean, eastern Asia, and South America. The United States is the only naval power known to have deployed deep-sea technology for this purpose.

    Miniaturised inductive taps recorders have also been used to intercept underground cables.(32) Optical fibre cables, however, do not leak radio frequency signals and cannot be tapped using inductive loops. NSA and other Comint agencies have spent a great deal of money on research into tapping optical fibres, reportedly with little success. But long distance optical fibre cables are not invulnerable. The key means of access is by tampering with optoelectronic "repeaters" which boost signal levels over long distances. It follows that any submarine cable system using submerged optoelectronic repeaters cannot be considered secure from interception and communications intelligence activity.

  • by Alphanos (596595) on Thursday December 11, 2003 @06:07AM (#7688277)
    Disclaimer: I have not read the article since I don't know enough physics yet to be able to understand its significance:).

    That said, I got the impression from the post that this could somehow be beneficial to quantum cryptography. If I understand correctly, the idea behind quantum cryptography is that as long as you have a direct optical line to whoever you're transmitting to, it is physically impossible for undetected eavesdropping to occur. This is because the nature of the system is such that a single observation of the signal will change it in such a way that it cannot be reconstructed. Perhaps advances in our understanding of light will allow this to function over the internet, where we don't have direct lines to everyone we want to transmit to.

  • by pnagel (107544) on Thursday December 11, 2003 @06:37AM (#7688376)
    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.
  • by Otto (17870) on Thursday December 11, 2003 @07:26AM (#7688502) Homepage Journal
    Interesting story, I grant you, but if such a thing existed, you'd have to wonder at the temperature the glass would reach after absorbing light for a few years. It'd be possible to do something similar to it using other methods, but I doubt the possibility of doing it using anything similar to the methods described in the book.
  • 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.
  • by eggplantpasta (74715) on Thursday December 11, 2003 @07:37AM (#7688528) Homepage
    No. The lack of eavesdropping refers to the quantum properties of entangled photons used to encrypt communications in a theoretically unbreakable way. See here [eetimes.com]. There was also a slashdot story on this a few years ago.
  • by 505 (183073) on Thursday December 11, 2003 @07:54AM (#7688570) Homepage
    Bob Shaw is one of my favourite writers. I liked the Slow Glass stories. I don't think slow glass is coming any faster, because there are considerable problems to solve besides slowing light. Suppose we have a manageable slab of material that stores light for years. What about the optics?

    I suspect that looking at other days through a two-year slab of 'flat' slow glass would be like looking through a tunnel two light years long. Perhaps you could do something with fancy optics, maybe integral to the slab.

    Small irregularites currently quite acceptable on (say) astronomical mirrors would result in different parts of the images emerging at different times. Would the images be usable? Would slow glass transmit all frequencies of visible light at the same speed?
  • by essreenim (647659) on Thursday December 11, 2003 @07:58AM (#7688586)
    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!!!.

  • Harvest time (Score:4, Interesting)

    by POds (241854) on Thursday December 11, 2003 @08:08AM (#7688620) Homepage Journal
    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?
  • More Entanglement. (Score:3, Interesting)

    by essreenim (647659) on Thursday December 11, 2003 @08:11AM (#7688631)
    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!

  • by jabberjaw (683624) on Thursday December 11, 2003 @08:32AM (#7688697)

    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.

  • by corebreech (469871) on Thursday December 11, 2003 @08:36AM (#7688710) Journal
    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?)
  • by CommandNotFound (571326) on Thursday December 11, 2003 @09:26AM (#7688911)
    Hard to see how that would be useful, except perhaps as a gag of some sort.

    I would expect that any method to slow/store light would be useful in networking. Essentially, one could then queue and route light as packets without converting them to electrons via a router, which is probably how it's done now.
  • Re:Light RAM (Score:1, Interesting)

    by Anonymous Coward on Thursday December 11, 2003 @11:02AM (#7689660)
    A few hundred-thousandths of a second is an eternity(*) for a photon. That's actually pretty impressive :-)
    Actually for the photon it would be a fraction of an infinitesimal span of time. Just because it's small doesn't mean it experiences time an an increased rate. If you recall relativity, the faster one moves, the faster events outside of you seem to occur (for example, fly away in a space ship really fast, and when you come back the earth will have aged much more rapidly). Thus the ticking of the imaginary hundred-thousandths hand on the clock will occur even more frequently as you travel at high speeds. With light you take this to the limit and find that all eternity passes the photon by in less than the blink of an eye.

    It also makes me wonder if the time dilation effects of relativity are what keep photons "alive." It is known that if you accelerate unstable particles, their half lives become extended (at least to our timeframe). Maybe photons should decay very rapidly, but time dilation at the speed of light stretches this out to eternity. This would be why atoms can absorb a photons energy; they bring it to a stop and then it instantly decays. Then again, seeing as they've slowed down light before (or did they simply increase the path length by having it bounce around a lot?), I'm probably talking out of my ass on this one.
  • by SpaceJunkie (579366) on Thursday December 11, 2003 @11:56AM (#7690161) Homepage Journal
    Which leads to thoughts of using a similar idea as a power storage system. Exactly how much energy as light passes through a window in one day?

    Any physics buffs out there care to comment on that?
  • by gnalle (125916) on Thursday December 11, 2003 @01:35PM (#7691101)
    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.

    Do you have a reference for this? I feel stongly convinced that you cannot use the EPR experiment to transfer information at speeds that are faster than light speed. (Here information means that the people in Solar system A know that the people in Solar system B have performed a meassurement)

    However if physicists at Solar system A and Solar system B perform a meassurement at the same time, then their reasults will be correllated (and disbobey Bell's inequalities).

  • Man in the middle? (Score:4, Interesting)

    by zipwow (1695) <zipwowNO@SPAMgmail.com> on Thursday December 11, 2003 @01:46PM (#7691214) Homepage Journal
    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
  • by muchmusic (45065) <me@e v a n m . net> on Thursday December 11, 2003 @01:58PM (#7691338) Homepage
    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.
  • by wass (72082) on Thursday December 11, 2003 @02:51PM (#7691894)
    You're on the right track, but the energy/time uncertainty relation doesn't really follow from the generalized uncertainty principle.

    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.

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