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Science

Quantum Holography 207

Posted by Hemos from the peering-into-the-cat dept.
Buzz Skyline writes "Physicists succeed where psychics fail. Researchers from Boston University propose a quantum holography system that can construct 3d images of objects sealed in closed containers. Could it lead to quantum luggage scanners at the airport?"
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Quantum Holography More

Quantum Holography

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  • Schroedinger's Cat (Score:5, Funny)

    by gblues ( 90260 ) on Wednesday December 05, 2001 @04:46PM (#2661441)
    Great! Now we'll be able to tell Schroedinger once and for all whether his stupid cat is dead or not.

    Nathan
    • yeah, what implications will this have on that tried and true metiphor? by doing this, we are not realy observing the object directly, we are indirectly observing it. so does this destroy the uncertanty priciple or is this considered direct observation?
      • We are observing the object, period. If it's observed, then it completely destroys the principle.

        Duh :)
        • it seems to me that we are just observing the interactions of photons that we send into the box. not looking at the object in any way.
          • Uh...that's how we 'see' - by our retinal receptors detecting said 'photons'.
          • If mere observation ruins it, what the hell do you think shooting particles at the stuff is going to do?
            • it is not that the particles are ruining it, it is that quantom probability states that when you do not observe an object you can not make an asumption on its state. hitting it with particles will do nothing since we realy don't know if the particles are hitting it or not. what we are observing is the quantom entangles photons that have never been in the box and that is what give us the immage.....quantom entangle ment is the instant communication of 2 sub atomic particles. (this is what puts the GR folks on there head since 2 quantom entangeled particles could be 1,000,000 Lightyears away from each other, but they can communicate to each other instantly which would make that communication faster than light which is impossable according to GR.
              • If I shoot a bullet through the center of 3 pieces of paper all one inch a part at signifigant speed, I KNOW it will hit the forth one that I can't see if it's an inch away. Physics. And you can damned well bet that it changed things. (Note: I do believe in the theory of quantum *).

      • Damnit! (Score:5, Informative)

        by nanojath ( 265940 ) on Wednesday December 05, 2001 @05:28PM (#2661686) Homepage Journal
        Yeah yeah, it's all funny but it ticks me off that nobody is pointing out that The principle illustrated in Schroedingers "cat" thought experiment are NOT THE SAME as the Heisenberg Uncertainty Principle. In fact, it ticks me off that nobody knows what the Uncertainty Principle is really about and people constantly confuse it with the whole indeterminate quantum particle state and whether does in fact create quantum indeterminacy on the macro scale (if a tree falls in the forest...) issue. Heisenberg's Uncertainty Principle establishes a mathematically defined absolute uncertainty balanced between the momentum and position of a quantum scale particle. The corresponding thought experiment would be the gamma ray microscope [aip.org].
        • better type some random text in here to dodge the lameness filter -
          disclaimer: this post really was not intended as a troll or a flame - but if you're going to criticise people for not understanding Heisenberg's Uncertainty Principle, maybe you should help those who don't to do so.

          • Basically, a quantum particle - like an electron - exists in a somewhat undefined state. Its location and energy are not fixed, but exist more as a set of probabilities. These probabilitiy fields are calculable and are the basis for electron shell level/sublevel 3d models.

            The thing that makes all this interesting is that the certainty that a particle's position and energy level can be determined are limited. The more you define one, the fuzzier the other gets. This is not an observational thing, but an intrinsic property, as has been demonstrated by cooling some Cs atoms to

            What Schroedinger's cat is all about is the fact that quantum state (the probability cloud) does not collapse until observed. I suppose that means interaction, though Physicists keep calling observation. The cat is representative of some quantum particle in an indeterminate state. It wanders between quantum energy levels until you observe it. Then the quantum state collapses into one of these levels and interacts. This also has been confirmed (the weird travel in between adjacent energy levels) - Some scientists found that they were able to keep a group of atoms from changing energy levels by constantly observing them, whereas another group, which was observed less frequently, did change levels.

      • Re:Schroedinger's Cat (Score:4, Informative)

        by yesthatguy ( 69509 ) on Wednesday December 05, 2001 @05:30PM (#2661691) Homepage
        *Anything* which firmly establishes the state of the cat will collapse the wave function. If you burn the box in a crematorium, the cat is definitely dead -- no uncertainty. If you "see" into the box using a method other than opening it, then you know the result. There are many ways to collapse the metaphorical wave function, observing it is just the most direct way, and also relates most directly to the position of an electron, which can best be determined by observation, though not with the naked eye.
        • Actually, Schroedringer's cat, being a classsically sized critter, is saved from the being a member of the living dead by decoherence.

          How decoherence killed schroedringer's cat [nature.com]

          Maybe one day we'll be able to figure out how to keep cats in superimposed states, but for the time being Schroedringer's gonna have to decide whether to whack the cat before he closes the lid.

        • Re:Schroedinger's Cat (Score:3, Funny)

          by Anonymous Coward
          On a related note, I solved Schroedinger's cat a few years ago. What you do is perform the two-slit experiment [uoregon.edu], with single electrons, with a device to measure which slit the electron goes through.
          If you place it right, such that the CRT screen is outside the chamber, but the slit-measurement device displays its output only to the cat, then the wave of the electron breaks down iff:
          1. cats have souls (meaning they consistently break down quantum phenomena by observation, or something like that)
            AND
          2. the cat is alive

          If the cat is dead, the wave should not break down, so the interference pattern should show on the screen. If cats go into a quantum state of being half dead, the interference pattern would always show, otherwise 50% of the time the interference pattern would disappear.
          The actual solution is left to the reader.

          -- TDR

      • Re:Schroedinger's Cat (Score:5, Informative)

        by Faramir ( 61801 ) on Wednesday December 05, 2001 @05:31PM (#2661698) Homepage Journal

        This is a good question, and there have already been several good answers. However, I don't feel like they've really answered your question.

        Far from destroying the uncertainty principal, the article indicates that one of the "spooky" things about quantum holography is, essentially, the exploitation of the uncertainty principle.

        Now, as to direct observation and the uncertainty principle: perhaps these should be explained for the casual /.'ers out there.

        The uncertainty principle says that we cannot know exactly both the position and momentum at the same time. Momentum is a combination of mass and velocity. Mass often remains constant, so sometimes this is stated as "position and velocity" instead. Now, I used the word "exactly", and I meant just that. We can have a good idea of both numbers, but the more exact one measurement is, the less exact the other measurement will be. Basically, think of it this way: if we take a probe, like the tip of a pencil, and move it around till we find exactly were a particle is, we'll find it. But we'll also hit it and change its momentum.

        Now, all observations require some kind of probe, be it pencils, electrons, or photons (light). A related feature of quantum mechanics is that the equations we use to determine where a particle (or wave, they're the same thing at this level) is going (the famous Schrodinger equations) don't actually tell us where a particle is going--only where its likely to go. So we don't even know how to say where it is going to go. In fact, it is considered that a particle does not have just one specific path until the particle has been measured.

        In our case, that measurement--that is, the observation of the photons--occurs at the wall of the chamber. And from this data, convoluted equations work backwards to figure out what the photons bounced off of.

        Hope that helps...

        • The uncertainty principle has nothing to do with the nature of measurement, or probes. It is inherent in the quantum system. It is very sad to see this same confusion again and again.

          In quantum mechanics, the momentum distribution of a particle is the Fourier Transform of its position distribution. When the position distribution is narrower, the momentum distribution is wider, and vice versa. This is the basic property of FT. In fact there's a simple counter-argument to the probe effect, because when you hit something with a certain impulse and you know the mass of the particle, you can predict how the hit affects its motion.

          [Disclaimer: IAAP]

          • Re:Probes?! (Score:3, Informative)

            by statusbar ( 314703 )
            I like to explain it this way:

            Take a .wav file of a sine wave and edit it with your favourite sound editor. Zoom in so you see 100 cycles. Measure the time 100 cycles takes. From that you can calculate the frequency of your sine wave. At what time did this event occur? Well, the event is spread out over time. So we don't know the accuracy of the timing of the event very well.

            Now zoom in more so only 1/2 a waveform shows. Measure it. calculate the frequency. You now have more accuracy in the timing of the event, but less accuracy of the frequency.

            Heisenberg's principle is NOT the confusing thing about physics - it is plain reality! The thing that really is the source of the confusion is that the energy of a particle is related to its frequency - Just like the time and frequency were related in my example.

            *IANAP*

            --jeff
        • so, you're saying that, because math is an imperfect tool for deriving the particle's exact location, that the particle is not in an exact location?

      • Meow (Score:3, Funny)

        by Kenshin ( 43036 )
        If the cat meows, would that break the uncertainty principle?

        • Re:Meow (Score:2, Interesting)

          by Faramir ( 61801 )

          No. At this point, there is no established physical way to "break" the uncertainty principle. I'm not sure why it is not the "uncertainty law" at this point--perhaps this is a subtlety of the way the principal was derived. Nevertheless, it has the tenacity of a law of nature, and will not "break". The equation will not be violated--the uncertainty (or change) in position squared times uncertainty (or change) in momentum squared will alwasy be greater than or equal to Plank's constant divided by 2 (dx^2 * dp^2 >= hbar)

      • This has nothing to do (as others pointed out) with the Uncertainty Principle.

        The Schroedinger's Cat thought-experiment is totally different.

        ANd how does this bother the Cat problem at all? It doesn't.. if you observe the Cat in the box, in any way whatsoever, you have now observed it, and hence, caused it to assume a known state.
    • Actually, I got bored last week and opened the box. The cat died of starvation and has been decomposing for years. The radioactive isotope still hasn't decayed, however.
    • It wasn't actually Shroedinger's cat. He was a dog person. He used his girlfriend's cat, which he didn't like too much anyway.
    • Given that this theory is what? 40-50 years old. I would guess that the cat is dead, regardless of the isotope.
    • http://www.sciam.com/explorations/061796exploratio ns.html

      http://users.ox.ac.uk/~jsw/Schroedinger.html
    • Nothing is observed directly. Sad, but true.
    • Schroedinger's gonna have to rephrase the question - is the cat dead or just sleeping?
    • You could always just smash the box with a sledgehammer, and leave it there. Then you'd never have to worry whether the cat is alive or not, and could worry about more important things :)

  • Psychic? (Score:1, Offtopic)

    by s20451 ( 410424 )

    Physicists succeed where psychics fail.

    Sure, but can it tell me whether my wife is cheating on me? Or that I will meet a mysterious stranger after a journey of great distance?

  • No luggage scanning here (Score:5, Insightful)

    by Rob Parkhill ( 1444 ) on Wednesday December 05, 2001 @04:50PM (#2661465) Homepage
    The article seems to imply that you need a specially constructed sphere to make this work. One that lets light in at a specific point, and allows no light out. It also is built in such a way to detect when a photon hits the inside surface. Just take a look at the diagram [aip.org].

    So unless someone is stupid enough to try and sneak a bomb onto a plane in one of these spheres, it's not much use to the security guards.
    • So unless someone is stupid enough to try and sneak a bomb onto a plane in one of these spheres, it's not much use to the security guards.

      We could always pass a law mandating that all bombs being carried on by terrorists be enclosed in this type of sphere.

      And if that didn't work, we could always require that the device be clearly labeled "BOMB". I think a $300 fine should be sufficient penalty for this, don't you? At least it would be if we were talking about corporate violators...

      • There is no need to label it "BOMB" if you just require all bombs use the classic bomb shape: bowling ball sized black spheres with a large fuse on top. A stick or bundle of TNT should be OK too, assuming it is bright red and also uses a lit fuse.
    • true, but a few years ago, reasearchers transported a photon from point a to point b with out the photon traversing the space in between. this would let you get the photons into the container with out having to have a hole......of cource reading the results is a diffrent issue.
    • Don't dismiss it too hastily!
      The specially constructed sphere is the easiest, and thus first, configuration to be tried in the lab.

      All they need to do is require all interior luggage surfaces be built from these time-reporting light sensors (and maybe prevent travellers from putting anything else in the bag if they have a bomb), and voila! No time-and-cost-prohibitive bomb-sniffing machinery!
    • So unless someone is stupid enough to try and sneak a bomb onto a plane in one of these spheres, it's not much use to the security guards

      Reminds me of the old joke...

      In the early days of Rocket Science(tm), they were trying to figure out how to protect the astronaut from acceleration. So they hired one of the leading physicists of the day to investigate.

      A month later, he came back with a solution. He got up in front of the NASA bigwigs, and said, "First, assume a perfectly spherical astronaut..."

  • Peering into luggage.. (Score:3, Funny)

    by billn ( 5184 ) on Wednesday December 05, 2001 @04:53PM (#2661481) Homepage Journal
    Would spare them from the dreaded Dirty Laundry DoS attack frequently perpetrated at Customs. =)
  • As I see it, if you CAN'T see the back side of an object, then you can't see it!

    You can assume what it looks like and then create an image out of that assumption, but unless you are looking directly at it, you'll never know.

    • As I see it, if you CAN'T see the back side of an object, then you can't see it! You can assume what it looks like and then create an image out of that assumption, but unless you are looking directly at it, you'll never know.

      Ah, but what if I knew what it looked like before setting the whole thing up? If my hologram looked like the original, as I saw it in the first place, then is this not accurate?

      I suppose you could argue collapsing wave functions and quantum probability, but I'd think that was pushing it, no?

  • More important implmentations (Score:4, Insightful)

    by scott1853 ( 194884 ) on Wednesday December 05, 2001 @04:55PM (#2661493)
    Why does everybody still have airport security on their brain still? Think if this can be used in medicine.

    No more exploratory surgery. Quickly detect cancer growths.

  • X - Ray Specs (Score:4, Funny)

    by __4096 ( 526163 ) on Wednesday December 05, 2001 @04:55PM (#2661496)
    Perhaps somone will be able to make a pair of X-RAY specs that actually work! :)
  • I called the phone number listed in the article. Now the website and his phone have been /.ed! That really sucks.

    • According to the scheme, the inside of chamber would be designed
      to detect the time when a photon hits the wall but not where it hits.
    hey! this wont't work with any random luggage...
    this only works with special luggage that can detect when a photon hits its inner lining...
  • The photons merely bounce off the surface of the object and hit the detector wall. The reconstructed image is therefore only the surface contours of the object and not the contents, if any. Would likely have to use a different matter beam to peer inside baggage.

  • Dunno if their idea works... (Score:5, Funny)

    by jd ( 1658 ) <imipak@yahoGINSBERGo.com minus poet> on Wednesday December 05, 2001 @04:57PM (#2661518) Homepage Journal
    ...but I get to check two boxes in Slashdot Buzzword Bingo. Just a few more to go....
  • For the moment, quantum holography exists only on paper. But the researchers assert that there are no technological obstacles to the proposal, and they hope to begin building an experimental system soon.

    Correct me if I'm wrong here, but according to the article this process relies on quantum entanglement. As far as I know this has never been achieved on a large scale - only in single pairs.

    As I see it here this would require two lasers to be emitting entangled beams. I've never heard of a way this can be done. Without, as far as I can see, this process would not work. Seems to be a rather large sticking point... though I don't know how many photon pairs they actually need out of those beams. Anyone know more about this?

    None the less, the theory is 'spooky' indeed.

    • Correct me if I'm wrong here, but according to the article this process relies on quantum entanglement. As far as I know this has never been achieved on a large scale - only in single pairs.

      IANAPhysicist, but...
      Doesn't the uncertainty principle and the whole probability function idea of quantum mechanics suggest than a single photon pair would be all you'd need for the whole object? Theoretically, you could superimpose the probabilities of it bouncing off every single surface of the object at once to get the whole thing. The article mentioned that they would measure when the particle hit the sphere, not where, so that measurement wouldn't disrupt anything.

      Now how do they extract and superimpose all those probablilities.

  • Airports? (Score:1, Offtopic)

    by Legion303 ( 97901 )
    Screw the airports. Send one of these to the admin of www.xxxgirlsongirls.com stat!

    -Legion

  • It seems like this type of device would be more useful when you know what's in the sealed container and want a holographic image of it. So maybe you have an Xbox controller and you want to send someone a holographic image so they can see how huge it is. But since you need one of these special compartments, I don't think it will be very useful for seeing things inside any old container, such as checked luggage. Unless I misunderstood how this thing works?
  • . . .
    propose to create holographic images of objects concealed in a spherical chamber. Ideally, a small opening in the chamber wall permits light to enter, but lets no light out. The photons in a beam of light directed through the hole scatter from the enclosed object, and ultimately strike the inner wall of the chamber (see figure).

    So it's not sealed, but a small opening. I dunno if I want people making holes in my luggage.

  • What's That?! (Score:3, Funny)

    by Renraku ( 518261 ) on Wednesday December 05, 2001 @05:03PM (#2661553) Homepage
    "Look! I think its a bomb!"
    "Sure does look like one..seize her!"
    Five minutes later.
    "There was no bomb in here..WTF?"
    "It would have been in there if we hadn't looked!"

  • In Airports? I think not... (Score:3, Funny)

    by cscx ( 541332 ) on Wednesday December 05, 2001 @05:08PM (#2661573) Homepage
    Could it lead to quantum luggage scanners at the airport?

    I don't believe so. I personally feel the problem with airport security is not the type of equipment used, but the incompetence of some of the security people employed there. You've heard the security breach stories on the news.

    "What is that, a hairdryer with a scope on it ?... That looks okay, keep it moving". "Some sort of bowling ball candle ? That's fine, just... we don't want to hold up the line, don't hold up the line"
    Jerry Seinfeld on Airport Security

  • In a few years, they wont even need to open your suitcase, just put on VR helmets with the passenger and ask them to explain every piece of luggage as it rolls by on a VR conveyor belt, after being unpacked with detectors and fast graphics cards.

    Sure makes repacking a breeze!

  • Faster than light communication (Score:4, Interesting)

    by pete-classic ( 75983 ) <hutnick@gmail.com> on Wednesday December 05, 2001 @05:16PM (#2661612) Homepage Journal
    I don't really understand quantum entanglement but . . .

    Couldn't you use it to communicate instantly over any amount of distance?

    Imagine:

    You are at point A (say, earth) and I'm at point C (say, a spacecraft) and we have a buoy, at point B, precisely half way between us. Let's say that you and I are one light-year apart, and that buoy has been splitting a beam of photons between the point where I am and the point were you are for the last six months.

    You have a photoreceptor oriented 90 degrees out from the beam, and I have a mirror at 45 degrees, hooked up to a solenoid. I type you a message in morse code on a switch that controls current to the solenoid. You see it in real-time.

    I'm sure that either 1. there is a really good reason why this won't work in theory or 2. someone else has proposed it.

    Can someone give me a reference either way?

    -Peter
    • I don't have a reference for you, but I can say that no, quantum entanglement does not allow FTL communication. To do anything interesting, you need to communicate information about the observation you made on one of the particles. Imagine twins -- one male, one female. They go to the two poles; at the North pole, somebody looks at one, and *boom*, she's female and the other one is male -- instantly. The people at the South pole look a microsecond later, and see that their twin is male. Okay... so? The people at the North pole haven't transmitted any information, even if the action occurred *instantly*.

      The article doesn't make it clear, but the measurement taken in the chamber must, I have to assume, be transmitted and used in constructing that second image (it doesn't just *happen*; you can't shine a beam of light, even entangled photons, and expect them to magically scatter off nothing. When the first entangled beam is measured, quantities of the second half are determined, but that doesn't make them scattered, since it was *possible* they were in that state already... it has to be possible, that's how quantum physics works). It sounds like the information would be used in a second beam interfering with the intangled beam, but I'm not certain from the article... but I can guarantee that information has to be used.
    • Comment removed based on user account deletion

    • Re:Faster than light communication (Score:5, Interesting)

      by Mr. Slippery ( 47854 ) <.tms. .at. .infamous.net.> on Wednesday December 05, 2001 @06:44PM (#2662197) Homepage
      Couldn't you use it to communicate instantly over any amount of distance?

      No, you couldn't. :-)

      Your mirror scenario wouldn't be making any measurements on the incoming photons, I don't see that it has anything to do with entanglement.

      Let's look at another example that gets closer to - but turns out not to be - instantaneous communication. It's been a while since I studied this, so real physicists please correct me, but I think I remember the gist of it.

      We'll use polarization as an example. Quick review: every photon is polarized at some angle. If it hits a detector that's at the same angle, it passes though; a detector at 90 degrees to its angle, it's blocked; and at some angle in between, it may or may not pass through, but if it does it will now have the new angle of the detector (i.e., a 45 degree photon hitting a 0 degree piece of polarized material has a 50% chance of being blocked at a 50% chance of passing with its polarization at 0 degrees).

      The polarization vector is a quantum superposition of the 0 degree and 90 degree states. If two photons are entangled, and one gets measures and "snaps to" one of these states, its entangled partner always "snaps to" the same state. (Or maybe it always snaps to the opposite state. I forget. Doesn't matter for this example.)

      Let's say that our entangled photon source is sending out beams that are polarized at 45 degrees (i.e., in a superposition of 0 and 90 degrees). The sender - call her Alice - sets her polarization detector to either 0 degrees (to transmit a "dot") or 90 degrees (to transmit a "dash"), and her photon randomly snaps to one of these polarizations. If it happens to snap to the matching one, it passes thru the polarization detector.

      A light-year away, the matching photon in the detector belonging to the receiver (call him Bob) spookily snaps to the same polarization direction. Bob's all set to make a measurement, but which way should be set his polarization detector? If he sets it at 45 degrees, then regardless of whether the photon is at 0 or 90 it has a 50/50 chance of passing through, so he'll see half the photons pass. If he sets it at 0, the incident photon has (from Bob's perspective, not knowing whether the next bit of the message is a "dot" or a "dash") a 50/50 chance of being polarized at 0 at 90 degrees, so he'll see half the photons pass. Same if he sets it at 90.

      Even though the photons were linked, and each instantaneously "knew" what was happening with the other one, no information can be recovered from the beam, because what the photons do is still random.

      (However, by changing this around a little bit Alice and Bob can generate an unbreakable cryptographic key - search Google for "quantum cryptography".)

      • I have practically no background in quantum physics, but:

        Couldn't you, say, devise a system where each "bit" of information was transmitted for a certain length of time? After all, this is basically a serial communication system, so as long as you know the time for a bit, you wouldn't have to know the polarization of every single photon passing through--you could just catch the 0-degree (or 90-degree, either way) photons, and assume that when you weren't getting photons then they were all polarized the other way, giving you a bit of the opposite value.

        Or so it seems to my simple mind, anyway... is there a reason this wouldn't work?

    • Yes and No (Score:2, Interesting)

      by ArcSecond ( 534786 )
      There is a really good book I read about stuff like this a few years ago, called "Schrodinger's Kittens". To sum it up, the guy says there is ANOTHER way to look at quantum weirdness, other than the "Standard/Copenhagen" model.

      The idea is that since photons travel at the speed of light (duh), they don't experience "time", and can actually make a "choice" about the path they are going to take, so that an entangled pair of photons "agree" as to where they will be in the future. This has the affect of looking to us like there is an "instantaneous transmission" of information from one to the other, which would violate causality from the standard view. The "choice" is the ability of the photon to "feel out" all the possible paths it could take, and select an event in the future to which to tie itself to. This might be interpreted as a basis for "fate", which is fine by me, since that's the way I lean anyhow.

      Obviously (as IANAP) this explanation is worded poorly and not really an accurate representation of the weird math involved. But, while information is "traveling back in time", I don't think there is a practical way to use this effect as a communications medium. Maybe you could have four entangled beams (two each for two observers)?

    • No.

      This concept was originally conceived sometime around 1930 by einstein, podolsky, and rosen as an argument intended to torpedo quantum mechanics.

      basically they pointed out that quantum mechanics predicts that if you prepared a four state quantum mechanical system (ie 2 qubits) in a certain way (creating an EPR pair) they would exhibit "spooky action at a distance". at the time it was a fundamental principle that cause and effect had to obey the speed of light and therefore quantum mechanics was broken.

      turns out there is massive amounts of evidance that cause and effect can be instantaneous over any distance and quantum mechanics goes on to be the most succesful scientific theory in history.

      the scenario is this: alice and bob create an EPR pair, and then each takes one to opposite ends of the universe. when alice measures the state of her qubit, bob's qubit instantly becomes a known quantity.

      it has been proven that to use this effect for communication requires the communication of classical bits of information (i believe it is the result of alice's measurement) which are governed by the speed of light. hence quantum entanglement can not be used as a truly instant messaging transport.

      however, you can use this effect to achieve perfectly secure cryptographic key distribution and this has actually been done several times.

      quantum computing is super cool and might actually be practical. check out http://www.qubit.org for some well chosen tutorial papers and links.
  • You can get an idea of what something is shaped like in more conventional ways. Like X-ray.

    What is really impressive is that they can see what the surface of a flat object, like a photograph, looks like. Neat!

    -Peter
  • First, I'd like to point out that quantum computation and quantum encryption are two almost completely separate concepts. Quantum encryption is based on the fact that quantum states cannot be measured without altering. The most common example is the polarization of a photon, but it will work for any quantum state, so long as there exist, effectively, two unique states that can transmit the data.

    Quantum computation, however, is much more complex and much more interesting. Quantum computers are based on the concept of quantum entanglement, the ability of a quantum state to exist in a superposition of all of its mutually exclusive states: It's a 1 and a 0. However, this is not as easy to use as one might think. While it's true that if you have n quantum logic gates you have the ability to input 2^n data values simultaneously (as opposed to only 1 piece of data if you have n digital logic gates), this is not going to be the end of classical computing for a few reasons. First, quantum computers have to be perfectly reversible. That means for every output there's an input and vice versa. And there has to be no way of knowing the initial states of the data. You don't process data, you process probabilities in a quantum computer; if you know exactly what any one value is throughout the computation, you can find out all of the values: the superposition ends and you're stuck with a useless chunk of machinery. This means YOU CAN ONLY GET ONE RESULT FROM ANY QUANTUM COMPUTATION, THE END RESULT. You can't see what the data in the middle is or the computer becomes useless. (Landauer's principle makes heat loss data loss. When your processor gets hot, it's losing data. If the same thing happened to a quantum computer, it wouldn't be quantum anymore.) Decoherence is what happens when you randomly lose data to the environment by design, not by choice, and the superposition ends. This is bad for Q.C. Oh, and quantum computers can only do *some* things faster, like prime factorization and discrete logarithms. Not multiplication or addition. Plus, the circuits that would do basic arithmetic would be bigger and slower than what you've currently got.

    So what does this all mean? It means that quantum computers are going to provide some advantages (real quick big number factorization), and some disadvantages (that whole RSA standard). The most realistic initial use of quantum computers will be as add-ons to existing super-computers to resolve certain types of NP-Complete headaches that regular math can't simplify yet. At best they will someday be an add-on to your PC; but they will never replace the digital computer.~

    If you want more info, check out ahttp://www.qubit.org, it's got some decent tutorials.

  • ...a new, more efficient porn acquiring method for geeks - because most clothes are not entirely opaque and some light gets to the skin, can this be used to acquire 3D nude holograms of fascinating females that pass by?

  • Wow, all the ideas going through my head are just amazing me. Thieves could use this to see if someone's in a house, and slashdotters could use it to broadcast live porn!

  • Link to the real thing. (Score:4, Informative)

    by HughsOnFirst ( 174255 ) on Wednesday December 05, 2001 @05:28PM (#2661683)
    Here is a link to the [bu.edu]
    actual paper itself. It's a PDF file though

  • Hologram of a suitcase :-/ (Score:3, Funny)

    by karot ( 26201 ) on Wednesday December 05, 2001 @05:30PM (#2661694)
    OK, So we put a suitcase into one of these things at an airport, et VIOLA!...

    ... a hologram of a suitcase! Methinks this one will need work before it replaces the good ol' Airport Xray machine.

    Of course quantum entanglement is also how "they" propose to achieve the matter-transporter, so forget looking inside the luggage, we can just send it on ahead :-)
  • The given example apparatus would not be a practical device in any way. It needs a way to allow photons in, and could just as easily allow photons out; additionally, the inner surface of the sphere needs to be a photon detector with very precise timing. It doesn't see anything a camera inside the sphere couldn't see.

    This is about exploring quantum entanglement. When lasers were invented, nobody knew what to do with them. Everybody thought "Death ray!" which was pretty silly in retrospect; that's a minor application. Then, bit by bit, they found thousands of ways to apply them that revolutionized all sorts of practical devices and allowed entirely new ones.

    Developing this would be breaking old rules about what is and isn't possible, and though it's hard to guess exactly what it's good for, you can bet it'll be good for some amazing new technologies.

  • background information about holography (Score:4, Informative)

    by tcc ( 140386 ) on Wednesday December 05, 2001 @05:40PM (#2661750) Homepage Journal
    For those of you interrested in holography:

    Holography basics (aimed at Highschool students level). [cmaisonneuve.qc.ca]

    Books and information on Holography [rossbooks.com]

    Some more holography Theory> [hologram.net]

  • Take a closer look (Score:3, Insightful)

    by meatpopcicle ( 460770 ) on Wednesday December 05, 2001 @05:58PM (#2661913) Homepage
    IT JUST CREATES A 3D IMAGE OF A 3D IMAGE!
    -theres no X-Ray vision here! For luggage they would be able to say "I think its a suitcase"
    -it does seem "spooky" though
    -it does have potential uses that could be really cool. Remote surgery, biometrics, 3D video

  • Photosensitive Sphincter: anyone read the article? (Score:3, Funny)

    by NickFusion ( 456530 ) on Wednesday December 05, 2001 @06:52PM (#2662260) Homepage
    Good lhord, did anyone actual read the damn article? Here's a clue: No.

    The technology described will not scan your luggage, nor will it make body cavity searches obsolete, unless you have a spherical, photosensitive rectum.

    Not a cure for cancer, or a replacement for a cat scan or MRI.

    What the technology excels at is showing you what's inside a specially constructed sphere. This information could also be garnered with a sufficiently large hammer.

    A cool physics party trick, and some interesting basic research. That's about it.

  • Not entirely new... (Score:3, Interesting)

    by Pig Hogger ( 10379 ) <pig.hogger@g[ ]l.com ['mai' in gap]> on Wednesday December 05, 2001 @08:59PM (#2662870) Journal
    It is possible now to view hidden objects by ultrasonic holography... I believe that this process has even been (gasp!) patented more than 25 years ago...

    The object has to be at the bottom of a pool filled with some opaque liquid; a transducer is immersed, bathing the object with ultrasound. Sound waves reflect on the object, and they form an interference pattern on the surface, which is lit by coherent light, thus forming a virtual image of the object.

    One caveat, though... Given the ***BIG*** difference of wavelength, the virtual image appears to be quite far, and has to be viewed with a telescope...

  • And at FAR below the price (even the alleged 'Hologram' arcade game from Sega in 1991 or so was based on the same principle):

    http://www.exploratoriumstore.com/miragemaker.ht ml

  • Original article (Score:4, Informative)

    by Vadim Makarov ( 529622 ) <makarov@vad1.com> on Wednesday December 05, 2001 @10:22PM (#2663157) Homepage
    I'm surprised nobody put a link to the original article.

    Abouraddy,A., Saleh,B., Sergienko,A., and Teich,M. Quantum holography [opticsexpress.org] (PDF, 169KB, 8pages), Optics Express, 9, 498-505 (2001).

    Read the damn thing (if you can :-)), then discuss.

  • IANAP but two of these and an entangled atomic laser = mass duplication / transportation device?

    With an atomic laser it is theorized that you can create a matter hologram, whatever that is, supposedly just like the original.

    Wonder if it hangs around after you turn off the reference beam? It would be a bitch if you lost the original.. poof!
  • It's baffling to me that no one seems to have pointed this out, but the important applications of this technology are likely to be in light microscopy, not scanning luggage. Particularly light microscopy of biological tissues. This could be a very important advance.

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