Quantum Holography

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?"

Comments

Schroedinger's Cat

[gblues]

Great! Now we'll be able to tell Schroedinger once and for all whether his stupid cat is dead or not.

Nathan

Re:Schroedinger's Cat

[the_2nd_coming]

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?

Re:Schroedinger's Cat

[Octal]

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.

Re:Schroedinger's Cat

[big_groo]

Uh...that's how we 'see' - by our retinal receptors detecting said 'photons'.

Re:Schroedinger's Cat

[autocracy]

If mere observation ruins it, what the hell do you think shooting particles at the stuff is going to do?

Re:Schroedinger's Cat

[yesthatguy]

*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.

Re:Schroedinger's Cat

[Faramir]

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...

Re:Schroedinger's Cat

[autocracy]

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 *).

Re:Schroedinger's Cat

[jabber01]

He's not dead.. He's pining for the fjords!!

Re:Schroedinger's Cat

[Happy Monkey]

great ... in a orwellian twist, a quantum device is created that invalidates the principles of quantum physics upon which it is based - to be followed shortly thereafter by its use in airport security.

Re:Schroedinger's Cat

[Anonymous Coward]

On a related note, I solved Schroedinger's cat a few years ago. What you do is perform the two-slit experiment, 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

[jafac]

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?

No luggage scanning here

[Rob Parkhill]

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.

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.

Re:No luggage scanning here

[frank_adrian314159]

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...

Peering into luggage..

[billn]

Would spare them from the dreaded Dirty Laundry DoS attack frequently perpetrated at Customs. =)

More important implmentations

[scott1853]

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.

Re:More important implmentations

[Syberghost]

No more exploratory surgery. Quickly detect cancer growths.

Yeah, I can see it now:

"After putting you in this big sphere and exposing you to massive amounts of electromagnetic radiation, we've determined that you do indeed have skin cancer."

X - Ray Specs

[__4096]

Perhaps somone will be able to make a pair of X-RAY specs that actually work! :)

Dunno if their idea works...

[jd]

...but I get to check two boxes in Slashdot Buzzword Bingo. Just a few more to go....

Some info for those that don't know...

[Mustang Matt]

http://www.sciam.com/explorations/061796exploratio ns.html

http://users.ox.ac.uk/~jsw/Schroedinger.html

What's That?!

[Renraku]

"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...

[cscx]

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

Faster than light communication

[pete-classic]

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

Re:Faster than light communication

[SeanCier]

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.

Re:Faster than light communication

[Mr. Slippery]

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".)

Re:Faster than light communication

[Mr. Slippery]

If you change an entangled photon in any way, the other one instantly changes the same way.

It's more correct to say that if one entangled particle changes, the other changes too. But that only helps you do instantaneous communication if you can change an entangled particle in exactly the way you want. No one's figured out how to do that.

As far as we can tell at present, quantum nonlocality and "spooky action at a distace" exist, but cannot be made to transmit any information.

Looking at a paper I did about ten years ago, I found the following quote from Nick Herbert's Faster Than Light that summarizes the situation:

Eberhard's proof applies to the quantum patterns...[it] guarantees that large-scale quantum patterns will never be observed to be connected faster than light. Bell's theorem, on the other hand, applies to the individual quantum events themselves, and proves that these little quantum jumps must be connected faster than light...Bell's theorem can coexist with Eberhard's proof because they each refer to different aspects of a quantum measurement. Bell's theorem...can also exist with the COP rule forbidding all superluminal connections that can be used for signaling, because these Bell-mandated FTL jumps occur in an utterly random manner.

Link to the real thing.

[HughsOnFirst]

Here is a link to the
actual paper itself. It's a PDF file though

Damnit!

[nanojath]

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.

Hologram of a suitcase :-/

[karot]

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 :-)

Re:Hologram of a suitcase :-/

[Jburkholder]

>et VIOLA!...

Ah yes, the most-often overlooked of stringed instruments! Mind you, I like a nice cello, myself.

background information about holography

[tcc]

For those of you interrested in holography:

Holography basics (aimed at Highschool students level).

Books and information on Holography

Some more holography Theory>

Meow

[Kenshin]

If the cat meows, would that break the uncertainty principle?

Re:This is crazy

[MacDuff]

Knowing the particles are entangled is extra information. If I know bits A and B are either both 0, or both 1 (fully entangled), and I observe bit A to be 0, I know B is 0. No information or state is transferred between the two particles after the initial entanglement.

This can still be performed if, for example, bits A and B are on different HDs, and I ship one across the country. Suddenly, by reading one, I can tell someone across the country what they will read at the address where their bit is on the disk.

Take a closer look

[meatpopcicle]

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?

[NickFusion]

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...

[Pig Hogger]

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...

Original article

[Vadim Makarov]

I'm surprised nobody put a link to the original article.

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

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

Re:Probes?!

[statusbar]

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